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Compiled by Mrs. G. Campbell
Copyright @ 2010
COURSE OUTLINE .............................................................................................................. 7 LECTURE 1 – INTRODUCTION (1/2 HOUR) .................................................................. 14 DEFINE OPERATING SYSTEM.................................................................................................. 14 TYPES/CATEGORIES OF OPERATING SYSTEMS ....................................................................... 15 Stand-alone ...................................................................................................................... 15 Network ............................................................................................................................ 15 Embedded ........................................................................................................................ 16 TUTORIAL QUESTIONS .......................................................................................................... 16 PRACTICE MCQS ................................................................................................................. 16 THE HISTORY AND DEVELOPMENT OF THE OPERATING SYSTEM ............................................... 18 TUTORIAL QUESTIONS .......................................................................................................... 21 PRACTICE MCQS ................................................................................................................. 21 LECTURE 2 - OPERATING SYSTEMS FUNCTIONS (1 HOUR) .................................. 23 FUNCTIONS .......................................................................................................................... 23 WHAT IS A USER INTERFACE? ............................................................................................... 24 SERVICES ............................................................................................................................. 25 Buffering .......................................................................................................................... 25 Spooling (Simultaneous Peripheral Operation On-Line) .................................................. 25 Other Services .................................................................................................................. 26 TUTORIAL QUESTIONS .......................................................................................................... 27 PRACTICE MCQS ................................................................................................................. 27 LECTURE 3 - SOFTWARE AND FIRMWARE (1/2 HOUR) ........................................... 29 SYSTEM SOFTWARE.............................................................................................................. 29 APPLICATION SOFTWARE ...................................................................................................... 29 FIRMWARE ........................................................................................................................... 31 TUTORIAL QUESTIONS .......................................................................................................... 31 PRACTICE MCQS ................................................................................................................. 32 LECTURE 4 - FILE CONCEPTS (1 HOUR) ..................................................................... 34 FILE ATTRIBUTES ................................................................................................................. 34 FILE OPERATIONS ................................................................................................................. 35 What the Operating System must do for each of the 5 basic file operations ...................... 35 TUTORIAL QUESTIONS .......................................................................................................... 36 PRACTICE MCQS ................................................................................................................. 36 LECTURE 5 - DIRECTORY SYSTEMS (2 HOURS)........................................................ 38 DIRECTORY OPERATIONS ..................................................................................................... 38 DIRECTORY SYSTEMS TYPES OF DIRECTORIES/DIRECTORY STRUCTURES ................................ 38 TUTORIAL QUESTIONS .......................................................................................................... 41
Operating System Concepts Mrs. G. Campbell Copyright @ 2010 Updated Jan 2010
PRACTICE MCQS ................................................................................................................. 41 LECTURE 6 - MULTI-PROGRAMMING AND TIMESHARING (1 HOUR) ................ 42 MULTI-PROGRAMMING ......................................................................................................... 42 TUTORIAL QUESTIONS .......................................................................................................... 43 PRACTICE MCQS ................................................................................................................. 43 TIME SHARING ..................................................................................................................... 44 TUTORIAL QUESTIONS .......................................................................................................... 44 LECTURE 7 - SCHEDULING CONCEPTS, CRITERIA, ALGORITHMS (6 HOURS) 45 SCHEDULING CONCEPTS ....................................................................................................... 45 TUTORIAL QUESTIONS .......................................................................................................... 46 PRACTICE MCQS ................................................................................................................. 46 SCHEDULING CRITERIA ......................................................................................................... 48 TUTORIAL QUESTIONS .......................................................................................................... 48 PRACTICE MCQS ................................................................................................................. 48 SCHEDULING ALGORITHMS ................................................................................................... 49 First Come First Served or First In First Out (FCFS/FIFO) ............................................. 49 Shortest Job First (SJF).................................................................................................... 49 Priority ............................................................................................................................ 50 Round robin (RR) ............................................................................................................. 50 Pre-emptive ...................................................................................................................... 50 Multilevel queues ............................................................................................................. 51 TUTORIAL QUESTIONS .......................................................................................................... 51 PRACTICE MCQS ................................................................................................................. 52 LECTURE 8- MULTIPLE PROCESSOR SCHEDULING (2 HOURS) ........................... 54 ASYMMETRIC MULTIPROCESSING .......................................................................................... 54 SYMMETRIC MULTIPROCESSING ........................................................................................... 54 HOMOGENOUS AND HETEROGENOUS SYSTEMS ...................................................................... 55 TUTORIAL QUESTIONS .......................................................................................................... 55 PRACTICE MCQS ................................................................................................................. 55 LECTURE 9 - MEMORY MANAGEMENT (1 HOUR).................................................... 57 INTRODUCTION .................................................................................................................... 57 TUTORIAL QUESTIONS .......................................................................................................... 57 PRACTICE MCQS ................................................................................................................. 58 MEMORY HIERARCHY........................................................................................................... 59 TUTORIAL QUESTIONS .......................................................................................................... 59 PRACTICE MCQS ................................................................................................................. 60 LECTURE 10 - BASIC MEMORY HARDWARE – BASE REGISTER, LIMIT REGISTER (1 HOUR) ......................................................................................................... 61 WHAT IS A REGISTER?........................................................................................................... 61 TYPES OF REGISTERS ............................................................................................................ 61 TUTORIAL QUESTIONS .......................................................................................................... 62 LECTURE 11 - LOGICAL VS. PHYSICAL ADDRESS SPACE (1 HOUR) .................... 63
Operating System Concepts Mrs. G. Campbell Copyright @ 2010 Updated Jan 2010
........................................... 80 LEAST RECENTLY USED (LRU) ........................ 69 MEMORY ALLOCATION STRATEGIES – FIRST FIT.................................................... 76 PRACTICE MCQS .......................................... 65 LECTURE 13 .................................................................................................... 67 TUTORIAL QUESTIONS ..................................................... 81 LECTURE 18 .................................................. 78 ADVANTAGES: ................................... 80 OPTIMAL REPLACEMENT .......................................................... 74 PRACTICE MCQS ......................................................... WORST-FIT ........................................................................................................... 68 PRACTICE MCQS ............................................................................................................................................................................................................................................................................... 67 CONTIGUOUS ALLOCATION ....................................... 80 LEAST FREQUENTLY USED (LFU) .............................................................................................................................. 80 ALLOCATION ALGORITHMS ..... 75 LECTURE 15 ..................................................................................... 82 DISADVANTAGES ............................................................ 70 LECTURE 14 – PARTITIONS AND FRAGMENTATION (1 HOUR)................................................................................................................................................................................................................................................................................................... 76 TUTORIAL QUESTIONS ....................... 64 LECTURE 12 – SWAPPING (1 HOUR) ............................................................................................................................................. Campbell Copyright @ 2010 Updated Jan 2010 3 ..................... 67 NON-CONTIGUOUS ALLOCATION ........................................................TUTORIAL QUESTIONS ................................................................................. 81 PRACTICE MCQS ..... 75 PRACTICE MCQS ............................... 70 PRACTICE MCQS ..............CONTIGUOUS VS NON CONTIGUOUS MEMORY ALLOCATION (4 HOURS) ............................................................................................................................ 79 DISADVANTAGES: . 76 VIRTUAL ADDRESS SPACE ........... G.. 82 ADVANTAGES ...............................................................................................................................................................INTRODUCTION TO VIRTUAL MEMORY (1 HOUR) ............................................ 79 LECTURE 17 .......................................................................................................... 76 LECTURE 16 ........................................................ 63 PRACTICE MCQS .......................................................................... 75 TUTORIAL QUESTIONS .................................................. 70 TUTORIAL QUESTIONS .......................................................................................................................DEMAND PAGING (2 HOURS) .............................. 80 MOST FREQUENTLY USED (MFU)........................................................................................................................................................................... BEST-FIT.......................................................................................................................................... 65 PRACTICE MCQS .................................................................................................................................................................................................. EXTERNAL................................................. 72 TUTORIAL QUESTIONS ... 80 TUTORIAL QUESTIONS .....................................PURE PAGING (2 HOURS) ............................................. 72 PARTITIONS......................................................................................................................................................... 82 Operating System Concepts Mrs.............................................................................................................................................................................. 74 FRAGMENTATION – INTERNAL........ 79 TUTORIAL QUESTIONS ...................... 65 TUTORIAL QUESTIONS ..................................................................................................................................................................... 80 FIFO ...................................................................................PAGE REPLACEMENT (3 HOURS) ...............
............................................................................................................................................... 100 LECTURE 24 .................................................................................................................................................................................................................................................................................................................................................................... 90 LECTURE 21 .................................................................. 92 DISK SCHEDULING ....... 91 PRACTICE MCQS ....... 91 OPERATIONS ON MOVING-HEAD DISK STORAGE ............................................................................ 88 RAM AND OPTICAL DISKS ................ 87 LECTURE 20 .................................................................................... 92 PRACTICE MCQS .......................................FILE SERVER SYSTEMS (1 HOUR) .......... 99 BACKUP TIPS ............................................................................................................................................. G............................ 100 PRACTICE MCQS ................................. 103 PRACTICE MCQS ..................................................................... 85 TUTORIAL QUESTIONS .................................MOVING-HEAD DISK STORAGE (2 HOURS) ................................................................................................... 83 LECTURE 19 – SEGMENTATION (1 HOUR) ....................................................................... 88 BLOCKS ................................................................................................................................. 93 First come first served (FCFS) ................................................... 101 LECTURE 25 ............................................................................................................ 83 TUTORIAL QUESTIONS ............. 93 TUTORIAL QUESTIONS ........................................................................................................................................................ 94 PRACTICE MCQS ............................................................................. 94 LECTURE 22 – RAID (2 HOURS) ............ 88 TUTORIAL QUESTIONS ....................................................................................................................................... 102 TUTORIAL QUESTIONS ......................... 99 GRAND FATHER.............................................................................................................................. 89 TUTORIAL QUESTIONS ....................... 89 DISK CACHING ............................................................................................................. 98 LECTURE 23 – BACKUP AND RECOVERY METHODS (1 HOUR) ............................................. FATHER...................................DISTRIBUTED FILE SYSTEMS (1 HOUR) ............................................................................................................................................................................................................................... 93 Shortest seek time first (SSTF) ................... 92 TUTORIAL QUESTIONS ............... 83 PRACTICE MCQS .......................................................AUXILIARY STORAGE MANAGEMENT (1 HOUR) ........................................................................ 95 RAID LEVELS ................................................... Campbell Copyright @ 2010 Updated Jan 2010 4 ......................... 95 TUTORIAL QUESTIONS ................................................................................................................................... 99 TUTORIAL QUESTIONS ......................................................................................................... 103 Operating System Concepts Mrs...................................................................................................................................................... 88 INTRODUCTION ........................................................................................................................................ 93 SCAN and C-SCAN ...THRASHING................................................................. SON TECHNIQUE FOR MAGNETIC TAPE ....................................... 101 TUTORIAL QUESTIONS ...................................................................................................................................................................................................................................... 93 LOOK and C-LOOK ......................................... 88 TUTORIAL QUESTIONS ....................................... 86 PRACTICE MCQS ... 91 MEASURES OF MAGNETIC DISK PERFORMANCE ......................................................................................................................................................... 88 TUTORIAL QUESTIONS ............................
..................................................................................................................................................... 104 MATH CO-PROCESSORS ........... 116 Denial-of-service............................ 108 Examples of RISC Processors. 109 CISC .LECTURE 26 .................................. 112 SUMMARY/CONCLUSION ........................................................ 104 TUTORIAL QUESTIONS .................................................................................................................................................................... FIREWALL ..................................................................................... 117 Virus protection...................... 106 Advantages of RISC .......................................................... 117 Encryption ................................... 104 PRACTICE MCQS ........................................... 115 PURPOSE OF SECURITY ............................................................................................................................................. 115 DEFINITION OF SECURITY.............. 115 FORMS OF SECURITY VIOLATION .................................................................................................................................. 120 Novell Netware .......... 116 Virus ................................CO-PROCESSORS (1/4 HOUR)................. 113 PRACTICE MCQS ................................................................................................................................................... Campbell Copyright @ 2010 Updated Jan 2010 5 ........................................................................................... 119 OS/400 ......................... 116 Trojan Horse ....................... 113 TUTORIAL QUESTIONS ..................................... G......... ENCRYPTION.....................RISC/CISC (3/4 HOUR) ............................................................................................................................... 116 Logic bomb .................................. 121 Operating System Concepts Mrs....................................................................... VIRUS PROTECTION.............................. 119 MS-DOS...... 105 LECTURE 27 .......................................................... 117 Authentication ................................................. 106 RISC (REDUCED INSTRUCTION SET COMPUTING) .................................................................................................................... 111 Disadvantages of CISC ...... 119 OS/2 ................................ 110 Advantages of CISC .......................................................................................................................................................................................................................... 104 DISADVANTAGES ......... 116 Worm ........................ 104 ADVANTAGES ................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................. 115 SECURITY THREATS AND ATTACKS ........... 113 LECTURE 28 – SECURITY (1 HOUR) .................................. 111 Examples of CISC Processors/Chips ................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... 119 UNIX............................................................................................................................................................................................. 117 AUTHENTICATION.......................................................... 117 PRACTICE MCQS ..................................................................................................................... 117 TUTORIAL QUESTIONS .............................................. 120 MacOS ................................................................................................................... 120 Microsoft Windows ....................................................................................................................................... 107 Disadvantages of RISC................................................................................................................................................................ 117 Firewall........................................................................................................................................................................................................................................................................................................................................ 112 CRISC.............................................................................................................................................. 118 CASE STUDIES .............................................
................................. G.............................. Campbell Copyright @ 2010 Updated Jan 2010 6 . 122 Operating System Concepts Mrs.................................. 121 REFERENCES ...................................................TUTORIAL QUESTIONS .........................................................................
virtual memory. process scheduling. program loading and linking system calls and system programs. understand the fundamental concepts of modern operating systems 2. appreciate the wide variety of operating systems within diverse platforms 3. 5. 3. 4. G. 2.COURSE OUTLINE THE COUNCIL OF COMMUNITY COLLEGES OF JAMAICA COURSE NAME: COURSE CODE: CREDITS: CONTACT HOURS: PRE-REQUISITE(S): CO-REQUISITE(S): SEMESTER: COURSE DESCRIPTION: This course presents the basic concepts of operating systems. GENERAL OBJECTIVES: Upon successful completion of this course. device and memory management. students should: 1. manipulate operating systems 4. Campbell Copyright @ 2010 7 . use system tools to execute various computer functions UNIT I .Introduction Specific Objectives: Upon successful completion of this unit. students should be able to: 1. deadlock and the tradeoffs in the design of large-scale multitasking operating systems. interrupt handling. define operating system describe the historical development of operating systems describe at least six (6) functions and services of an operating system explain the difference between application and system software define firmware Updated Jan 2010 Operating Systems Concepts CSYS2402 3 45 (45 hours theory) None None (2 hours) Operating System Concepts Mrs. Topics that will be examined include processes and interprocess communication/synchronization.
e. System Startup. 2. 2. Software and Firmware: a. d. h. c. b. Program execution. Two-level. b. G. f. Directory Systems – Single-level. Define operating system. Resource Allocation. I/O – (Buffering. list and describe at least five (5) file attributes describe at least five (5) file operations list at least five (5) directory operations describe at least four (4) directory structures compare and contrast the directory structures Content: 1. 4. Storage. students should be able to: a. File Concepts – File Attributes. Introduction: a. Error Detection 3. System Software b. Protection and Security. Acyclic-Graph UNIT III – CPU Scheduling Specific Objectives: (9 hours) Upon successful completion of this unit. File-system manipulation. User Interface. 5. The history and development of the operating system. 3. Campbell Copyright @ 2010 8 . Utilities UNIT II – Directory Systems Specific Objectives: (3 hours) Upon successful completion of this unit. Application Software c. Tree-Structured. Spooling). students should be able to: 1. Operating Systems Functions: a. Communications. explain multiprogramming explain timesharing describe the CPU – I/O burst cycle distinguish between preemptive and non-preemptive scheduling state the functions of the dispatcher list and explain at least three (3) scheduling criteria describe at least four (4) scheduling algorithms given a table with process data: Updated Jan 2010 Operating System Concepts Mrs. g. File Operations 2.Content: 1.
students should be able to: 1. 4. 6. describe the memory hierarchy describe the basic hardware used in memory management distinguish between logical and physical addresses explain swapping distinguish between contiguous and non-contiguous memory allocation explain partitioning describe the three (3) memory allocation strategies given a list of free holes and a list of processes. 2. 5. Memory hierarchy Basic memory hardware – base register. Priority. Time Sharing 2. 8. a. non-contiguous memory allocation Memory allocation strategies – first-fit. Preemptive scheduling. distinguish between internal and external fragmentation Content: 1. 7. j.i. 3. Shortest Remaining Time. Calculate the average wait time for each scheduling algorithm c. external (9 hours) Updated Jan 2010 (9 hours) UNIT V – Virtual Memory Operating System Concepts Mrs. worst-fit Partitions Fragmentation – internal. 3. Multiprogramming. 7. Scheduler. 8. Round Robin. physical address space Swapping Contiguous vs. Dispatcher 3. best-fit. Draw the GANTT chart for each process scheduling algorithm explain the advantages and disadvantages of each scheduling algorithm describe multiprocessor scheduling Content: 1. G. Multiple processor scheduling – Asymmetric & symmetric multiprocessing UNIT IV – Memory Management Specific Objectives: Upon successful completion of this unit. 4. Campbell Copyright @ 2010 9 . Scheduling algorithms – FIFO. Scheduling criteria 4. Scheduling concepts – CPU – I/O Burst cycle. b. 5. Shortest Job First 5. 2. limit register Logical vs. Calculate the turnaround time for each process for each scheduling algorithm. correctly allocate the processes to holes using the three (3) memory allocation strategies 9. 6.
distinguish between pure and demand paging 8. LFU e. Virtual address space 2. page table. define page 3. address translation 6.Specific Objectives: Upon successful completion of this unit. address translation 3. describe the various RAID levels Operating System Concepts Mrs. FIFO b. explain disk caching 7. explain segmentation 9. MFU f. state the advantages of disk caching 8. Demand paging 5. students should be able to: 1. 2. explain the term "virtual address space" 2. students should be able to: 1. define block describe the structure of a RAM disk describe the structure of an optical disk describe at least four (4) disk scheduling algorithms given a disk scheduling algorithm and a list of disk requests. explain thrashing Content: 1. use a diagram to explain and illustrate address translation in segmentation 10. Optimal replacement c. 5. define frame 4. Campbell Copyright @ 2010 Updated Jan 2010 (5 hours) 10 . LRU d. Segmentation – segment table. describe at least two (2) page replacement algorithms 7. 3. frames. 4. address structure. create the correct schedule to satisfy all requests 6. use a diagram to explain and illustrate address translation in paging 6. Pure paging – pages. explain the purpose of the page table 5. Page replacement a. G. Allocation algorithms 4. Thrashing UNIT VI – Auxiliary Storage Management Specific Objectives: Upon successful completion of this unit.
SSTF. Disk caching 7. explain the purpose of co-processors describe the characteristics of RISC architecture describe the characteristics of CISC architecture explain one advantage of RISC architecture explain one advantage of CISC architecture Content: Operating System Concepts Mrs. UNIT VII – File System Specific Objectives: (3 hours) Upon successful completion of this unit. log-structured systems 2. LOOK. C-SCAN 6. write. 4. Distributed file systems – naming. 3. G. Backup and recovery methods – full backup. 2. 4.Processor and RISC and CISC Specific Objectives: (1 hours) Upon successful completion of this unit. 5. students should be able to: 1. students should be able to: 1. 2. 3.Content: Blocks RAM and Optical disks Operations on moving-head disk – read. File server systems – client-server computing 3. positioning time. Campbell Copyright @ 2010 Updated Jan 2010 11 . SCAN. Disk scheduling – FCFS. positioning Measures of magnetic disk performance – transfer rate. incremental backup. location transparency. seek time rotational latency 5. RAID 1. 2. 5. 4. 3. location independence UNIT VIII – Co. explain at least two (2) backup techniques explain at least one (1) recovery technique describe file-server systems describe distributed file systems explain the advantages and disadvantage of a distributed file system Content: 1.
OS/2.. advantage. Apple Macintosh. Encryption. Common Coursework 20% 2. Operating systems concepts. Galvin. describe at least four (4) security threats and/or attacks 3. Final Examination 60% (40MCQ's 1 mark each and 5 Structured Questions 20 marks each to choose any 3) RESOURCE MATERIAL: Prescribed: Silberschatz. NJ: John Wiley Operating System Concepts Mrs. 5. disadvantage UNIT IX – Operating Systems Security Specific Objectives: Upon successful completion of this unit. 4. 3. 2. Windows (1hours) METHODS OF DELIVERY: 1.1. RISC / CISC – development. students should be able to: 1. & Gagne.B. G. discuss various ways in which operating systems handle security threats or attacks Content: 1. Campbell Copyright @ 2010 Updated Jan 2010 12 . worm. UNIX. Purpose of security Forms of security violation Security threats and attacks – Trojan Horse. Lectures Demonstrations Discussions Presentations METHODS OF ASSESSMENT AND EVALUATION: 1. Denial-of-service Authentication. Internal Tests 20% 3. 4. 3. (8th ed). logic bomb. define security 2. P. virus. A. Advantages and disadvantages of co-processors 2. Firewall Case Studies – MS-DOS. 2. Virus protection. G. (2008).
An introduction to operating systems. NJ: Prentice Hall.S. A. W. Operating System Concepts Mrs. Campbell Copyright @ 2010 Updated Jan 2010 13 . (2005).) OH: McGraw-Hill Stallings. W. NJ: Prentice Hall Shay.(6th ed.).). Modern operating systems (3rd ed. (2007). Operating systems: internal design principles (5th ed.Recommended: Tanenbaum. G. (1999).
MacOS. We do not use the computer because of these software. As new versions of the operating system are released. These are all examples of operating systems. play a game. video games. do our budget etc. word processors. I/O devices etc. Its primary goal therefore. A computer system is roughly divided into four (4) parts:• hardware .database systems. G. Unix. • users . Campbell Copyright @ 2010 Updated Jan 2010 14 .people. memory. surf the internet. machines.Lecture 1 – Introduction (1/2 hour) Microsoft Windows 7. business programs. Linux. DOS. The layers of a computer system Operating System Concepts Mrs. Without an operating system the user would have to communicate with the computer in binary form which would be very tedious and inconvenient. users upgrade their existing computers to the new version. • operating system (type of system software) • application software/programs . it typically has an operating system already installed. spreadsheets etc. We would however not be able to do these things on our computers without an operating system installed. We use the computer because we want to type a document. other computers etc. An upgrade usually costs less than purchasing the entire operating system. is to make the computer convenient to use.CPU. The operating system provides an environment in which a user may execute programs. Define operating system An operating system (O/S) is a program which acts as an interface between a user of a computer and the computer hardware. When you purchase a new computer.
or mobile computing device. An operating system is divided into the kernel and the superstructure. so no need to know which sector. command language. storage management. They can therefore be called multi-user operating systems. Windows XP. filing system. computers. track. Types/Categories of Operating Systems Operating systems fall mainly in 3 categories: Stand-alone. processor scheduling • always resident in memory once the computer is turned on • has a special area in memory reserved for it • superstructure • concerned with everything else • provides a user environment/interface that is convenient • basis of services to the user e. NT Workstation. 2000 Server). Campbell Copyright @ 2010 Updated Jan 2010 15 . Examples of network O/Ses include: Novell Netware. • kernel/monitor/supervisor/executive • concerned with the allocation and sharing of resources • interfacing to the hardware such as interrupt handling. and Linux. 95. and other devices to and from the network.g. OS/2 Warp Server for e-business. UNIX. ME). 98. Based on the diagram above it is clear that in order for the user to direct the hardware it does so through different layers. and Linux. data management (control of I/O devices. Microsoft Windows Server 2003. 200 Professional.g. Network and Embedded. OS/2 Warp Client. Mac OS X. A network administrator also uses the network O/S to administer network security. Stand-alone A stand-alone operating system is a complete operating system that works on a desktop computer. Network A network operating system organizes and coordinates how multiple users access and share network resources. notebook computer. Some stand-alone operating systems are called client operating systems because they work in conjunction with a network operating system. A network administrator uses the network O/S to add and remove users. G. mapping logical file structures onto physical devices. block) and job control. Early Microsoft Windows Server versions (NT Server. Operating System Concepts Mrs. 3.By itself. The hardware is capable of carrying out a wide variety of decisions and tasks in order to do this it needs to be given a set of instructions in a form that it can understand. Early Microsoft Windows versions (e. UNIX. the hardware is of as much use as a CD player without CDs. Stand-alone operating systems include DOS.x.
a multi-user system that combines batch processing. the background program is assigned to the processor whenever the foreground program is unable to proceed. research its new features and comment on them. 4. Campbell Copyright @ 2010 Updated Jan 2010 16 . Most modern operating systems are event/interrupt driven. in such a way that each user thinks he has a machine to himself.shares the processor and memory among a number of programs. 5. Tutorial Questions 1. Popular embedded operating systems include Windows CE . 2. One (the foreground) interacts with the terminal and runs as long as it is able. What are the main purposes of an operating system? What is the difference between the kernel and the superstructure? Describe the different categories of operating systems. time sharing and possibly transaction processing in a single system. • Time sharing . Practice MCQs 1.a single user system in which two programs are multiprogrammed. 6. Research the features of the operating systems mentioned. Controls the user c. G. 8. comment on its new features. E. However. If no. • Foreground background . Is controlled by application software d. 10. Differentiate between multi-user and multi-programming.g. Define operating system. Is there a difference between a multi-programming O/S and a multi-tasking O/S? 11. each associated with a remote interactive terminal. What operating systems are you familiar with? Have you ever used Windows 7? If yes.NET. Pocket PC 2002.the available processor(s) is shared among several programs coresident in main memory. what does this mean? 9. airline reservation system.Embedded Most PDAs and small devices have an embedded operating system that resides on a ROM chip. Give the name of five (5) operating systems.resembles a time sharing system in that it serves a number of remote terminals. and Symbian OS. all the terminals are connected to the same program. • General Purpose . Is no longer essential Operating System Concepts Mrs. Operating systems can also be categorized in the following ways" • Multi-programming . An operating system is a program that a. in order to improve CPU utilization. 7. 3. • Transaction processing . Gives instructions to the hardware b. Palm OS.
The part of the operating system that is always resident in RAM is called a. A. User. system software. application software. Hardware. Hardware B. Which of the following is TRUE for an operating system? a) It performs word processing tasks b) It is controlled by application software c) It provides a user interface d) It is inconvenient to use 5. G. Executive 4. application software d. Users Operating System Concepts Mrs. hardware. _____________ is an important part of a computer system that provides the means for the proper use of the computer resources. system software. hardware c. Select the correct sequence a. Operating System D. Fence d. Superstructure c. Segment b. Application programs C. application software. User.2. system software 3. User. application software. system software b. Campbell Copyright @ 2010 Updated Jan 2010 17 . hardware. user.
and left the programmer with a much more difficult debugging problem. take a dump (printout of errors in hexadecimal) if necessary. the operator was slow.g. it would return control to the resident monitor.usually the programmer set up a job by loading the card reader. There were still problems however. but take 60 seconds to be read by the card reader). the operator would have to notice this by observing it on the console. E. the operator . Efforts to remove the mismatch led to 2 developments: • introduction of I/O channel Operating System Concepts Mrs. The output from each job would be sent back to the appropriate programmer. If errors occurred then the programmer would halt the program. which would then go on to the next program. then started the program by manipulating switches on the console. Campbell Copyright @ 2010 Updated Jan 2010 18 . examine the contents of memory and registers and debug the program directly from the console. The relative slowness of the I/O devices meant that the CPU is often waiting on I/O. then load the card reader or paper tape reader with the next job and restart the computer. In the early days machines were hand operated. The operators would sort them into batches with similar requirements and as the computer became available. Initially when the computer was turned on. to process some cards by the CPU may take 4 seconds. that is. Another way of saving time was to batch the jobs together and run them through the computer as a group. Also as computer speed increased the ratio of set-up time to run time grew unacceptably out of proportion and the need arose to efficiently automate the job to job transition. These changes. I/O devices were slow. During the time that tapes were being mounted or the programmer was operating the console. would run each batch. an operator could start the next job. he would unload tapes.The history and development of the operating system Operating systems first began to appear in the late 1950s. At that time computer time was very expensive (about $45. control of the computer resided with the resident monitor. G. This monitor is always resident in memory. A small program called a resident monitor was created to automatically transfer control from one job to the next. as soon as one job was finished. When a job was done. Programmers would leave their programs with the operators. In those days machines were slow. the CPU sat idle. making the operator distinct from the user and batching similar jobs. remove the listing from the printer then set up the next job. when a job stopped. To overcome this: • automatic job sequencing was introduced.. Control cards were set up by the operator in order for the monitor to know the order in which jobs were to be run.g. which would transfer control to a program. improved utilization quite a bit. Eventually the programmer was replaced by professional computer operators. and with it the first rudimentary operating systems were created. mounting magnetic tapes etc. determine why the program stopped.66 per hour). During this transition from one job to the next the CPU sat idle. (E. when the program terminated.
and the one which became the most widespread in the late 1960s and early 1970s. input was transcribed from cards to magnetic tape and the program got its input by reading card images to tape and these were later transcribed to punch cards or the printer. when manufacturers introduced a new computer or model. This was achieved by job/CPU scheduling.e. By the mid 1960s multiprogramming was introduced. Operating System Concepts Mrs. In addition. Campbell Copyright @ 2010 Updated Jan 2010 19 . no changes need to be made to the application program to change from direct to offline I/O operation. WYLBUR. read data from tape and not from card). This ability to run a program with different I/O devices is called device independence. Once started the channel ran independent of central processor. IBM Time Sharing Option (TSO). Other early time sharing systems include: IBM CMS (part of VM/CMS). MUSIC/SP. The user's application software often would not work on the new computer because the programs were designed to work with a specific operating system. is toward deviceindependent operating systems that run on computers provided by a variety of manufacturers. The trend today. The first commercially successful time-sharing system. The main computer was therefore no longer constrained by the speed of the card readers and line printers. By 1970 multiprocessing. they often produced an improved and different proprietary operating system. A distributed operating system is one that appears to its users as a traditional uni-processor system. time sharing and data communications (network operating systems) were introduced. Having several jobs in memory at one time requires memory management. A devicedependent program is one that runs only on a specific type or make of computer. The mid 1980s also introduced distributed operating systems. however. The users should not be aware of where their programs are being run or where their files are located. Time sharing allowed immediate access to all of the application programs that were running. G. (i. Historically. high level user oriented programming languages. Problems arose when a user wanted to switch computer models or manufacturers. Most of the first operating systems were device dependent and proprietary. was the Dartmouth Time-Sharing System (DTSS) which was first implemented at Dartmouth College in 1964 and eventually formed the basis of General Electric's computer bureau services. Michigan Terminal System. but only by the speed of the magnetic tape units. Time sharing used CPU scheduling and multiprogramming to accomplish this. Proprietary software is privately owned and limited to a specific vendor or computer model. On into 1980s came interactive real-time systems that enabled on-line communication between the user and the computer. in which the CPU switches to another job instead of sitting idle waiting on I/O. • introduction of the technique of "off-lining" I/O instead of the computer using the slow peripheral devices directly. The user could now give instructions via commands instead of control cards. Some operating systems still are device dependent. Multics. Only the device driver must be changed. this allowed the simultaneous processing of more than one program at a time.a piece of hardware to control I/O devices in an autonomous manner. even though it is actually composed of multiple processors.
based on General Motors Operating System IBSYS (IBM) CTSS (MIT) MCP (Burroughs) OS/360 (IBM) Dartmouth Time Sharing System Multics (MIT. G.0 Mac OS (System 1.0 Windows NT 3. This feature usually represents a sizable savings in time and money. Bell Labs) DOS/360 (IBM) CP/CMS (IBM) Unics (later Unix) (AT&T) DOS-11 (PDP-11) VM/CMS CP/M Cray Operating System Xenix PC-DOS MS-DOS Novell NetWare (S-Net) SunOS 1.0) OS/400 BeOS (v1) Linux Mac OS (System 7) Solaris 2. GE.0 OS/2 (1.1 Novell NetWare 4 Windows 95 Updated Jan 2010 20 .The advantage of device-independence is that you can retain existing application software and data files even if you change computer models or vendors.0 SunOS 3. Decade 1950s Year 1954 1955 1956 1960s 1960 1961 1964 1965 1966 1967 1969 1970s 1970 1972 1975 1976 1980s 1980 1981 1983 1984 1986 1987 1988 1990s 1990 1991 1992 1993 1995 Operating System Concepts Mrs. The following table lists some of the operating systems that have been developed over the years.0) AIX 1. Campbell Copyright @ 2010 Sample of Operating Systems MIT's operating system made for UNIVAC 1103 General Motors Operating System made for IBM 701 GM-NAA I/O for IBM 704.
Who invented it? Describe the situation that most impacted the development of operating systems. Which of the following greatly impacted the development of the operating system? a) The CPU was slow compared to the operator Operating System Concepts Mrs.0 Palm OS Windows 98 Mac OS 9 RISC OS 4 Windows 2000 Solaris 8 Windows ME Mac OS X Windows XP SUSE Linux Windows Server 2003 Ubuntu 5. What generation do the different operating systems belong to? Practice MCQs 1.5 Solaris 10 5/08 SUSE Linux 11. In your description include the names and features of the older operating systems. 2. G. One factor that led to the development of operating systems was that a) The CPU was often idle b) The I/O devices were too fast c) Programmers could not debug problems d) The CPU was overworked 2. 4. Describe the historical development of operating systems.2 FreeBSD 8.10 Mac OS X v 10.0 Windows 7 Windows Server 2008 R2 openSUSE 11. Campbell Copyright @ 2010 Updated Jan 2010 21 .0 2001 2002 2003 2005 2006 2007 2008 2009 Tutorial Questions 1.6 Windows NT 4. Discuss the first operating system. Describe the historical development of operating systems from 1980 to the present. 3. 6.04 Windows Vista Ubuntu 7. Describe the features of as many operating systems as you can.1996 1998 1999 2000s 2000 Mac OS 7. 5.
G. First Generation B.b) The CPU was often idle c) The CPU was overworked d) The CPU was slow compared to I/O devices 3. In what time period was the first operating systems developed? A. Fourth Generation Operating System Concepts Mrs. Third Generation D. Campbell Copyright @ 2010 Updated Jan 2010 22 . All of the following describe ways in which designers dealt with the difference in speed between the CPU and I/O devices EXCEPT: a) Multi-programming b) I/O channel c) Off-lining I/O d) Buffering 4. Second Generation C.
which is firmware with the computer's startup instructions. Booting is the process of starting or restarting a computer. When a user turns on a computer. If the POST completes successfully. requests any necessary user information.Lecture 2 .Operating Systems Functions (1 hour) Functions Most operating systems perform familiar functions that include the following: • Start up or boot up the computer • Provide an interface between the hardware and the user that is more convenient than that presented by the bare machine. single user/multitasking. and displays the desktop. multiuser. The BIOS performs the power-on self test (POST) to check system components and compares the results with data in a CMOS chip. the power supply sends a signal to the system unit. A single tasking operating system can run one program at a time. an operating system can support at one time. the BIOS searches for the system files and the kernel of the operating system. The processor chip finds the ROM chip(s) that contains the BIOS. Finally. This is done on a network. Memory management optimizes the use of RAM. • Manage other programs • Manage memory • Control/Co-ordinate/Configure the various hardware devices • Manage the sharing of resources (such as two persons trying to print at the same time on a network) • Schedule jobs • Establish an internet connection • Monitor performance • Provide file management and other utilities Some operating systems also allow users to control a network and administer security. the operating system loads configuration information. and how many programs. An operating system can be single user/single tasking. the operating system may use virtual memory. Managing programs refers to how many users. Campbell Copyright @ 2010 Updated Jan 2010 23 . A multi-user operating system allows more than one person to use the computer at a time. A multitasking/multiprogramming operating system can run more than one program at the same time by scheduling the processor's time. A single user operating system allows only one person at a time to use the computer. Operating System Concepts Mrs. If memory is insufficient. G. which manages memory and devices. or multiprocessing. A multiprocessing operating system is where more than one processor is used to run more than one program at the same time. and loads them into memory from storage. which allocates a portion of a storage medium to function as additional RAM.
File management utilities (such as Windows Explorer [Do not confuse this with Internet Explorer – a web browser]) allows the user to copy files. A command line interface is where a user types commands or presses special keys on the keyboard (such as function keys) to enter data and instructions. Campbell Copyright @ 2010 Updated Jan 2010 24 . With a graphical user interface (GUI). move files. What is a Menu driven interface? A menu-driven interface provides menus as a means of entering commands. grammar and punctuation. Many current GUI operating systems incorporate features similar to those of a Web browser. Command-line interfaces however. A job is an operation the processor manages. Operating System Concepts Mrs. A performance monitor is an operating system program that assesses and reports information about computer resources and devices. All hardware devices are managed and scheduled among the various jobs or programs that are run. G. generate an error message. What is a User Interface? The user interface controls how data and instructions are entered and how information is displayed. Scheduling is done via a scheduling algorithm. delete files and create folders. menu-driven interface. give a user more control over setting details. Minor errors such as a missing full stop. Three types of user interfaces are command-line interface. Menu driven interfaces are easier to learn than command line interfaces because users do not have to learn the rules of entering commands. Configuring devices involves loading each device's driver when a user boots the computer. you interact with menus and visual images such as icons. and graphical user interface. As in a restaurant. When working with a command-line interface the set of commands entered into the computer is called the command language.Scheduling jobs determines the order in which jobs are processed. Establishing an Internet connection sets up a connection between a computer and an Internet service provider. network administrators and other advanced users work with a command-line interface. What is a Command driven or command line interface? To configure devices. A driver is a program that tells the operating system how to communicate with a specific device. Command line interfaces often are difficult to use because they require exact spelling. What is a Graphical user interface (GUI)? Most users today work with a graphical user interface. a menu is a list of items from which you may choose and option. buttons and other graphical objects to issue commands. manage resources and troubleshoot network connections.
The CPU is therefore free to carry on with other work while the spool file is being created. In disk systems. An area in memory being used for data awaiting processing or output is called a buffer area. the entire tape had to be written before it was rewound and read. The problem with tape systems is that the card reader could not write onto one end of the tape while the CPU read from the other. It attempts to keep both the CPU and the I/O devices busy all the time. Operating System Concepts Mrs.Services An operating system provides an environment for the execution of programs. By moving the read/write head from one area of the disk to the other. This section deals with some of the common services provided by operating systems. is satisfied by reading from the disk. the print line is copied into a system buffer and written to the disk. After data is read and the CPU is about to operate on it the input devices are instructed to begin the next input immediately. Campbell Copyright @ 2010 Updated Jan 2010 25 . Requests for card reader input. Output devices are slow compared to processing so in order to keep the CPU busy with processing and not waiting on an output device to finish before it can move on. the data is put in a buffer (in fraction of the time) rather than being put straight to a slow output device. The CPU and input devices are therefore both busy. Services provided differ from one operating system to the other. An output buffer accepts data at a high (electronic) speed from the CPU and releases it at the slower speed of the output device. the disk can rapidly switch from one card to another. G. Buffering is therefore the solution to the slowness of I/O devices. The CPU can then move on to do other things. Disk systems eliminated that problem. When the job/program is completed then the output is actually printed. The O/S provides certain services to programs and the users of the programs. cards are read directly from the card reader onto the disk. An input buffer accepts data from a slow speed device at a slow speed but releases it at high speed to the CPU. Similarly when a job requests printer output. Data is put into a buffer (memory) until the output device can accept it. It puts the output to the disk in the form of a spool file instead of to the printer. Spooling (Simultaneous Peripheral Operation On-Line) This method was invented at Manchester University in England. It therefore uses the disk as a very large buffer. The location of the card is recorded in a table and is kept by the operating system. These services are functions that are provided for the convenience of the programmer. Buffering A buffer is high speed storage (memory). A buffer can be a reserved section of primary storage or can be located on the I/O device itself.
One protocol is that the job requests all the resources that it needs at the start. the operating system may take resources from a job (i. the operating system should allow creation and deletion of such files. To prevent deadlock. either normally or abnormally. Another protocol allows a request from a job only when it has no resources. Hold and wait .ensure that at least one of the following conditions does not hold.g. Operating System Concepts Mrs. then each will wait for the other to release its tape drives. • File System Manipulation Programs need to read from and write to files.e. mutual exclusion .when a process requests a resource it does not hold another resource. • Deadlock Prevention/Recovery This is a situation where waiting processes stay permanently in a wait state because other waiting processes are holding the resources that they have requested. Campbell Copyright @ 2010 Updated Jan 2010 26 . which will never happen unless the operating system steps in. The program must be able to end its execution. All 4 conditions must exist for deadlock to occur. terminate process). or recover from one. Each resource is either currently assigned to exactly one process or is available. • Input/Output Operations A user program cannot execute I/O operations directly.Other Services • Program execution The operating system loads a program into memory and runs it. Deadlock prevention . Example:. 1.If there are 4 tape drives and 2 processes and each process holds 2 tape drives but needs 3. A printer cannot be shared simultaneously). Processes currently holding resources granted earlier can request new resources. Pre-emption of resources. G.must hold for non sharable resources (e. the operating system must provide some means to do so. (a read only file is sharable) 2.
jam in the card reader etc. What are some of the services provided by an operating system? Practice MCQs 1.of resources that have already been allocated. Describe the conditions for deadlock. name and discuss a method by which the operating system is able to correct the imbalance between the speed of the CPU and the I/O devices. All of the following are services provided by an operating system EXCEPT: a) File system management b) Buffering c) CPU scheduling Operating System Concepts Mrs. All of the following are conditions for deadlock except: a) Circular wait b) Pre-emption c) Hold and wait d) Mutual exclusion 2. Describe how the banker's algorithm works. Circular wait . With the aid of a diagram. Campbell Copyright @ 2010 Updated Jan 2010 27 . State three (3) functions of an operating system.3. 7. Tutorial Questions 1.each job is assigned a number as to who gets a resource next (linear ordering . List examples of deadlock which are not related to a computer system environment. memory. 4.each process can request resources only in increasing order). Resources previously granted cannot be forcibly taken away from a process. 5. 3. • Protection So that one job does not interfere with the others. • Error Detection/Troubleshooting The operating system constantly needs to be aware of possible errors. The operating system should be able to take the appropriate action. No pre-emption (No taking away) . G. They must be explicitly released by the process holding them. • Accounting To keep track of which users use how much of what kinds of computer resources. each of which is waiting for a resource held by the next member of the chain. 6. 2. • Resource Allocation This is due to multiple users or multiple jobs running at the same time. To reconcile conflicting demands. There must be a circular chain of two or more processes. Errors may occur in the CPU. How does buffering differ from spooling? 4.
A. Scheduling 5. buffer C. One of the services provided by an operating system is deadlock prevention. Paging C. G. cache D. ____________ allows you to send a second job to the printer without waiting for the first job to finish printing. A.d) Record management 3. A __________ is an area of memory or storage in which data and information is placed while waiting to be transferred to or from an input or output device. Spooling B. Campbell Copyright @ 2010 Updated Jan 2010 28 . RAM B. registers Operating System Concepts Mrs. What is deadlock? a) A user is locked out of a program due to insufficient authority levels b) A job recovers from hanging and reboots slowly c) A job is in a permanent wait state due to another job holding a needed resource d) A computer hangs because the kernel is overwritten 4. Thrashing D.
g. Examples include: accounting. when to do it. Linux.Lecture 3 . • File compression – Reduces the size of a file usually to a ZIP extension.g. create graphs. do our accounting. E. E.g. E. OS/2. Quickview in Windows. spreadsheet. NovaBACKUP • Anti-virus – Prevents. Application software is the user's reason for using the computer.g. The opposite RESTORE utility should also exist in order to recover the files in case of loss/damage. defrag in Windows • Backup – Copies selected files to another disk/tape. Example of a physical problem – scratch on disk. AVG etc. McAfee. we use the computer to type documents. E. MSBACKUP. E. Utilities provide a useful service to the user by providing facilities for performing common tasks. Example of a logical problem – corrupted file. We do not use the computer because we want to use Microsoft Windows 7. The following are examples of utilities: • File viewer – Displays the contents of a file. The following are examples of types of application software: Operating System Concepts Mrs. word processing.g. Campbell Copyright @ 2010 Updated Jan 2010 29 . System Software There are two types of system software: operating system and utility. an operating system consists of the programs that control or coordinate the operations of a computer and its devices. G. Unix. DOS etc. WinZip. In other words software is any instruction that tells the computer what to do. removes viruses from a computer system. detects. There are two types of software: system software and application software. play games etc.Software and Firmware (1/2 hour) This topic is mostly revision as it was already covered in the course Fundamentals of Information Technology. draw pictures. As mentioned before. Software is a collection of machine interpretable instructions that define the activities related to performing a specific task by computer. PKZIP. Scandisk. Examples include: Microsoft Windows XP. banking. • Diagnostic utility – Compiles technical information about your computer hardware and reports physical and logical problems. • Defragmenter – Reorganizes files and unused space on a disk so that data can be accessed quickly and programs run faster. database management. The software that allow us to do these things are application software. E. Application software Application software is designed to fulfil a specific set of activities. Norton Anti-virus. enter data into a database. graphics. Trend Micro PC-cillin.g. WinRAR. It alerts you if an additional disk is needed. Operating systems tell the computer what to do and how to do it. Norton disk doctor.
g.g. C.a large piece of paper divided into columns and rows into a grid of cells. Lotus 1-2-3. footnotes. formulas. margins. Multiplan • Database Management Information is vital to business. People called programmers use programming languages to tell the computer what to do. print. Field. font size and type. Symphony. Database management software allows you to create and maintain a database. mail merge. Solitaire etc. Windows Media Player. Requires a lot of main memory and usually special circuit board (graphics card) and a high resolution screen. and information or c) provide an interface for users to communicate with one another. A database is a collection of organized of information stored in a way that makes it easy to find and present. fieldsize. Outlook (Email). many companies insist on using the most common languages so they can take advantage of programs written elsewhere and to ensure that their programs are portable. E. which means that they will run on different computers.Bold.g. User can enter numbers. Quattro Pro. fieldtype.g. instructions. Monopoly. etc. newsletters. table of contents. Features include:. software that allows you to listen to music of watch movies. E. Foxpro. spell check. Wordstar. printing of documents. WordPad. • Entertainment software These software include games. E. E. E. Combine word processing and graphics packages. justify. WordPerfect. query. Microsoft Publisher • Graphics Provide facilities that allow user to do various kinds of computer graphics. Communication software allows users to send messages and files from one location to another.• Word-processing Allow easy creation.g. save. Web Browsers. editing. text in each cell. underline.g. COBOL etc. Campbell Copyright @ 2010 Updated Jan 2010 30 . Microsoft Access • Desktop Publishing To produce documents. Oracle. E. Chess. Netscape Navigator. Dbase. keys. Visi-Calc. G. page number. However. Most were developed for writing specific types of applications. E.g. Pascal. C++. Outlook Express. Microsoft Word. Can sort. Visual Basic.g. AmiPro • Spreadsheets Designed to manipulate numeric data in a tabular form. Adobe Photoshop • Programming languages/program development software Used to create programs. correction. E. Network Operating Systems (NOS). posters. This is the electronic equivalent to accountant's ledger . Operating System Concepts Mrs. Microsoft Excel. Corel Draw. Foxpro. Page Maker. • Communication Software This is any program that a) helps users establish a connection to another computer or network or b) manage the transmission of data. Hundreds of programming languages or language variants exist today.
Firmware are programs held in ROM (i. Lotus Smartsuite. Tutorial Questions 1. E. This is made with CMOS (complementary metal-oxide semiconductor) technology. They are stored permanently in ROM and are ready when the computer is switched on. Notepad)? Operating System Concepts Mrs. diskette drive. printer port. When you turn on a computer: • Run BIOS programs (basic input output system) checks hardware . cd-rom drive. MS-Word) differ from a text editor (e. E. 2.g. e) A publishing house who wants to produce a magazine. Differentiate between system software and application software. How does a word processor (e.• Integrated Packages Collections of packages which have been designed to be used together. For mainframes etc. The processor immediately starts to execute the instruction in firmware.g. E. a) Preparing a letter to a customer. Campbell Copyright @ 2010 Updated Jan 2010 31 .e. the area on device is specific to the manufacturer. Corel Wordperfect Suite. serial ports (modem) • Loads operating system (usually independent of the machine) must look at particular address (ie goes to booting device) For PCs operating system must be on track 0. b) A teacher calculating student grades. On smaller machines the 2 programs may be combined into a single program called a monitor. Microsoft Office. Spreadsheet data might be easily fed into a database or displayed in a diagrammatic form using a graphics package. When you turn on a computer the first thing that tells the computer what to do is firmware. keyboard. location 0. Firmware therefore facilitates booting. Normally a special control program is loaded which in turn loads and runs a program called a command interpreter or shell. 3. hard-coded in the hardware). Open Office.monitor. On a small microcomputer based system the firmware ROM normally containing a special 'loader program' to load a program into memory from the floppy disk. G. When the computer is switched on a control signal is sent to the microprocessor which causes it to reset its current instruction register to the location address of a firmware instruction. d) A human resource manager who wants to perform various queries on employee data. Give examples of the type chosen. Firmware Firmware is also known as micro-code or micro-program. The reset control signal takes place as part of the switching on operation. memory. hard disk. Identify the type of application software that would be best suited in the following situations.g.g. c) A financial controller making a speech to the shareholders of a company. mouse. sector 0 of boot disk. This is software embedded in hardware.g.
[Make sure that you include the ones made for mobile devices] Practice MCQs 1. 5. Antivirus software Operating System Concepts Mrs. 6. What are the two types of system software? a) Application software and operating system b) Utility and application software c) Utility and operating system d) Special purpose and general purpose 4. Research the various web browsers. What are the utilities that you have used? Comment on them. Scandisk b. Which of the following is TRUE about application software? a) It provides a user interface b) It allows the user to perform a specific task c) It is in charge of the utility programs d) It controls the hardware 3. Utilities D. Restore c. 8. How does software differ from firmware? Give examples of how firmware is used. Anti-virus d. System software C. All of the following are TRUE statements about firmware EXCEPT: a) Assists in the booting process b) Programs held in the boot sector c) Forms a part of the operating system d) Programs held in ROM chips 6. ______________ consists of programs that control the operations of the computer and its functions.4. Which of the following types of system software provides a maintenance function? a) Application software b) Utility c) Operating system d) Special purpose 5. G. A. 7. Defrag 2. The utility that is always provided with a backup utility is a. Do some research and describe other popular utilities. Campbell Copyright @ 2010 Updated Jan 2010 32 . Application software B.
Diagnostic 9. Disk scanner C. Disk cleanup B. ____________ utility compiles technical information about a computer's hardware and certain system software programs and then prepares a report outlining any identified problems. Diagnostic utility D. A. Disk scanner C. Disk defragmenter B. ____________ is a utility that reorganizes the files and unused space on a computer's hard disk so that data can be accessed more quickly and programs can run faster. Disk cleanup Operating System Concepts Mrs. A. Campbell Copyright @ 2010 Updated Jan 2010 33 . G.7. Disk defragmenter D.
msdos. For convenient use the operating system provides a uniform logical view of information storage. the file.sequence of subroutines and functions object/executable file . The operating system implements the abstract concept of a file by managing storage devices such as tapes and disks. Campbell Copyright @ 2010 Updated Jan 2010 34 . A read-only file is any file with the read-only attribute turned on.ini. It is a sequence of bits. hidden. io.sys. Operating System Concepts Mrs. last modified. The owner decides on the file operations allowed and by whom.sequence of characters organized into lines (and possibly pages) . COM graphics files . write. The operating system abstracts from the physical properties of its storage devices to define a logical storage unit. bytes. It has other properties such as its type. A file is a named collection of related information usually saved on secondary storage. It is mapped onto a physical device. File attributes are maintained in the directory structure. its length etc. but Windows will prompt you with a special dialog box asking you to confirm that you want to move or delete the read-only file. A file is named and is referred to by its name. system. It is a characteristic of a file. Common File types:text file . DBF etc.sequence of words organized into loader record blocks – EXE. In MS-DOS. abstracting out the physical properties of the storage device. execute • Ownership – who owns the file.File concepts (1 hour) Files store data and programs. • Type – some operating systems support different file types and handles them differently • Location – information on the device and location of the file data • Size – current size of the file (in bytes) • Various dates – date created. OS/2 and Microsoft Windows the attrib command can be used to change and display file attributes. BMP.Lecture 4 . compressed. A file is a collection of related information. In other words. archive. last accessed • Protection – access control – who is allowed to read.JPG. date and time of creation. File Attributes A file has the following attributes: • Name – a string of characters that identifies the file. Read-only files can be deleted and moved. A file is a logical entity which represents a named piece of information.sys. A read-only file can be viewed. Files are normally organized into directories (folders) for ease of use. A file attribute (or just attribute) is a specific condition in which a file or directory can exist. TIF database file – MDB. Examples include read-only. Some common files that are readonly by default in Windows include boot. A file with the readonly attribute turned on can be opened and accessed normally by your computer. G. but not changed. It is a logical storage unit.TXT source file . "writing" to the file is disabled. records.
File Operations A file is a means of storing information for later user. Most Windows computers are configured by default not to display system files in normal file searches or in folder views. working with a file that is compressed will use more processor time than working with an uncompressed file because Windows has to decompress and then recompress the file during use. ntdetect.sys. A compressed file is any file with the compressed attribute turned on.sys. io. The most popular system files you might encounter on a Windows computer include msdos. To avoid constant searching most operating systems keep a table of open files. Since most computers have plenty of hard disk space. compression isn't usually recommended. The archive attribute is usually turned on when a file is created or modified. Return integer (file descriptor) if permitted. copy file to an I/O device (printer.com and ntldr. 2. Once the file is backed up by a backup program. Return error code if not. append new information to the file • create a copy of a file. A system file is any file with the system attribute turned on. especially since the trade off is an overall slower computer thanks to the extra processor usage needed. What the Operating System must do for each of the 5 basic file operations NB. An archive file is any file with the archive attribute turned on. write to the file. operating system and other control program files are marked as System files as a means of identification. However.ini. Any file can be marked as Hidden. Some of the things we would want to do are:• create a file. Campbell Copyright @ 2010 Updated Jan 2010 35 . The most popular hidden files you might encounter in a Windows system include msdos. Most Windows computers are configured by default to display compressed files in blue text in normal file searches and in folder views. Open a file Check permissions. When finished with a file Close it. Files marked Hidden and System do not normally display unless the file manager option to display them is selected.A hidden file is any file with the hidden attribute turned on. the backup program can use the archive attribute to determine which files have changed and need to be backed up and which have not changed and do not need to be backed up. Creating a file Operating System Concepts Mrs.sys. the archive attribute is turned off. display). Most Windows powered computers are configured by default not to display hidden files in normal file searches.sys and boot. delete the file • edit/modify the file. 1. Many files that you'll encounter in normal computer use will likely have the archive attribute turned on. This way. read from the file. however. Before you can use a file you must Open it. io. G. rewind the file. rename a file etc. The archive attribute is used for backup. Setting the compressed file attribute on a file will reduce the size of the file but will allow Windows to use the file just as any other.
com. Campbell Copyright @ 2010 Updated Jan 2010 36 . Describe the type of file. directory entry has stored a pointer to current end of file using this pointer the address for the next block is computed and the information can be written. Truncate Maintains file attributes but erases the content of the file. 4. Practice MCQs 1. Make an entry in the directory (directory entry records name/location of file) 3. 4. A file is a) A collection of directories Operating System Concepts Mrs. bmp). Describe five file operations. Append Writes information to the end of the file. Tutorial Questions 1. Writing to a file (must be opened as output) 1. system call must specify name of file and the information to be written. 2. 3. 2. Describe five file attributes. Suppose systems automatically open a file when it is referenced for the first time and close the file when the job terminates. then the write pointer is updated.Find space on the file system. 3. exe. system searches directory to find location of file. Reading a file (open as input) specify name. When the next block is to be read the pointer to next block is updated. Make a list of as many file types that you can (e. Delete Release file space and erase the directory entry so that it can be reused by other files. doc. Other file operations include: Rewind (only with tapes) Current file position pointer is reset to the beginning of the file.g. Discuss the advantage and disadvantage of this scheme as compared to the scheme when the user has to explicitly open and close the file. System specifies where in memory the next block of the file should be put. 5. G. jpg. Seek Repositions the location pointer for the file.
Which of the following is NOT a file attribute? A. G. Truncated D. Name B.b) A group of application programs c) A mapping of the physical properties of a storage device to a logical storage unit d) A group of related databases with minimum duplication and redundancy 2. Identifier C. Location Operating System Concepts Mrs. Campbell Copyright @ 2010 Updated Jan 2010 37 .
therefore they would take up a small amount of tape. size and type for all files on that device. not physical. but it suffers from some inefficiency. These are all directory operations. Directory Operations Directory operations are those actions performed on a directory by a user. The directory lists the name and location of each file on the tape. G. Just think of all of the things that you can do in MyDocuments or Windows Explorer. A directory structure organizes and provides information about files on the system. A file can be on more than 1 disk. To handle this problem. A directory is therefore similar to a table of content or index in a text book.Directory Systems (2 hours) Early file systems were tape based. location. creation date.400 feet). Campbell Copyright @ 2010 Updated Jan 2010 38 . The device directory records information such as name. since physical tape reels are quite large (e.Lecture 5 . Studies showed that most files were small. The following describes the different directory systems: Operating System Concepts Mrs. They include the following: • • • • • • • • Search for a particular file Create a file Delete a file Rename a file Create directory List directory Traverse the file system Backup Nowadays. The advantage of this approach is simplicity. There was a problem in determining which files were on which tape. Directory Systems Types of directories/directory structures The term directory system can also be referred to as type of directory or directory structure. directories are known as folders and are identified by a folder icon . The table of content or index is used to location specific chapters or topics. This allows the file to be easily located. Directory structure provides a mechanism for organizing the many files on the file system. but the user only has to worry about logical directory and file structure. To solve this problem a directory was added to the tape.g. systems were created to store multiple files on one tape. Each file was implemented by mapping it onto its own reel of tape. 2.
system files and grouping files. When a user lists the directory he sees only his files. to a specified file. Allows users to create their own subdirectories and organize their files accordingly. This isolates one user from another. A file name is prefixed by user name. Two level – There is one master file directory but a separate directory per user. Windows. grouping and other operations such as deleting. It however has significant limitations in terms of the naming of a large number of files as well as supporting different users and topics (groups). UNIX. All files must have unique names.g. All files are in the same directory. There are limitations in terms of sharing files with other users. If a file is needed which is not in the current directory. Each entry in the master file directory points to a user file directory. Campbell Copyright @ 2010 Updated Jan 2010 39 . Users may also create their own subdirectories. DOS. G.e.Single level . A path name is the path from the root through all the subdirectories. Tree. It is easy to support and understand.structures . The current directory should contain most of the files that are of current interest to the user. then the user must either specify a path name or change the current directory. Every file has a unique path name. Operating System Concepts Mrs. This structure is efficient for searching. each user has a current directory.the simplest directory structure. In normal use. The tree has a root directory.
This occurs in cases where two users need to use a common directory as their own directory. Campbell Copyright @ 2010 Updated Jan 2010 40 .EXAMPLE OF A TREE DIRECTORY STRUCTURE The diagram shows that the path to file D is ROOT\DIRECTORY2\DIRECTORY2A Acyclic Graph . Changes made by one user to the file are viewed immediately by the other user. The following is an example using Unix.A shared directory or file exists in the file system in two (or more) places at once. The same file may be in two different directories (i. This directory system therefore allows for the sharing of directories and files. Symbolic links Operating System Concepts Mrs. Note that files have multiple path names. G. EXAMPLE OF AN ACYCLIC GRAPH DIRECTORY STRUCTURE The diagram shows that file D has multiple paths which are:ROOT\DIRECTORY2\DIRECTORY2A and ROOT\DIRECTORY1 There are different ways in which acyclic graphs (shared files and directories) are implemented.e. therefore distinct file names may refer to the same file. can be access through more than one path). It is not the same as two copies. NB.
Problem: What happens when the original file is deleted? Duplicate directory entries (also called hard links) • The original and copy entries are the same • Problem: What happens when one deletes the original or copy entries? Tutorial Questions 1. Practice MCQs 1. Which of the following directory systems allow files to be in more than one directory at the same time? a) Single level b) Two level c) Tree d) Acyclic 4. A two-level directory structure a) Has a root directory and two subdirectories b) Is the most complex directory structure c) Has two files in each directory d) Has a separate directory per user 2. Compare and contrast FAT with NTFS.• • • • A different type of a directory entry (other than a file or a directory) Specifies the name of the file that this link is pointing to Can be relative or absolute. G. How does it deal with the problems of the acyclic graph directory? 2. NTFS). Research the General-Graph directory. Research on the various filing systems (such as FAT. Which of the following directory systems have a separate directory for each user? a) Single level b) Two level c) Tree d) Acyclic 3. All of the following are TRUE for the tree structure EXCEPT: a) Files are organized into directories and sub-directories b) Changes made by one user of the file is viewed immediately by the other user c) Every file has a unique path name d) Duplicate file names are seen as different files Operating System Concepts Mrs. 4. Differentiate between the tree structure and the acyclic structure. 3. HPFS. Campbell Copyright @ 2010 Updated Jan 2010 41 .
file pointers. a tape. G.Multi-programming and TimeSharing (1 hour) Multi-programming A single user cannot keep either the CPU or the I/O devices busy at all times.).g. for an I/O device). but in a multi-programmed environment the CPU will switch to another job. By switching between processes the operating system can make the computer more productive. The basic idea is that the operating system picks one of the jobs in the job pool and begins to execute it. Campbell Copyright @ 2010 Updated Jan 2010 42 . Memory management software keeps track of the jobs being run. The basis of the multi-programmed operating system is that by switching between jobs the CPU becomes more productive. normally the CPU would sit idle. In a multi-programmed environment the operating system would switch to another job. Eventually the job may have to wait for something (e. Eventually the job may have to wait for something. another job can be using the CPU. keyboard input etc. Multiprogramming or multi-tasking is an attempt to increase CPU utilization by always having something for the CPU to execute. addresses etc. This is also called concurrent processing.e. (i. variables.Lecture 6 . The operating system picks one of the jobs in the job pool (ready queue) and begins to execute it.g. Normally the CPU would sit idle. Process State Diagram Updated Process State Diagram While one job is waiting (e. Process images) so that movement between the disk and main memory is Operating System Concepts Mrs. the current instruction.
file pointers etc. Tutorial Questions 1. program counter. information associated with each process. 3. What are the main advantages of multi-programming? 2. values in variables. The Process Control Block (PCB) has the process state. Ready Operating System Concepts Mrs. G. The location of current instructions. CPU scheduling information. This communication is called interprocess communication (message passing). and I/O status information. In other words. Related processes that are co-operating to get some job done often need to communicate with one another and synchronize their activities. memory management information. New B.transparent to the user and so that the job can be restarted at the same state at which it was stopped. Which of the following process states indicates that the process is waiting to be assigned to the processor? A. CPU registers. Memory management software should also protect the operating system and the Job in that the Process/Job should not be placed in an area in memory reserved for the kernel. Running C. accounting information. Practice MCQs 1. What is the purpose of multi-programming? a) To improve the process state b) To prevent deadlock c) To perform aging d) To increase CPU utilization 3. Waiting D. Campbell Copyright @ 2010 Updated Jan 2010 43 . Describe the operation of the PCB. form part of a) Interprocess communication b) Kernel c) Ready queue d) Process image 2. Differentiate between a process and a program.
while multitasking more broadly encompasses the simultaneous execution of multiple processes.Time Sharing Time-sharing is an approach to interactive computing in which a single computer is used to provide apparently simultaneous interactive general-purpose computing to multiple users by sharing processor time. Operating System Concepts Mrs. Computers capable of providing time-sharing services would usually operate in batch mode overnight. small slices of time spent waiting for disk. it was suggested that multiple users could share a machine by using one user's idle time to service other users. Differentiate between multi-programming and time sharing. In order to provide smooth service to multiple users. Because early mainframes were extremely expensive. however. G. This required a hardware interrupt system capable of pausing a running process. or network input could be granted to other users. These solutions alone were not sufficient to build a fully functional time-sharing system. Tutorial Questions 1. regardless of the number of users. But because computers in interactive use often spend much of their time idly waiting for user input. a time-sharing system needed a way to deal with multiple processes that did not frequently pause for input/output. it was not possible to allow a single user exclusive access to the machine for interactive use. and giving processor time to another process. Campbell Copyright @ 2010 Updated Jan 2010 44 . Time-sharing. Similarly. refers to a computer supporting multiple simultaneous users. tape. Time-sharing is related to multitasking in that both systems involve a single computer processor executing multiple processes in an apparently simultaneous manner.
The following defines various scheduling concepts. algorithms (6 hours) Scheduling concepts In order for multi-programming to take place. the different programs need to take turns in using the processor.8 Store z CPU burst Wait for I/O I/O burst . Scheduling is done via scheduling algorithms which will be discussed later. CPU – I/O Burst Cycle . Read from file add x to amount } } } } } } CPU burst Wait for I/O I/O burst Store y Write to file CPU burst Wait for I/O I/O burst Multiply by 16. Ready Queue/Job Queue – holds a list of jobs/processes which are ready and waiting to execute.Lecture 7 . criteria. . . G. Campbell Copyright @ 2010 Updated Jan 2010 45 . An example is shown in the diagram below.Scheduling concepts. . . The programs therefore have to be scheduled. Operating System Concepts Mrs.determines which jobs are admitted to the system for processing and loads them into memory. Long Term Scheduler/Job Scheduler .Process execution that consists of a cycle of CPU execution and I/O wait. .
4. Dispatch latency is the time that it takes for the dispatcher to stop one process and start another. intermediate level of scheduling. 2. It controls the degree of multiprogramming (the number of processes in memory). switches from an active to wait state or ii. Non pre-emptive scheduling . terminates.If a new job arrives with certain criteria then the current job will be pre-empted (stopped) for the other. Campbell Copyright @ 2010 Updated Jan 2010 46 . What is the role of the dispatcher? What is the difference between an I/O bound and CPU bound process? How does the long-term scheduler relate to CPU and I/O bound processes? Practice MCQs 1. Research alternate names for the various schedulers.This is the module which gives control of the CPU to the process selected by the short term scheduler. Differentiate between the short term and the long term scheduler.selects from among the jobs in memory which are ready to execute and allocates the CPU to one of them. Differentiate between pre-emptive and non-pre-emptive scheduling. __________ selects processes from the pool and loads them into memory for execution. A. Pre-emptive scheduling . 3. 5. Short term scheduler C.Short Term Scheduler/CPU Scheduler . b) switching to user mode c) jumping to the proper location in the user program to restart the program. CPU scheduling decisions may take place when a job either i. This involves a) switching context. Swapping may be necessary to free up memory. Medium Term Scheduler . At some time later the process can be reintroduced into memory and continued where it left off. CPU scheduler Operating System Concepts Mrs. The long term scheduler executes much less frequently. G. This scheme is called swapping.Some systems introduce an additional. it therefore must be very fast. It removes processes from memory and thus reduces the degree of multiprogramming. Medium term scheduler D. switches from an active to a ready state or iii. The distinction between these two schedulers is the frequency of their execution. switches from wait state to ready or iv. Tutorial Questions 1. Dispatcher . 6.Non-preemptive means that once the CPU is given to a job it cannot be pre-empted (stopped) until it completes its CPU burst. Long term scheduler B. The short term scheduler must select a new process for the CPU quite often.
2. G. Which of the following is true for the high level scheduler? a) It ensures a good mixture of CPU bound and I/O bound jobs b) Its selects which job gets to use the processor next c) It removes jobs from memory d) It uses a processor scheduling algorithm Operating System Concepts Mrs. Campbell Copyright @ 2010 Updated Jan 2010 47 .
CPU scheduling algorithms can be rated on which of the following criteria? a) Pre-emption b) Blocking c) Throughput d) SJF 2. The aim is to keep the CPU as busy as possible. • throughput . The number of processes that are completed per unit of time is called a: A.how busy you keep CPU.time from submission of request until the first response is produced. Tutorial Questions 1. Describe the various scheduling criteria. G.work done/number of jobs completed per unit of time • turnaround time .Scheduling criteria Different scheduling algorithms have different properties and may favour one class of processes over another.how long it takes to execute a job • waiting time – the amount of time that a job spends in the ready queue • response time . turnaround time B. waiting time C. throughput Operating System Concepts Mrs. Campbell Copyright @ 2010 Updated Jan 2010 48 . The criteria for selecting/comparing CPU scheduling algorithms are:• CPU utilization . response time D. Practice MCQs 1.
The operating system has to predict the CPU time that will be used. the jobs/processes are executed in the order in which they enter the system. The average waiting time would therefore be (6+0+3)/3 = 3 Shortest Job First (SJF) In SJF scheduling when the CPU is available the job that is the shortest gets the CPU next. P2. P3. SJF is optimal in that it gives minimum average waiting time for a given set of jobs. This is a non-preemptive algorithm. Then the Gantt chart would be as follows: P2 0 3 P3 6 P1 30 The waiting time for P1 = 6. Example: Process P1 P2 P3 P4 Arrival Time 0 2 4 5 Burst Time 7 4 1 4 The Gantt chart would be as follows: Operating System Concepts Mrs. For example: Process P1 P2 P3 Burst Time 24 3 3 Suppose the processes arrive in the order P1. P1. G. First Come First Served or First In First Out (FCFS/FIFO) For this type of scheduling. P3. for P3 = 3. Then the Gantt chart would be as follows: P1 0 24 P2 27 P3 30 Suppose the processes arrive in the order P2. Campbell Copyright @ 2010 Updated Jan 2010 49 .Scheduling algorithms The purpose of a scheduling algorithm is to select and allocate the CPU to a waiting process. for P2 = 0.
The operating system may increase the priority the longer the job is in the queue.by a person (e. Round robin (RR) In RR scheduling (also called circular queue) each job gets a time quantum or time slice (e. Campbell Copyright @ 2010 Updated Jan 2010 50 .g. 100 msec). G.P1 0 The average waiting time = (0+6+3+7)/4 = 4 7 P3 8 P2 12 P4 16 Priority In priority scheduling the job with the highest priority gets the CPU next. A priority number is associated with each job. system administrator). Priority can be defined:• internally – based on time limits. If there are n jobs in the ready queue and the time quantum is q. • externally . number of open files etc. This process is called aging. memory requirements. If the time quantum is small then overload would be too high. Blocking/starvation occurs when a job is constantly being passed over because of its low priority. Example of RR with time quantum 20 Process P1 P2 P3 P4 Burst Time 53 17 68 24 The Gantt chart would be as follows: P1 0 20 P2 37 P3 57 P4 77 P1 97 P3 117 P4 121 P1 134 P3 154 P3 162 Pre-emptive A pre-emptive algorithm stops a job in middle of the job running if a job that satisfies a criteria comes along.g. No job waits for more than (n-1)q time units. then each job gets 1/n of the CPU time in chunks of at most q time units at once. If the time quantum is large then RR equates to FIFO. Examples of pre-emptive algorithms are: Operating System Concepts Mrs. Usually the smaller number is the highest priority. After this time has elapsed the job is pre-empted and added to the end of the ready queue.
and so might have different scheduling algorithms. What is the purpose of a CPU scheduling algorithm? 2. Given the information in the table below: Job A B C D E Copyright @ 2010 CPU Burst time (sec) 10 1 2 1 5 Priority 3 1 (highest) 3 4 2 Updated Jan 2010 Operating System Concepts Mrs. These two types of jobs have quite different response time requirements. Tutorial Questions 1.• Shortest remaining time first (SRTF) – stops the shortest job if an even shorter job enters the system. if a new job arrives with CPU burst length that is less than the remaining time of the current job then the current job will be pre-empted for the other. generally based on some property of the job. E. In addition. such as memory size or job type. Campbell 51 . A multi-queue scheduling algorithm partitions the ready queue into separate queues. In other words. G. a common division is made between foreground (interactive) jobs and background (batch) jobs. Example: Process P1 P2 P3 P4 Arrival Time 0 2 4 5 Burst Time 7 4 1 4 The Gantt chart would be as follows: P1 0 2 P2 4 P3 5 P2 7 P4 11 P1 16 Average waiting time = (9+1+0+2)/4 = 3 • Pre-emptive priority – stops the highest priority job if a job with a higher priority enters the system.g. foreground jobs may have priority over background jobs. Jobs are permanently assigned to one queue. Multilevel queues Another class of scheduling algorithms has been created for situations in which jobs are easily classified into different groups. Each queue has its own scheduling algorithm.
All of the following affect the degree of multiprogramming except: a) Job scheduler b) Number of partitions c) Medium term scheduler Operating System Concepts Mrs. 3. 4. Priority iv. Round Robin (Time quantum of 2 seconds) b) What is the throughput after 13 seconds for each of the scheduling algorithms? c) What is the turnaround time for each process for each of the scheduling algorithms? d) In this situation. SJF. The problem of starvation can be solved by a) Blocking b) Dispatching c) Multilevel queues d) Aging 2. which algorithm is the most efficient? Why? 4. How does a multi-level feedback queue differ from a multilevel queue? 5. Distinguish between Shortest Job First and Shortest Remaining Time.a) What is the turnaround time and waiting time of each job for FIFO. Campbell Copyright @ 2010 Updated Jan 2010 52 . SJF iii. What advantage is there in having different quantum sizes on different levels of a multi-level queuing system? Practice MCQs 1. Given the following information (Taken from CCCJ Aug 2003 exam) Job Id. FCFS ii. Priority. G. CPU Burst Time (secs) Priority A 6 4 B 2 3 C 9 1 (Highest) D 3 2 a) Use Gantt charts to illustrate the order of execution of these processes using:i. RR (timeslice = 2sec) b) Which algorithm gives the best throughput after 10 secs. A multilevel feedback queue a) Allows jobs to move between queues of different priority b) Have one common queue for batch and interactive jobs c) Assign jobs permanently to a queue d) Allows a job to be in more than one queue at the same time 3.
Round robin scheduling 10. Starvation C. The amount of time that a job gets to use the CPU in round robin scheduling is called a) Circular queue b) Time slice c) Aging d) Priority 5. Which scheduler reduces the degree of multiprogramming? a) Short term b) Medium term c) Intermediate term d) Long term 9. What is the purpose of a processor scheduling algorithm? a) To manage multiple CPUs b) To select and allocate the CPU to a waiting job c) To prevent starvation d) To increase the average waiting time 6. Priority scheduling D. Which scheduler uses a processor scheduling algorithm? a) Short term b) Medium term c) Intermediate term d) Long term 7. Aging B. Which of the following indicates that a low priority process does not get access to an available resource due to the fact that the system is always busy? A. Which of the following indicates that the process that requests the CPU first is allocated first? A. Shortest job first B. First come first served C.d) CPU scheduler 4. G. Fragmentation D. How does a multi-level feedback queuing system carry out aging? a) Swaps jobs out of memory b) Improve the scheduling strategies c) Move jobs to a higher priority queue d) Use longer time slices in RR scheduling 8. Campbell Copyright @ 2010 Updated Jan 2010 53 . Paging Operating System Concepts Mrs.
G. The operating system typically sets aside one or more processors for its exclusive use. SMP is more complex than ASMP. For this reason. Campbell Copyright @ 2010 Updated Jan 2010 54 . a multiprocessing operating system actually does so. Multiprocessing operating systems can be either asymmetric or symmetric. all running at the same time. Multi-processing involves a computer having more than one CPU. Any processor can run any type of thread. SMP systems provide better load-balancing and fault tolerance. A large amount of coordination must take place to keep everything synchronized. Because the operating system threads can run on any processor.Multiple processor scheduling (2 hours) In a multiprocessing system tasks are handled simultaneously. A multiprocessing computer can execute multiple threads simultaneously. A thread is a part of a program that can run independently of other parts. hosts for multiuser interactive sessions. The main difference is in how the processors operate.Lecture 8. Multiple-processor computers are commonly used as high-end server platforms. SMP systems are usually designed and written from the ground up. If the processor that fails is an operating system processor. Operating System Concepts Mrs. A multitasking operating system only appears to execute multiple threads at the same time. the single processor running the operating system can fall behind the processors running user applications. and single-user systems for running resource intensive desktop applications. independent executable components of applications) of execution. alleviating the need for data sharing. Symmetric Multiprocessing Symmetric multi-processing (SMP) is used to get higher levels of performance. The processors communicate with each other through shared memory. the whole computer can go down. As a result. Multithreading operating systems allow programmers to design programs that have threaded parts that can run concurrently. Asymmetric multiprocessing Asymmetric multi-processing (ASMP) is where only one processor accesses the system data structures. All processors are allowed to run a mixture of application and operating system code. Multitasking is an operating-system technique for sharing a single processor among multiple threads (small. the chance of hitting a CPU bottleneck is greatly reduced. one thread for each processor in the computer. The remainder of the processors run user applications. This forces the applications to wait while the operating system catches up. which reduces the overall throughput of the system. A processor failure reduces the computing capacity of the system.
multitasking B. 3. Multitasking D. all Pentium 4) – There is a separate queue for each processor or they all use a common queue. They are tightly integrated so that they can work together on a job by sharing memory. Campbell Copyright @ 2010 Updated Jan 2010 55 . In parallel processing. • Heterogenous system (different processors – e. Practice MCQs 1. ________________ is the ability of an operating system to execute different parts of a program at the same time. 3 Pentium II. Multiprocessing C. Multitasking Operating System Concepts Mrs. Multiprogramming B. 1 AMD. A ____________ operating system can support two or more CPUs running programs at the same time.Homogenous and Heterogenous systems Multiprocessing can also be categorized as being homogenous or heterogenous. which is the most sophisticated and fastest type of multiprocessing. G. Multiprogramming 2. multiuser D. multiprocessing C. Parallel processor C. Multithreading D. Coprocessor B. 2. How does multi-programming differ from parallel processing? What is a thread? What is the difference between user threads and kernel threads? What is the dining philosopher's problem? What is a semaphore? Describe busy waiting and the critical section problem? Differentiate between symmetric and asymmetric multiprocessing. Jobs are typed by their structure and must be run on a particular processor. 2 Motorola 68030) Each processor has its own queue and its own scheduling algorithm. the multiple processors involved are full-fledged general purpose CPUs. A. Tutorial Questions 1. multiprogramming 3.g. 4. 5. 6. A. • Homogenous system (all processors identical – e.g. ___________ method uses multiple processors simultaneously to execute a program. A.
symmetric multiprocessing C. multiprogramming Operating System Concepts Mrs. asymmetric multiprocessing B.4. G. multiprocessing D. Campbell Copyright @ 2010 Updated Jan 2010 56 . When one processor accesses the system data structure and therefore reduces data sharing this is known as: A.
If we must keep several processes in memory. Code sharing If the code of a program is invariant (not altered by the program). Multiple Segments The process is logically composed of a number of segments: code. It may be required to have these segments in physically disjoint memory areas. stack and data segments must appear to be logically contiguous. Everything cannot hold in this limited space at any one time. 2. Transparency Memory allocation should be invisible to the process. It should not matter where in memory the process has been placed. There are four requirements of a memory management system:1. and arranges for the appropriate images to be present in main memory when they are required. 2. and if such a program is simultaneously part of two or more process images it may be desirable to keep a single physical copy of the code segment. If the process had to be put on the disk and then reloaded into a different memory location. Campbell Copyright @ 2010 Updated Jan 2010 57 . stack and system data. Memory mapping . Research the MMU or PMMU. 3. which appears logically in all the appropriate process images. G. If more than one process is in memory at any one time there is an additional need to enforce mutual protection between them.Lecture 9 .the memory management software presents an interface that simulates an apparently infinite memory. it will be sharing the memory with the kernel/monitor. Protection Even if only one process is in memory at a time. It is therefore necessary to have another layer of software in the operating system that stores process images on disk. and it is imperative that a malfunction of the process should not overwrite kernel code or data. 4.Memory Management (1 hour) Introduction Multi-programming causes processes to have to share memory. data. though the code. Each machine has a certain amount of memory. Operating System Concepts Mrs. it still should not matter. Find out the different memory requirements of different modern operating systems. This is done in such a way that the process is not aware of the movement between disk and main memory .Distinguish between the logical address seen by the executing program and the physical address of the actual memory. we must share memory. Tutorial Questions 1.
Practice MCQs 1. All of the following are requirements for a memory management system except: a) Protection b) Transitivity c) Multiple Segments d) Code Sharing Operating System Concepts Mrs. Campbell Copyright @ 2010 Updated Jan 2010 58 . G.
non-volatile disk storage. while the access time increases and the amount of storage at each level increases. Discuss the different secondary (auxiliary) storage device. Operating System Concepts Mrs. with a small amount of very fast. 5. When a memory access is made. Research how to increase the RAM in a computer. they can be fetched directly from the cache without having to go to the slower speed main memory. 4. plus its neighbours are copied to the cache. expensive. The higher levels are expensive. Describe the different types of cache. As we move down the hierarchy the cost per bit decreases. volatile cache memory. the contents of the accessed location. Research the cost of different types and sizes of RAM as well as the cost of different types and sizes of hard disks. 2. Campbell Copyright @ 2010 Updated Jan 2010 59 . medium priced volatile main memory (RAM) and a large amount of slow. The part of the operating system that manages this hierarchy is called the memory manager. If another reference is made to this location.Memory hierarchy Most computers have a memory hierarchy (storage hierarchy). Describe the different types of RAM. G. Compare and contrast them. but very fast. cheap. It is the job of the operating system to co-ordinate how these memories are used. which can be organized in a hierarchy. 3. some medium speed. There is a wide variety of storage in a computer system. Make sure you find out some of the precautions that you need to take. MEMORY HIERARCHY Tutorial Questions 1.
Cache D. cache 3. Cache B. Electronic Disk C. register. Which of the following is the fastest and MOST expensive type of storage? A. RAM. a) Hard disk. cache b) Cache. What are the characteristics of memory at the top of the hierarchy? a) Cheaper and larger in capacity b) Cheaper and smaller in capacity c) Faster and larger in capacity d) Faster and smaller in capacity 4. RAM. Main memory D. G. Magnetic Disk Operating System Concepts Mrs. Which of the following storage device is the slowest? A. register. Memory that is at the top of the hierarchy is a) Slower and more expensive b) Non-volatile and slower c) Non-volatile and more expensive d) Faster and more expensive 2. Registers C.Practice MCQs 1. hard disk c) Register. Magnetic Disk B. hard disk d) Hard disk. RAM. cache. register. Campbell Copyright @ 2010 Updated Jan 2010 60 . What are the characteristics of memory at the bottom of the hierarchy? a) Cheaper and larger in capacity b) Cheaper and smaller in capacity c) Faster and larger in capacity d) Faster and smaller in capacity 5. RAM. Main Memory 6. Select the correct ordering of memory in the storage hierarchy.
G. is located external to the CPU and holds the instructions and the data that the program requires. It is a special. RAM is much slower than registers and there is a lot more RAM than registers. To do this there needs to be a way to determine the range of legal addresses that the program may access.Basic memory hardware – base register. and several specialized registers including a base register. the compiler is responsible for translating high-level operations into low-level operations that access registers. Operating System Concepts Mrs. flags register. these include a program counter. Usually. each CPU instruction can manipulate 32 bits of data.Lecture 10 . The base register holds the smallest legal physical memory address. data has to be loaded into a CPU register from memory before the CPU can process it. Effective addresses are calculated by adding the contents of the base or segment register to the rest of the effective address computation. the movement of data in and out of registers is completely transparent to users. Intel chips have 6 general purpose registers. Base registers or segment registers are used to segment memory. whereas the limit register specifies the size of the range. or RAM. limit register (1 hour) What is a register? A register (or memory register) temporarily stores one computer word in the main internal memory of a digital computer. program counter. CPU instructions operate on these values directly. memory management software ensures that memory is shared among different programs. The operating system needs to ensure that each program has its own memory space. Campbell Copyright @ 2010 Updated Jan 2010 61 . stack register. There are generally only a few registers available on a processer. In high-level languages. The number of registers that a CPU has and the size of each (number of bits) help determine the power and speed of a CPU. Types of registers As previously stated. registers are storage locations internal to the processor. high-speed storage area within the CPU. This can be done by using two registers: a base register and a limit register. In other words. In general. and even to programmers. if the base register holds 300020 and the limit register holds 120800. For example. and flags. For example a 32-bit CPU is one in which each register is 32 bits wide. Memory. There are also registers that are reserved for certain tasks. Therefore. then the program can legally access all addresses from 300020 to 420820 (inclusive). and some addressing registers. stack. Only assembly language programs can manipulate registers. In other words it holds the data that the CPU is currently working on.
Operating System Concepts Mrs. A base-bound register is associated with each segment of data or code and defines the position in physical memory of word zero for that segment. Discuss the other types of registers. Campbell Copyright @ 2010 Updated Jan 2010 62 . the so-called base. in which case it is a bounds register).A bounds register is a device which stores the upper and lower bounds on addresses in the memory of a given computer program. Find out the processors that have 32-bit registers. G. the so-called bound or limit (or alternatively the physical memory address of the next word after the end of the segment. and the number of words available to that segment. A base-bound register (base-limit register) is hardware used for virtual-memory allocation. 2. Tutorial Questions 1.
Logical vs.Lecture 11 . The fence register is a type of bounds register. but the first address beyond the fence. 2. Monitor < Fence address User Memory We can protect the monitor code and data from changes (accidental or malicious) by using a fence address. The logical address is also known as the virtual address. Differentiate between a logical and a physical address. logical address)? See if you can come up with a formula. The fence address can be a) built into the hardware. Although the address space of the computer starts at 00000. This is known as relocation mapping or memory mapping. while a logical address space is an address generated by the CPU. G. Campbell Copyright @ 2010 Updated Jan 2010 63 . This arrangement may affect the addresses that the user program uses. It is possible to place the monitor into either low memory or high memory. Physical address space (1 hour) Memory is divided into two sections. one for the user and one for the resident monitor. Segment Base Length 0 219 600 1 2300 14 2 90 1000 3 1327 586 4 1952 196 What are the physical addresses for the following logical addresses (segment. The physical address space is therefore an address as seen by the memory unit. Consider the segment table. The user never sees the real physical address but only the logical address. the first address of the user program is not 00000. b) placed in a fence register. The fence address is added to the address generated by the user process at the time that it is sent to memory. Tutorial Questions 1. The logical address space is used by user programs. User programs are run in their own area of memory. Operating System Concepts Mrs.
430 2. 112 Practice MCQs 1. 10 1. G.a) b) c) d) e) f) 1. Adding the fence address to a user program in RAM is a) Relocation mapping b) Code sharing c) Blocking d) Compaction Operating System Concepts Mrs. 500 3. Campbell Copyright @ 2010 Updated Jan 2010 64 . 400 4. 11 0.
spending all its resources moving pages to and from memory. Describe the concept of swapping. Swapping therefore attempts to put only currently running processes in memory. the kernel begins to swap memory pages to and from the disk. The advantage of swapping is that more processes can use memory more efficiently. over and over again: • • • Pages from a process are swapped The process becomes runnable and attempts to access a swapped page The page is faulted back into memory (most likely forcing some other processes' pages to be swapped out) A short time later. It occurs when a process needs to be in memory to execute and can be swapped to a backing store (temporarily) then brought back into memory for continued execution. ___________ consists of bringing in each process in its entirety.Lecture 12 – Swapping (1 hour) When a process running on a computer attempts to allocate more memory than the system has available. It is not necessary to keep inactive processes in memory. Why would swapping be necessary? 3. Thrashing is extremely detrimental to system performance. it is known as thrashing and is indicative of insufficient RAM for the present workload. it is possible to experience too much swapping. In extreme cases. The disadvantage however is the time taken to perform swapping (overhead). Operating System Concepts Mrs. It should also be noted that not all processes can be swapped so care must be taken. Practice MCQs 1. Although paging is the primary mechanism for virtual memory. This is done in order to free up sufficient physical memory to meet the RAM allocation requirements of the requestor. Swapping (writing modified pages out to the system swap space) is a normal part of a system's operation. Campbell Copyright @ 2010 Updated Jan 2010 65 . Tutorial Questions 1. Swapping on a virtual memory computer is therefore the transfer of program segments (pages) into and out of memory. G. running it for a while. The reason to be wary of excessive swapping is that the following situation can easily occur. 2. the page is swapped out again • If this sequence of events is widespread. Discus the concept of the swap file in Windows. excessive paging is not desirable. as the CPU and I/O loads that can be generated in such a situation can quickly outweigh the load imposed by a system's real work. Swapping maximizes available memory. the system may actually do no useful work.
Swapping D. G. Campbell Copyright @ 2010 Updated Jan 2010 66 .then putting it back on the disk. Paging C. Scheduling B. Fragmentation Operating System Concepts Mrs. A.
indexed. Contiguous allocation This requires each file to occupy a set of contiguous addresses on the disk. then the file cannot be extended/made larger.Lecture 13 . Contiguous allocation of a file is defined by the disk address of the first block and its length. The blocks chosen for the file are chosen by one of three memory allocation strategies or algorithms: first fit. we must search for n free contiguous blocks. Non-contiguous allocation a) Linked allocation Each file is a linked list of disk blocks. Accessing a file. many files will be stored on the same disk. worst fit. since all blocks are linked together. Compaction . simply read blocks by following the pointers from block to block. If the file to be created is n blocks long. we can immediately access block b + n. best fit. The algorithms suffer from fragmentation. Each block contains a pointer to the next block. The main problem is how to allocate space to these files so that disk space is effectively utilized and files can be quickly accessed. To read a file. External fragmentation exists when enough total disk space exists to satisfy a request but it is not contiguous.Contiguous vs non contiguous memory allocation (4 hours) In almost every case. If too little space is allocated. Another problem of contiguous allocation is to know how much free space (holes) to give to a file.This re-allocates the files to allow all free space to be one contiguous space. the disk blocks may be scattered anywhere on the disk. Any free block can be used to satisfy a request. There is no need to declare the size of a file when it Operating System Concepts Mrs. This solves the fragmentation problem. which has been contiguously allocated is fairly easy. Overestimating the file size also wastes space. For direct access to block n of a file which starts at block b. For sequential access. Each method has its advantages and disadvantages. Free disk space gets broken into little pieces as files are allocated and deleted. Campbell Copyright @ 2010 Updated Jan 2010 67 . Disk addresses define a linear ordering on the disk. Thus both sequential and direct access can be supported by contiguous allocation. The difficulty with contiguous allocation is finding space for a new file. the file system remembers the disk address of the last block and when necessary reads the next block. The directory contains a pointer to the first (and last) blocks of the file. There is no external fragmentation with linked allocation. G. linked. Three major methods of allocating disk space are in use: contiguous.
The directory contains the address of the index block. It is never necessary to compact disk space. Some operating systems support direct access files by using contiguous allocation and sequential access files by using linked allocation. Another disadvantage is the space required for the pointers. To read the nth block. added at the end. A file currently consists of 100 blocks. 4. link and indexed allocation methods if one block is: added at the start. b) Indexed allocation Each file has its own index block. The major problem with linked allocation is that it can only be used effectively for sequential access files. a programmer. Campbell Copyright @ 2010 Updated Jan 2010 68 . Since the files are linked together by pointers scattered all over the disk. G. The pointers are however not scattered all over the disk. Each access to a pointer requires a disk read. removed from the start. we must start at the beginning of that file and follow the pointers until we get to the nth block. Index allocation supports direct access without suffering from external fragmentation. removed from the middle. Explain three (3) storage allocation methods.is created. 3. removed from the end? Operating System Concepts Mrs. Tutorial Questions 1. The pointer overhead of the index block is generally worse that the pointer overhead of linked allocation. added in the middle. To find the nth block of a file. which is an array of disk block addresses. If the index block is damaged then the entire file is lost. In order to conserve on space. Brown needs fast and easy access to the files using both sequential and direct access methods. How many disk I/O operations are involved with contiguous. How would you represent each with a diagram? 2. It also does not suffer from wasted space. Hence we cannot support a direct access capability for linked allocation files. 5. A file can continue to grow as long as there are free blocks. Discuss the criteria that should be used in deciding which storage allocation strategy should be used for a particular file. Brown use? Give reasons for your choice. we use the pointer in the nth index block entry to find and read the desired block. Another problem is reliability. Mr. Any free block anywhere on the disk may satisfy a request for more space. consider what would happen if a pointer is lost or damaged. John Brown. needs to work with certain files. Which storage allocation method would you recommend that Mr. List the advantages and disadvantages of each storage allocation method. The nth entry in the index block points to the nth block of the file. the files should use memory space in an optimal manner. The sizes of the files are known from the start and will not grow in size.
Practice MCQs 1. Which of the following is true about linked allocation? a) It can be used only for sequential files b) It requires compaction c) It is very reliable d) There is external fragmentation 2. A disadvantage of contiguous allocation is a) It allows access to sequential files only b) It allows any free block to be used c) It is unreliable d) It suffers from fragmentation 3. Which storage allocation method requires compaction utilities? a) Contiguous b) Linked c) Indexed d) All of the above 4. Which storage allocation method requires de-fragmentation utilities? a) Contiguous b) Indexed c) Linked d) Listed 5. Which of the following is TRUE for a contiguous storage allocation scheme? a) The directory points to the first and last block b) The access method is limited to sequential only c) The directory points to the first block d) There is no need for compaction 6. All of the following are TRUE for indexed storage allocation EXCEPT: a) The directory points to the index block b) Only sequential access is allowed c) It does not suffer from fragmentation d) All of the pointers are in one block 7. Which of the file allocation methods is not randomly accessed? A. Contiguous allocation B. Linked Allocation C. Indexed allocation D. Addressed allocation
Operating System Concepts Mrs. G. Campbell Copyright @ 2010
Updated Jan 2010
Memory allocation strategies – first fit, best-fit, worst-fit The memory allocation strategies or algorithms are used to find space for a new file in contiguous memory allocation. The free contiguous blocks for placement of the file are chosen by one of three memory allocation strategies. The strategies are as follows: • first fit - allocate the first set of blocks that is big enough. • best fit - allocate the smallest set of blocks that is big enough. We must search the entire list, unless the list is ordered by size. • worst fit - allocates the largest set of blocks. Tutorial Questions 1. Given a computer with 33 blocks of memory with block sizes 512KB and a file size of 2519KB. Place the file in memory using contiguous allocation – a) first fit, b) best fit and c) worst fit. Please note that blocks 1-4, 7-14, 16-24 and 28-33 are free. 2. Given a computer with 14 blocks of memory with blocks 1-3, 5-6, 9-12 free. a) If a 2 block file is to be saved in blocks 5-6, which storage allocation algorithm was used? b) If a 2 block file is to be saved in blocks 1-2, which storage allocation algorithm was used?
Practice MCQs
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Figure 1 1. Using Figure 1. If a two block file is to be placed in blocks 7 and 8, then the allocation algorithm used is a) First fit b) Best fit c) Worst fit d) Just fit 2. Using Figure 1. If a two block file is to be placed in blocks 13 and 14, then the allocation algorithm used is
Operating System Concepts Mrs. G. Campbell Copyright @ 2010 Updated Jan 2010
a) b) c) d)
First fit Best fit Worst fit Just fit
3. Which type of contiguous storage allocation uses the smallest set of blocks that is large enough? a) Best fit b) Least fit c) Smallest fit d) Worst fit 4. Given memory that has 10 blocks with blocks 3 and 8 in use. Where would you place a 2block file using the worst-fit algorithm? a) Blocks 1 and 2 b) Blocks 4 and 5 c) Blocks 9 and 10 d) All of the above
Operating System Concepts Mrs. G. Campbell Copyright @ 2010
Updated Jan 2010
However this is sometimes not enough to reclaim significant amount of memory • Compaction (garbage collection) – this is where memory is rearranged into a single contiguous block of occupied space and a single contiguous block of free space. Bounds registers keep track of the upper and lower boundaries of each partition. the partition sizes are set and do not change. Partition sizes vary dynamically. External fragmentation can be dealt with in the following ways: • Coalescing – this is where adjacent free blocks are merged into one large block. Partitioned memory Types of partitioning In fixed partition multi-programming. G. external fragmentation (see next section) can occur when processes are removed from memory. This however comes with a lot of overhead. The operating system does this by keeping a table indicating which parts of the memory are available and which are occupied by the different programs. This leaves holes too small for new processes and eventually no holes will be large enough for new processes. Another drawback is that there may be a process that does not fit in any partition. This method suffers from internal fragmentation (see next section). Internal fragmentation is not possible as partitions are the exact size. The degree of multiprogramming is therefore dependent on the number of partitions. In variable partition multi-programming. When a region is free. Operating System Concepts Mrs.Lecture 14 – Partitions and Fragmentation (1 hour) Partitions Memory is divided into a number of regions or partitions. These are also called base and limit registers (or low and high). a program is selected from the job queue and loaded into the free region. thereby protecting each partition from interference by other jobs. Jobs are scheduled to go to the different partitions based on the size. partition sizes vary depending of the size of the jobs being run. Each region may have one program to be executed. Campbell Copyright @ 2010 Updated Jan 2010 72 . No space is wasted initially. However.
Campbell Copyright @ 2010 Updated Jan 2010 73 .Example of fixed partition multi-programming with absolute translation and loading Example of fixed partition multi-programming with relocatable translation and loading Operating System Concepts Mrs. G.
Multiple and fixed B. Campbell Copyright @ 2010 Updated Jan 2010 74 . Single and multiple D.Example of variable partition multi-programming Tutorial Questions 1. What are the names of the two (2) types of partitions? A. What are they? Practice MCQs 1. G. Fixed and variable C. The degree of multi-programming is dependent on a number of things. Single and variable Operating System Concepts Mrs.
Fragmentation – internal. Campbell Copyright @ 2010 Updated Jan 2010 75 . 2. Internal fragmentation – this occurs when a job is in a region of memory that is larger than the job needs. Compaction is the a) Compression of sizes of files b) Rearrangement of the location of files c) Deletion of files d) Fragmentation of files Operating System Concepts Mrs. Practice MCQs 1. Use diagrams to depict both internal and external fragmentation. Differentiate between internal and external fragmentation. The diagram below shows a waiting job that cannot fit into memory even though space is available free used free used Memory Example of external fragmentation Waiting job Compaction – this is where the operating system shuffles the memory contents to place all free memory together in one large block. G. In the diagram below only part of a memory partition is being used by the job but the free space cannot be used by any other job free Used < Wasted space Memory partition Example of internal fragmentation External fragmentation – this occurs when a region of memory is unused and available but is still too small for any waiting job. Tutorial Questions 1. external Fragmentation is wasted memory space (available but cannot be used). the extra space wasted.
What is virtual memory? 2. A. Buffer Virtual Address Space The virtual address (VA) space of a program refers to how much memory the program would need if it needed all the memory at once. segmentation.Introduction to Virtual Memory (1 hour) We have just looked at memory management strategies. However they all require the entire process to be in memory before the process can execute. Virtual means that this is the total number of uniquelyaddressable memory locations required by the program. Why is virtual memory necessary? 3. swapping are necessary because the entire logical address space of a process must be in physical memory before the process can execute. Practice MCQs 1. G. E. But if you look at a program it shows in many cases that the entire program is not needed. This limits the size of a program to the size of physical memory. usually the hard disk. Register C. Tutorial Questions 1. and not the amount of physical memory that must be dedicated to the program at any given time. These had the goal of keeping many processes in memory simultaneously to allow multiprogramming. Memory management procedures such as paging. List the various virtual memory strategies. partitioning. Virtual memory D. Virtual memory/storage is the use of secondary storage (disk) to simulate the presence of primary storage. 2) arrays lists. Virtual memory is the separation of user logical memory from physical memory.Lecture 15 . Even where the entire program is needed it may not need all of it at the same time. 1) code to handle errors. It allows the execution of processes that may not be completely in memory. Virtual memory allows the execution of processes that may not be completely in memory. Cache B. Operating System Concepts Mrs. The main advantage is that user programs can be larger than physical memory. _____________ is a portion of a storage medium. tables are often allocated more memory than they need.g. which functions as additional memory. Campbell Copyright @ 2010 Updated Jan 2010 76 .
offset> where the page is determined by dividing each process into fixed size pages.(page size . VA has two components: the page number and the address in page (or offset or displacement) An example of Virtual Address to Physical Address Mapping Operating System Concepts Mrs. In pure paging systems the entire VA space of a process must reside in physical memory during execution.1).A virtual address is represented as <page. Memory is divided into fixed size blocks (or page frames) and accommodates a process' pages. but pages are not kept in contiguous blocks. The physical address (PA) then is (block_number * page_size + offset). the offset is a number in the range 0 . Campbell Copyright @ 2010 Updated Jan 2010 77 . G. VA is determined from the compiled address.
Some of the pages are stored on disk and brought into memory when required. containing only this one program. The first page is in memory location 1. For example. Programs or processes are divided into fixed size pieces called pages and main memory is divided into fixed size partitions called page frames or blocks. sometimes called a memory management unit. If the page tables indicate that the virtual memory page is not currently in real memory. the program is scattered throughout physical memory. Paging is to solve the problem of fragmentation. the next in memory location 3 and the last is in memory location 7. a file is made up of 4 pages. (E. In pure paging the total program is kept in memory as sets of (non-contiguous) pages. Novell Netware . The page table maps logical memory to physical memory. a CPU fetches an instruction located at a particular virtual address. This is done by a hardware component. which looks up the real address (from the page table) corresponding to a virtual address and passes the real address to the parts of the CPU which execute instructions. in the following diagram.page size is 4K blocks by default). the virtual address must be translated to the corresponding physical address. which also holds other programs. They are therefore scattered in memory. the hardware raises a page fault exception (special internal signal) which invokes the paging supervisor component of the operating system. It does this by mapping contiguous logical space on to small disjoint areas of physical memory. The basic idea of paging is to divide the memory into page frames of fixed size (typically between 512 and 2048 bytes). The page table organizes the pages. A Page table (set of dedicated registers) has a bit indicating whether page is resident (gives memory address) or non-resident (gives disk address). the other is in memory location 4. Virtual memory is used to increase the degree of multiprogramming. This is due to the fact that you have more space in memory because all the pages would not be there to take up space. or fetches data from a specific virtual address or stores data to a particular virtual address. therefore in logical memory the pages seem to be placed one after the other in the proper sequence. In reality.Pure paging (2 hours) Paging is the most common virtual memory system. The user program believes that memory is one contiguous space. Campbell Copyright @ 2010 Updated Jan 2010 78 .Lecture 16 . Page 0 Page 1 Page 2 Page 3 Logical Memory 0 1 2 3 1 4 3 7 Page Table 0 1 2 3 4 5 6 7 Page 0 Page 2 Page 1 Page 3 Physical Memory Dynamic address translation If during the execution of an instruction.g. G. Operating System Concepts Mrs.
3. Explain the concept of a page table. G. 2. 4.Paging solves the problem of external fragmentation. Differentiate between a page and a page frame. Describe paging. Discuss PTBR and TLB. Operating System Concepts Mrs. Campbell Copyright @ 2010 Updated Jan 2010 79 . Advantages: • Efficient memory usage • Simple partition management due to is contiguous loading and fixed partition size • No compaction necessary • Easy to share pages Disadvantages: • Job Size <= Memory Size • Internal fragmentation (half the page size on the average) • Need special hardware for address translation • Some main memory space used for page map tables (PMT's) • Address translation lengthens memory cycle times Tutorial Questions 1.
Locked pages cannot be replaced. Therefore the operating system needs to estimate when next it will be used. Most frequently used (MFU) The O/S replaces the page with the highest count. This has the lowest page fault rate. Optimal replacement The O/S replaces the page that will not be used for the longest period of time. LFU. G. A page fault occurs when a required page is not currently in memory and has to be loaded in.Page replacement (3 hours) Page replacement algorithms decide which page is overwritten when a new page needs to be brought into memory.Lecture 17 . Campbell Copyright @ 2010 Updated Jan 2010 80 . The allocation algorithms are as follows:• split them equally – memory is equally divided up among the processes Operating System Concepts Mrs. This does not suffer from the anomaly. In other words. the page that has already been used the most. Least frequently used (LFU) The O/S replaces the page with the smallest count. Optimal replacement. Allocation algorithms therefore are used to decide the number of page frames that a particular process receives. the page that has been used the least so far. which may be difficult.uses number of reference bits to know if page was recently used. MFU. This method never suffers from the anomaly. A version of this algorithm is LRU approximation . LRU. FIFO The O/S chooses the oldest page. Allocation algorithms When several processes are running in memory it is possible that the different processes could be allocated different amounts of memory. In general you want the one with the lowest page fault rate. This algorithm suffers from Belady's anomaly which is where the page fault rate may increase as the number of page frames increase. Least recently used (LRU) The O/S replaces the page which has not been used for the longest period of time. In other words. This is hardware and overhead intensive. The algorithms are FIFO. NB.
What page would be replaced next using MFU. Given the following table of jobs to be run. FIFO. 5. 4. 7. Practice MCQs 1. 8. Counting based page replacement D. 5. 9. Least recently used page replacement C. G. 3. First-in-first-out algorithm 2. 9. 8. Least regularly used C. 5. 9. how many blocks would the operating system give to each job using each allocation algorithm? Job A B C D Memory Requirement (MB) 10 20 5 10 Priority 2 1 (highest) 3 4 4. ___________ algorithm associates each page with the time when the page was brought into memory. 2. Campbell Copyright @ 2010 Updated Jan 2010 81 . Research the second-chance and any other page replacement algorithms. 3. Optimal page replacement B. 8. 2. What page would be replaced next using MFU. LRU stands for: A. 3. 8. 2. What is a page fault? 5. LFU. 2. Memory on John's computer is made up of 10 blocks each 1MB. 4. Last recently used Operating System Concepts Mrs. 8. A. LRU? 3. Least recently used B. 9. 4. If the following pages were used in the following order: 7. Likely regularly used D. 6. 5. If the following pages were used in the following order: 8. 2. FIFO. 4. 1. LFU. 3. 3.• proportional allocation – each process is allocated memory based on the amount of memory that each process will use • by priority of process – higher priority processes will be allocated more memory and lower priority processes will be allocated less memory Tutorial Questions 1. LRU? 2.
since protection fault can be used to get page fault. G. as opposed to loading all pages immediately: • • Only loads pages that are demanded by the executing process. Advantages Demand paging. Easy to share pages Can run a program larger than physical memory • • • • Disadvantages • Individual programs face extra latency when they access a page for the first time. Repaging is an attempt to bring in all of the pages that will be needed at one time. the pager guesses which pages will be used prior to the process being swapped out again. Demand paging is the characteristic of a virtual memory system which retrieves only that part of a user's program which is required during execution. Therefore. Locked pages cannot be replaced until a process is complete. not only is unnecessary page load during swapping avoided but we also try to preempt which pages will be needed and avoid loading pages during execution. When a process is to be swapped into main memory for processing.Demand Paging (2 hours) The operating system may try to predict the pages that will be needed next and load them into memory so that they are ready when needed. where all memory for a process is swapped from secondary storage to main memory during the process startup. This process avoids loading pages that are unlikely to be used and focuses on pages needed during the current process execution period. As there is more space in main memory. So demand paging may have lower performance than anticipatory paging algorithms such as prepaging. Campbell Copyright @ 2010 82 . This is known as demand paging. Less loading latency occurs at program startup. as less information is accessed from secondary storage and less information is brought into main memory. The pager will only load these pages into memory. more processes can be loaded reducing context switching time which utilizes large amounts of resources. To do this a lock bit is associated with each page. or you can load in the page when required. Updated Jan 2010 Operating System Concepts Mrs.Lecture 18 . When demand paging is used it is sometimes necessary to allow some of its pages to be locked in memory. Compare demand paging to pure swapping. Does not need extra hardware support than what paging needs.
How does pure paging differ from demand paging? 2. A page that cannot be replaced until the job has been completed is a a) Demand page b) Locked page c) Priority page d) Virtual page 2.• Programs running on low-cost. Thrashing can cause severe performance problems. High paging activity thrashing can occur if the number of pages/frames are too small. The generation of needless traffic to and from disk is known as thrashing. G. Research methods used by operating systems to reduce thrashing. Practice MCQs 1. Memory management with page replacement algorithms becomes slightly more complex. Possible security risks. low-power embedded systems may not have a memory management unit that supports page replacement. Predicting the page that will be needed next and loading it into RAM is a) Page replacement b) Multiprogramming c) Demand paging d) Optimal replacement 3. Internal fragmentation Needs special address translation hardware • • • • Thrashing Thrashing occurs if the currently active pages are habitually removed from memory unto disk. A process is thrashing if it is spending more time paging than executing. Campbell Copyright @ 2010 Updated Jan 2010 83 . The problem of the page fault rate increasing as the number of pages increase is called Operating System Concepts Mrs. including vulnerability to timing attacks. Continuously removing the same page from RAM is a) Thrashing b) Most frequently used c) Page table d) Segmenting 4. Tutorial Questions 1.
Campbell Copyright @ 2010 Updated Jan 2010 84 . Spooling D. A.a) b) c) d) Newton's Law Virtual Storage Belady's Anomaly Starvation 5. 3 670 bytes D. G. 8. Frame allocation D. How much space would be wasted if a file of size 36 KB were to be saved? a) 0KB b) 4KB c) 28KB d) 288KB 7. 26 C. 4 096 bytes C. 3 648 bytes 10. How much is the internal fragmentation? A. 25 9. Buffering C. _____________ indicates that the operating system spends much of its time paging instead of executing application software. Belady's anomaly C. What is a page fault? a) There is something wrong with the page b) The page size needs to be increased c) The required page is not currently in memory d) The page has encountered fragmentation 6. 23 D. 40 B. Paging The following refers to questions 8 & 9. Given a paging scheme in which pages are 8KB. If a page size is 4KB and a process is 97856 bytes. Page allocation Operating System Concepts Mrs. 4 000 bytes B. When the page fault increases as the number of allocated frames increases is known as: A. How many pages does it need? A. Paging B. Thrashing B.
The hardware also compares the offset d with the length l to determine if the address is valid. segments can be of arbitrary length to suit the situation. Given a logical address (segment. This virtual memory strategy provides a 2 dimensional addressing system. offset) = (s. A CPU register holds the starting address of the segment table. This method is similar to paging but unlike pages.Lecture 19 – Segmentation (1 hour) Some systems do not use paging to implement virtual memory. Campbell Copyright @ 2010 Updated Jan 2010 85 . A segment table is maintained for each process. Example of Segmentation Operating System Concepts Mrs. The physical address is obtained by adding d to k. which are of fixed size. A virtual address consists of a segment number and a displacement or an offset within the segment. The segment table contains the starting physical address of the segment as well as the size of the segment for protection. they use segmentation. Instead. G. we access the sth entry in the segment table to get base physical address k and the length l of that segment. so that an application's virtual address space is divided into variable-length segments.d).
4. Discuss the ways in which this strategy is implemented. each table entry has: – base – contains the starting physical address where the segments reside in memory. Discuss the strategy that allows Jane to do this. • Segment table – maps two-dimensional physical addresses. so segmentation can be demand segmentation. Why are paging and segmentation sometimes combined into one scheme? 6. 7. ii. 2. Campbell Copyright @ 2010 Updated Jan 2010 86 . G. • Segment-table base register (STBR) points to the segment table's location in memory. Describe the use of overlays as a virtual storage strategy. How does segmentation differ from paging? Just as paging can be demand paging. segment-number s is legal if s < STLR. Tutorial Questions 1. What problems could arise with segment replacement that would not occur with page replacement? 5. – limit – specifies the length of the segment.Address Translation in Segmentation Based on the diagrams above: • The Logical address consists of a two items: <segment-number. Use a diagram to explain the concept of a segment table. Jane is able to create a program that is larger than her computer's RAM i. • Segment-table length register (STLR) indicates number of segments used by a program. Operating System Concepts Mrs. Segmentation has no internal fragmentation but has external fragmentation if a segment is too large to fit into a slot. Describe a reasonable segment replacement algorithm. 3. offset>. We need a segment replacement algorithm (just like a page replacement algorithm). List the names of operating systems that use segmentation.
what is the physical address for the logical address 12? a) 0012 b) 5500 c) 5511 d) 5512 Operating System Concepts Mrs. If a paging scheme has pages of 4KB and segmentation scheme has a maximum segment size of 32KB. Campbell Copyright @ 2010 Updated Jan 2010 87 . Given a segment that starts at memory area 5500.8. How does paging differ from segmentation? a) In paging blocks are of a fixed size whereas in segmentation blocks vary in size b) In paging blocks vary in size whereas in segmentation blocks are of a fixed size c) Paging blocks are contained within segmented blocks in memory d) There is no difference between them 2. G. b) segmentation? Practice MCQs 1. How much space is wasted if a 6KB file is saved in a) paging.
RAM is volatile which means that information is lost if the power is switched off. Discuss the different auxiliary storage media. size and speed. RAM and Optical disks RAM . Campbell Copyright @ 2010 Updated Jan 2010 88 . Blocks I/O devices can be roughly divided into two categories: block devices and character devices. memory mapping) Tutorial Questions 1. Another approach was to have separate heads on each side of the platter.Auxiliary storage management (1 hour) Introduction Disks were originally designed for file storage so the primary design criteria were cost. To improve the performance of a disk. so that the location is known. The physical address of each block is mapped to a logical address in RAM. numbered from 0.another name for main storage.A physical unit of transfer between tape (secondary) and internal (primary) storage. Engineers are always trying to provide additional storage capacity. some disks (called fixed head disks) have a read/write head for each track.Lecture 20 . Operating System Concepts Mrs. The head therefore did not have to move to a specific track. 2.random access memory . The kernel of the operating system gets loaded here when you boot up the machine. One approach was to improve recording density (reflected by the number of tracks per inch and hence the total number of tracks). Each location has a 0 or 1. What is auxiliary storage? How does it differ from primary storage? 2. The essential property of a block device is that it is possible to read or write each block independently of all the other ones. G. but the data can be read immediately. Tutorial Questions 1. Use diagrams to show blocks on different types of secondary storage. (i. Disk capacity therefore doubled. A block on a disk is the sector. Explain the terms 'blocking factor' and inter-block gap. Block . RAM is arranged like a series of boxes. each one with its own address. Once data is placed in each box it remains until replaced by more. It is treated as a single unit in data transfer.e. A block device is one that stores information in fixed size blocks.
Types of optical disks:CD-ROM (compact disc . The primary use is to allow a part of memory to be reserved for used like an ordinary disk. It is small hardware memory .4 1/2" 700MB/80 minutes WORM (write once. DVD-ROM (digital video/versatile disk – read only memory – used to store movies.g. Campbell Copyright @ 2010 Updated Jan 2010 89 . Tutorial Questions 1. How do they differ from other disks? 2. Differentiate between magnetic disk and optical disk. Optical disks have more storage capacity than magnetic disks and are less susceptible to damage. calculators. Subsequent access if they occur will be fast. G. Data is recorded by laser burns and read by another laser of lower intensity detecting the pattern of light reflected from beam by surface of disk. This allows fast access to data that might be needed in the future. Operating System Concepts Mrs. How does a Blu-Ray disc differ from the regular DVD? 4.RAM disks A RAM disk is commonly used in data banks. Optical disk These are made up of a thin metal polymer compound. Caching – This is the process of reading something into memory. DVD R+. Discuss RAM disks. palm tops. if it is needed there is no need to read from the disk again as it is already in memory. It holds data that was recently accessed from secondary storage in anticipation of use in the near future. Cache memory works at the high speed of the processor. E. Disk caching Cache – a special area of memory available to the processor.magnetic molecules in disk surface aligned when heated by a laser beam. They are used to store both video and audio files.read only memory) . read many) EO (erasable optical) . This does not provide permanent storage. the internet via a phone line is slow compared to disk access. DVD R-? 3.sometimes called associative registers. therefore the web page is downloaded to disk and used from the disk instead of viewing the data over the phone line. but once files have been copied to this area they can be accessed extremely quickly. Disk caching – This is the process of placing data onto the disk so that possible future access to this data is faster. What is the difference between DVD R.
G. Describe disk caching. What is a cookie? What is its purpose? 2. Operating System Concepts Mrs.Tutorial Questions 1. Campbell Copyright @ 2010 Updated Jan 2010 90 .
It is important that the disk be as fast as possible. The coating however will wear after enough use. Campbell Copyright @ 2010 Updated Jan 2010 91 . Thus the disk itself is cheaper to produce and use. Tracks are concentric circles on which data is stored. sector etc. To improve the performance of a disk. amount of information to be transferred Practice MCQs 1. In order to access data from moving-head magnetic disk storage. The disk also has to rotate to the appropriate sector. The operating system can improve on the average disk service time by scheduling the requests for disk access. G.Lecture 21 . cylinder. the read/write head has to move to the appropriate track.g. Sectors are pie-sliced sections (blocks) that are read all at once. Head crash . the head scrapes the recording media off the disk therefore destroying the data.if the read/write head touches the disk surface (e.) 3.Moving-head disk storage (2 hours) Operations on moving-head disk storage In Fundamentals of Information Technology. you learnt about tracks and sectors on magnetic disk. The read/write head is therefore positioned over the appropriate data in order to access it. is this an input or output operation? 2. the disk address (drive. memory address 4. due to power-cut). surface. When a process needs I/O to or from disk it issues a system call to the operating system. designers did all of the following EXCEPT: a) Properly schedule the use of the disk b) Create fixed head disks c) Double disk capacity d) Eliminate seek time Operating System Concepts Mrs. The request specifies pieces of necessary information:1. Floppy disks have a hard coated surface so that the read/write head can sit directly on it without destroying the data.
G. Tutorial Questions 1. • Transfer time – the time taken for data to move between the disk and main memory. What is the time taken for a disk's read/write head to move to the appropriate track? a) Seek time b) Transfer time c) Latency time d) Track time Operating System Concepts Mrs. This is also known as rotational latency or rotational delay.The time required for a storage medium such as a disk to be positioned and for read/write heads to be properly located so that the desired data can be read or written. Is there a relationship between the speed of the disk and the price? Practice MCQs 1. This is also known as transfer rate. Other definitions • Positioning time .Measures of magnetic disk performance Disk speed composed of 3 parts:• Seek time – the time taken for the read/write head to move to the appropriate track • Latency time – the time taken for the disk to rotate to the desired sector (block). Research the speeds of various brands of hard disks. Campbell Copyright @ 2010 Updated Jan 2010 92 .
otherwise the request will be queued. G. a sweep out towards the outer edge of Operating System Concepts Mrs. For example. thus moving backwards and forwards across the surface of the disk to get to the next requested location each time. SCAN and C-SCAN The read/write head starts at one end of disk (outermost cylinder) and moves toward the other end (innermost cylinders). For example. At the other end it reverses direction. servicing requests as it reaches each track. satisfying requests. when the read/write head reaches the end of the disk it goes immediately to the start of the disk. If the disk drive is available it will service a user's request immediately. As soon as the disk is available the user job to use the disk next will be selected by a disk scheduling algorithm. The movement time should be less than FCFS but the policy is fairer than SSTF. This policy will have better throughput than FCFS but a request may be delayed for a long period if many closely located requests arrive just after it. sharing the resource between the processes fairly and efficiently.Disk scheduling In multi-programming environment different processes may want to use the system's resources simultaneously. The movement across the surface of the disk is still apparently random but the time spent in movement is minimised. the drive sweeps across the surface of the disk. Since no reordering of request takes place the head may move almost randomly across the surface of the disk. in alternating directions. This method is fair but suffers from wild swings from one area of disk to another. No requests are serviced on the reverse direction. Circular Scan or C-SCAN is similar to SCAN but I/O requests are only satisfied when the read/write head is travelling in one direction across the surface of the disk. This policy aims to minimise response time with little regard for throughput. However the drive now makes use of the information it has about the locations requested by the waiting requests. processes will contend to access an auxiliary storage device such as a disk. LOOK and C-LOOK LOOK is similar to SCAN. It however may cause starvation of some requests. Campbell Copyright @ 2010 Updated Jan 2010 93 . until it gets to other end of disk. In other words. Each time an I/O request has been completed the disk controller selects the waiting request whose sector location is closest to the current position of the head. Disk scheduling algorithms include:First come first served (FCFS) The disk controller processes the I/O requests in the order in which they arrive. The disk drive needs some mechanism to resolve this contention. It services jobs that require data closest to the current head position. Shortest seek time first (SSTF) This is the most common algorithm.
If the queue of requests is 8. Thus it may curtail a sweep towards the outer edge when there are locations requested in cylinders beyond the current position. C-LOOK involves the drive head sweeping across the disk satisfying requests in one direction only. 147. 22. Suppose a disk drive has 200 cylinders. 22. 73. which is in great demand. 73. Tutorial Questions 1. 35.5. 73. and where to commence the next sweep. 5. The drive is currently servicing a request at cylinder 143 and the previous request was at cylinder 125. Which algorithm is known as the elevator algorithm? Why? 6. if that is the most central one for which a sector is currently requested. 60. 46. The queue of pending requests in FIFO order is 86. 80 b) 46. 46. 48. Practice MCQs 1. 22 Operating System Concepts Mrs. 22. Suppose the read/write head of a moving head disk with 10 tracks numbered 0-9 is currently servicing a request at track 9. and commence its next sweep at a cylinder which is not the innermost one.3. Campbell Copyright @ 2010 Updated Jan 2010 94 . 46.the disk will be reversed when there are no waiting requests for locations beyond the current cylinder. As in LOOK the drive makes use of the location of waiting requests in order to determine how far to continue a sweep. 17. 80. numbered 0 to 199. Sector queuing is an algorithm for fixed-head devices. What is the difference between SCAN and C-SCAN? Answer tutorial question # 2 using CSCAN. Explain two (2) methods that can be used by the operating system to schedule the usage of a hard disk on a server. Circular LOOK (C-LOOK) is based on C-SCAN. SCAN and SSTF algorithms? 4. Starting from its current head location what is the disk arm movement to satisfy the requests using FCFS. If the queue of requests is 80. 2. Explain how it works. G. 46 d) 73. 80 c) 73. 91. 80. Suppose the read/write head of a moving head disk with 100 tracks numbered 0 to 99 is currently servicing a request at track 62 and has just finished track 70.1: what is the head movement to satisfy the SCAN algorithm? 3. what is the head movement to satisfy the SSTF disk scheduling algorithm? a) 22.
Lecture 22 – RAID (2 hours)
RAID was first defined in 1987 to describe a redundant array of inexpensive disks. This technology allowed computer users to achieve high levels of storage reliability from low-cost and less reliable PC-class disk-drive components, via the technique of arranging the devices into arrays for redundancy. Marketers representing industry RAID manufacturers later reinvented the term to describe a redundant array of independent disks as a means of dissociating a "low cost" expectation from RAID technology. RAID is now used as an umbrella term for computer data storage schemes that can divide and replicate data among multiple hard disk drives. The different schemes/architectures are named by the word RAID followed by a number, as in RAID 0, RAID 1, etc. RAID's various designs involve two key design goals: increase data reliability and/or increase input/output performance. When multiple physical disks are set up to use RAID technology, they are said to be in a RAID array. This array distributes data across multiple disks, but the array is seen by the computer user and operating system as one single disk. RAID levels The standard RAID levels are a basic set of RAID configurations and employ striping, mirroring, or parity. A RAID 0 (also known as a stripe set or striped volume) splits data evenly across two or more disks (striped) with no parity information for redundancy. RAID 0 was not one of the original RAID levels and provides no data redundancy. RAID 0 is normally used to increase performance, although it can also be used as a way to create a small number of large virtual disks out of a large number of small physical ones. A RAID 0 can be created with disks of differing sizes, but the storage space added to the array by each disk is limited to the size of the smallest disk. For example, if a 120 GB disk is striped together with a 100 GB disk, the size of the array will be 200 GB. A RAID 1 creates an exact copy (or mirror) of a set of data on two or more disks. This is useful when read performance or reliability are more important than data storage capacity. Such an array can only be as big as the smallest member disk. A classic RAID 1 mirrored pair contains two disks (see diagram), which increases reliability geometrically over a single disk. Since each member contains a complete copy of the data, and can be addressed independently, ordinary wear-and-tear reliability is raised by the power of the number of self-contained copies.
Operating System Concepts Mrs. G. Campbell Copyright @ 2010
Updated Jan 2010
A RAID 2 stripes data at the bit (rather than block) level, and uses a Hamming code for error correction. The disks are synchronized by the controller to spin in unison. Extremely high data transfer rates are possible. This is the only original level of RAID that is not currently used. The use of the Hamming(7,4) code (four data bits plus three parity bits) also permits using 7 disks in RAID 2, with 4 being used for data storage and 3 being used for error correction. RAID 2 is the only standard RAID level, other than some implementations of RAID 6, which can automatically recover accurate data from single-bit corruption in data. Other RAID levels can detect single-bit corruption in data, or can sometimes reconstruct missing data, but cannot reliably resolve contradictions between parity bits and data bits without human intervention. (Multiple-bit corruption is possible though extremely rare. RAID 2 can detect but not repair double-bit corruption.) All hard disks soon after implemented an error correction code that also used Hamming code, so RAID 2's error correction was now redundant and added unnecessary complexity. Like RAID 3, this level quickly became useless and it is now obsolete. There are no commercial applications of RAID 2. A RAID 3 uses byte-level striping with a dedicated parity disk. RAID 3 is very rare in practice. One of the side effects of RAID 3 is that it generally cannot service multiple requests simultaneously. This comes about because any single block of data will, by definition, be spread across all members of the set and will reside in the same location. So, any I/O operation requires activity on every disk and usually requires synchronized spindles. In the example shown, a request for block "A" consisting of bytes A1-A6 would require all three data disks to seek to the beginning (A1) and reply with their contents. A simultaneous request for block B would have to wait. However, the performance characteristic of RAID 3 is very consistent, unlike higher RAID levels, the size of a stripe is less than the size of a sector or OS block so that, for both reading and writing, the entire stripe is accessed every time. The performance of the array is therefore identical to the performance of one disk in the array except for the transfer rate, which is multiplied by the number of data drives (i.e., less parity drives).
Operating System Concepts Mrs. G. Campbell Copyright @ 2010
Updated Jan 2010
This makes it best for applications that demand the highest transfer rates in long sequential reads and writes, for example uncompressed video editing. Applications that make small reads and writes from random places over the disk will get the worst performance out of this level. The requirement that all disks spin synchronously (in lockstep), added design considerations to a level that did not give significant advantages over other RAID levels, so it quickly became useless and is now obsolete. Both RAID 3 and RAID 4 were quickly replaced by RAID 5. However, this level has commercial vendors making implementations of it. It's usually implemented in hardware, and the performance issues are addressed by using large disk caches. A RAID 4 uses block-level striping with a dedicated parity disk. This allows each member of the set to act independently when only a single block is requested. If the disk controller allows it, a RAID 4 set can service multiple read requests simultaneously. RAID 4 looks similar to RAID 5 except that it does not use distributed parity, and similar to RAID 3 except that it stripes at the block level, rather than the byte level. Generally, RAID 4 is implemented with hardware support for parity calculations, and a minimum of 3 disks is required for a complete RAID 4 configuration. In the example, a read request for block A1 would be serviced by disk 0. A simultaneous read request for block B1 would have to wait, but a read request for B2 could be serviced concurrently by disk 1. Unfortunately for writing the parity disk becomes a bottleneck, as simultaneous writes to A1 and B2 would in addition to the writes to their respective drives also both need to write to the parity drive. In this way RAID example 4 places a very high load on the parity drive in an array. The performance of RAID 4 in this configuration can be very poor, but unlike RAID 3 it does not need synchronized spindles. However, if RAID 4 is implemented on synchronized drives and the size of a stripe is reduced below the OS block size a RAID 4 array then has the same performance pattern as a RAID 3 array. Both RAID 3 and RAID 4 were quickly replaced by RAID 5. A RAID 5 uses block-level striping with parity data distributed across all member disks. RAID 5 is popular because of its low cost of redundancy. This can be seen by comparing the number of drives needed to achieve a given capacity. RAID 1 or RAID 1+0, which yield redundancy, give only s / 2 storage capacity, where s is the sum of the capacities of n drives used. In RAID 5, the yield is
Operating System Concepts Mrs. G. Campbell Copyright @ 2010 Updated Jan 2010
A simultaneous read request for block B1 would have to wait. Operating System Concepts Mrs.which function as a slow RAID-1. Describe the standard RAID levels. it can also be done at the operating system level. G.g. Describe the non-standard RAID levels. but the same four drives can be used to build a 3-TB array under RAID 5. while mdadm supports a fully-functional (non-degraded) RAID 5 setup with two disks . Performance varies greatly depending on how RAID 6 is implemented in the manufacturer's storage architecture – in software. Although RAID 5 is commonly implemented in a disk controller. Discuss the term RAID. but can be expanded with further volumes. Campbell Copyright @ 2010 Updated Jan 2010 98 . 2. Describe the failure rate and performance of each RAID level. but it does have a performance penalty on write operations because of the overhead associated with parity calculations. firmware or by using firmware and specialized. using Windows Dynamic Disks or with mdadm in Linux. but a read request for B2 could be serviced concurrently by disk 1. RAID 6 does not have a performance penalty for read operations. e. four 1TB drives can be made into a 2-TB redundant array under RAID 1 or RAID 1+0. As an example. In the example. some with hardware support for parity calculations (hardware RAID cards) and some using the main system processor (motherboard based RAID controllers). Tutorial Questions 1. In some implementations a degraded RAID 5 disk set can be made (three disk set of which only two are online).. 3.where Smin is the size of the smallest disk in the array. 4. a read request for block A1 would be serviced by disk 0. A minimum of three disks is required for a complete RAID 5 configuration.
Father. Incremental – backup that copies only the files that have changed since the last full or last incremental backup. The following describes the different types of backup. the son becomes the father and the new backup becomes the son. G. The oldest backup is called the grandfather. then the entire backup is useless. the middle backup is the father and the latest backup is called the son.save to CD 1 etc.save to CD 3 (Son) • Day 4 . Operating System Concepts Mrs.if one change is messed up. Campbell Copyright @ 2010 Updated Jan 2010 99 . Differential – backup that copies only the files that have changed since the last full backup Selective – backup that allows a user to choose specific files to back up. dry. Disadvantage .restore the main backup first. A backup is a duplicate of a file.Lecture 23 – Backup and recovery methods (1 hour) Backup is the key – the ultimate safeguard Regardless of the precautions that you take. son technique for magnetic tape • Keep 3 tapes/CDs/DVDs etc • You will always have the last 3 days backups • Day 1 . then changes since (incremental backup). or destroyed. damaged. If your computer fails you can restore from the backup. or disk that can be used if the original is lost. regardless of whether or not the files have changed since the last backup Grandfather. In order to recover you restore all files. Backup is therefore the main risk management solution.cool. father. Son (or Three-generation backup) – backup method in which you recycle 3 sets of backups. Restore newest/last tape/disk Backup of changes to audit files. It is laborious to restore at a point in time.save to CD 1 (Grandfather) • Day 2 .save to CD 2 (Father) • Daye 3 . things can still go wrong. To restore . then each incremental backup in the same sequence. clean location • Do not put disks in the sun • Do not put magnetic backup media near magnets • Restore data every now and again to ensure disk/tape still good and backup will be available in emergency. Each time that you backup you reuse the oldest backup medium. • • • • Grand father. Restore changes from audit. • • Full – backup that copies all of the files in a computer (also called archival backup). Backup all files (main backup). This method allows you to have the last 3 backups at all times. The father then becomes the grandfather. Backup Tips • Always Label backups with a felt tip pen • Store disk/tape in proper place .
Which backup method should John use? a) Differential b) Generation c) Incremental d) Selective 4. Describe how to restore based on the different backup methods. Did you have to type everything over)? 5. 2. John would like to create a CD with all of his lecture notes for the semester. 6. G. How would you recover using a generation backup? a) Use the oldest backup b) Use the latest backup c) Use the last full backup and the oldest backup d) Use the last full backup and the latest backup 5. Tutorial Questions 1. why did you have to? Have you ever lost valuable data because you did not have a backup? Describe the situation. Which backup method copies only the files that have changed since the last full backup? a) Differential b) Generation c) Incremental d) Selective 3. Discuss the time limit for thumb drives. 3.• Keep a backup offsite in case something happens to the current location such as a fire.g. then each incremental backup in sequence b) Use the last full backup first then the last incremental backup c) Use the last generation backup then the previous backup d) Use the last incremental backup Operating System Concepts Mrs. Do you backup? If yes. How did you solve the problem (e. Campbell Copyright @ 2010 Updated Jan 2010 100 . Practice MCQs 1. How would you recover from an incremental backup? a) Use the last full backup first. why not? What type of backup do you perform? What backup medium do you use? Have you ever had to restore a backup? If yes. A backup procedure that saves only files that have changed is a) Main backup b) Preferential backup c) Differential backup d) Incremental backup 2. how often do you back up? If not. 4.
Discuss the concept of a file server. Operating System Concepts Mrs. Often clients and servers operate over a computer network on separate hardware. A file server is usually not performing any calculations. Every access to a remote file may require a considerable amount of message transfer overhead.) 4. Clients therefore initiate communication sessions with servers which await (listen to) incoming requests. Differentiate between the peer-to-peer and the client-server architecture? 2. The operating system automatically converts accesses to shared (non-local) files into messages to the file server.g. All shared files reside at this single centralized site. Discuss the other types of servers (e. Campbell Copyright @ 2010 Updated Jan 2010 101 . A client does not share any of its resources. mail server. The term server highlights the role of the machine in the client-server scheme. A file server is a high-performance computer attached to a network that has the primary purpose of providing a location for the shared storage of computer files that can be accessed by the workstations that are attached to the computer network. the location of a file is transparent to users. G. but requests a server's content or service function.Lecture 24 . It runs one or more server programs which share its resources with clients. who access remote files in the same way as local files.File server systems (1 hour) Client-server computing or networking is a distributed application architecture that partitions tasks or workloads between service providers (servers) and service requesters. and does not run any programs on behalf of the clients. The main problem with this scheme is that the file server may become a bottleneck. where the clients are the workstations using the storage. print server etc. the open request is channelled to the file server. If a user opens a non-local file. database server. Detail the specifications of a server that would be required by the college in order to adequately service the students using the labs. In this scheme. 3. The files can be downloaded or manipulated in some manner by a client. It is designed primarily to enable the rapid storage and retrieval of data where the heavy computation is provided by the workstations. called clients. Tutorial Questions 1.
regardless of where they reside? o Locality . Dynamic. the data can exist on various file servers on the network. • Can expose correspondence between component units and machines. • In a conventional file system. • File name still denotes a specific. sector>. • This is a convenient way to share data. the data does not all have to reside in one place as in a centralized system. on files. it's understood where the file actually resides. G. Operating System Concepts Mrs. Location transparency • The name of a file does not reveal any hint of the file's physical storage location. The file location may or may not be transparent to the user. A local file can be accessed by a user residing on any site in the system. Resources on other machines are remote. • In a transparent DFS.Does a user access all of the files in a system in the same manner. Location independence • The name of a file does not need to be changed when the file's physical storage location changes. In a networked environment users want to share data files. • Separates the naming hierarchy from the storage devices hierarchy. read. although hidden. A distributed file system (DFS) consists of software that keeps track of files stored across multiple servers or networks. The resources on a particular machine are local to itself. There are two major issues that dominate the design criteria in a distributed file system:o Transparency . • File replication means multiple copies of a file. the location of a file. the system and disk are known. • Better file abstraction.Where do files reside in the system? Each site maintains its own local file system. mapping returns a SET of locations for the replicas. When data are requested. • Example: A user filename maps to <cylinder. one-to-many mapping. The server interface is the normal set of file operations: create.Lecture 25 . The purpose is to promote sharing of dispersed files. Campbell Copyright @ 2010 Updated Jan 2010 102 . a DFS converts the file names into the physical location of the files so they can be accessed.Distributed file systems (1 hour) A Distributed File System (DFS ) is simply a classical model of a file system distributed across multiple machines. somewhere in the network. A file system provides a service for clients. set of physical disk blocks. You may also split the files by rows/columns on different servers. Naming is the mapping between logical and physical objects. • Promotes sharing the storage space itself. is hidden. etc.
Discuss the advantages and disadvantages of a distributed file system. Campbell Copyright @ 2010 Updated Jan 2010 103 . includes the file's logical storage location C. G.Most DFSs today: • Support location transparent systems. In the naming structure of a file if location transparency is used what happens? File name: A. • Do NOT support migration. Practice MCQs 1. reveals the file's physical storage location B. (automatic movement of a file from machine to machine. Research and give examples of various DFSs. does not reveal the file's physical storage location D. Distinguish between a centralized versus a distributed system.) • Files are permanently associated with specific disk blocks. 2. Tutorial Questions 1. 3. reveals the file's logical storage location Operating System Concepts Mrs.
E. Advantages • The co-processor is often designed to do certain tasks more efficiently than the main processor. Operating System Concepts Mrs. the time taken to perform an entire job will be largely constrained by the CPU. • Co-processors allow a line of computers to be customized.375E -3) . Campbell Copyright @ 2010 Updated Jan 2010 104 .g. Disadvantages • Some co-processors cannot fetch instructions from memory. What is the co-processor used to do in this particular computer.Co-processors (1/4 hour) A single CPU works in conjunction with specialized "slave" processors that perform dedicated chores/tasks. The decimal point is moved/floated along the digits to a position in between first or second non-zero most significant digit.375 x 10-3 (1. coprocessors can accelerate system performance. resulting in far greater speeds for the computer as a whole.375 x 101 (1. A more common use was to control input/output channels. 10 = base/radix. 2. Many Micro-computers today have slave processors that handle tasks such as high speed mathematical computation. Coprocessors were first seen on mainframe computers.screen graphics. These processors require the host main processor to fetch the coprocessor instructions and handle all other operations aside from the coprocessor functions • Co-processors carry out only a limited range of functions Tutorial Questions 1. G.001375 = 1.75 = 1. E. A co-processor is therefore a microprocessor that performs specialized functions that the central processing unit cannot perform or cannot perform as well and as quickly. execute program flow control instructions. display .Lecture 26 . Identify a computer that uses a co-processor.g. manage memory etc. so that customers who do not need the extra performance need not pay for it. Describe the different types of co-processors in use in modern computers. where they added additional "optional" functionality such as floating point math support. Math Co-processors This is a separate processor that handles floating point (real numbers). and keyboard operations. do input/output operations. At any point in time two or more processors within the system unit may be performing work simultaneously.375 = mantissa/argument. -3 = characteristic or exponent. 13. However. • By offloading processor-intensive tasks from the main processor.375E +1) .
'superscalar'.3. 4. Discuss the advantages and disadvantages of co-processors. Practice MCQs 1. Explain the concepts: 'pipelining'. 'dual-core'. Campbell Copyright @ 2010 Updated Jan 2010 105 . G. What is a co-processor? a) A processor that works for another processor b) A processor that is in charge of another processor c) A processor that works alongside another processor d) The main processor in a micro-computer Operating System Concepts Mrs.
MOVE. E. number of registers. (More instructions per clock cycle). In removing the complexity in the way that the processor is designed some instructions are removed. E. On these machines. doing arithmetic. Campbell Copyright @ 2010 Updated Jan 2010 106 . JUMP and carrying them out as a series of little steps. RISC. In other words. and the number of clock cycles needed to execute an instruction. RISC (Reduced instruction set computing) A RISC processor is a type of microprocessor that recognizes a relatively limited number of instructions. This software. IBM RS 6000 and those based on the MIPS chip or using SUN SPARC architecture. however the differences extend further. addressing modes.Lecture 27 .g. Until the mid-1980s. Some computers. At that time. fetching the machine language instructions such as ADD. Some machines have a layer of primitive software that directly controls the hardware and provides an interface between the hardware and operating system. called the micro-program (or firmware). A RISC program is therefore longer than the equivalent CISC and takes up more storage space. however. It is often assumes that these designs differ based on the size of the instruction sets. Two basic computer design philosophies predominant in the market today are the complex instruction set and the reduced instruction set.reduced instruction set computer. Operating System Concepts Mrs. These have fewer instructions in their instruction set. the hardware executes the machine language instructions directly. These designs also differ in their instruction lengths. Multiplication is the equivalent of a repeated addition. and comparing values. This is the normal type of computer. is usually located in ROM (read only memory). They take many clock cycles to complete one instruction. Introduction to RISC and CISC CISC . RISC .RISC/CISC (3/4 hour) What is an Instruction set? An instruction set is the set of available instructions that the computer can understand and perform. There is still considerable controversy among experts about the ultimate value of RISC architectures. RISC makes the processor simple (non complex) so that they can execute more instructions in the same amount of time. a number of computer manufacturers decided to reverse this trend by building CPUs capable of executing only a very limited set of instructions. The machine language typically has between 50 and 300 instructions mostly for moving data around the machine. it lists the things that the processor can do. the tendency among computer manufacturers was to build increasingly complex CPUs that had larger sets of instructions. do not have a microprogramming level. It is actually an interpreter.g. G.complex instruction set computer.
and make them cheaper to manufacture. advanced compilers.P. most RISC microprocessors have floating-point units (FPUs) built in. Only load and store instructions access memory . the computer would get more done in a shorter amount of time. G.In the mid 1970s. developments in technology made RISC attractive to computer designers. Pipelining allows the next instruction to enter the execution cycle while the previous instruction is still processing. Typically. Since almost all instructions make use of register addressing. Updated Jan 2010 Operating System Concepts Mrs. Campbell Copyright @ 2010 107 . and begins execution of the corresponding code. Some of these developments were great increases in memory size with corresponding decreases in cost. It "guesses" whether or not the condition will be met. high-speed caches. For this reason. it has gained time. These instructions consist mostly of register-to-register operations . RISC microprocessor (Microprocessor without Interlocked Pipe Stages). Due to these developments. The latter CPU led to the founding of MIPS Technologies. unlike complex instruction set machine. and better pipelining. RISC microprocessors also emphasize floating-point performance making them popular with the scientific community whose applications do more floating-point math. it does not wait to see if the condition has been met. who developed the M. IBM designed the first reduced instruction set computer. Pipelining was a key technique in achieving this. If the processor guessed correctly. The RISC concept was used to simplify the design of the IBM PC/XT. If the processor has fetched a branch instruction. making the other 80% superfluous to requirement. For example. there are only a few addressing modes in a reduced instruction set computer and there are a large number of general-purpose registers. If the processor has guessed incorrectly. which would require fewer transistors1. Reduced instruction set machines.S. RISC architecture makes use of a small set of simplified instructions in attempt to improve performance. Advantages of RISC • 1 They can execute their instructions very fast because the instructions are so simple. The concept was developed by John Cocke of IBM Research during 1974. A processor based upon this concept would use few instructions. a reduced instruction set computer stores its instruction in 32 bits. Another way in which reduced instruction set computers sought to improve performance was to have most instructions complete execution in one machine cycle. By reducing the number of transistors and instructions to only those most frequently used. use same length instructions so that the instructions are aligned on word boundaries and may be fetched in a single operation. and was later used in the IBM RISC System/6000 and Sun Microsystems SPARC microprocessors.I. the results are discarded and there is no loss. a PowerPC has 32 registers. The transistor is a solid-state electronic device used primarily for switching and amplification. His argument was based upon the notion that a computer uses only 20% of the instructions. Many of the MIPS architects also played an important role in the creation of the Motorola 68000. Another technique utilized by reduced instruction set machines is pre-fetching coupled with speculative execution .
Another major setback was the presence of Intel.• • RISC chips are simpler as they require fewer transistors. The price of RAM has decreased dramatically. By 1994. RISC architectures put a greater burden on the software. the differences were not great enough to persuade buyers to change technologies.1 and Windows 95 were designed with CISC processors in mind. Programmer must pay close attention to instruction scheduling so that the processor does not spend a large amount of time waiting for an instruction to execute Debugging can be difficult due to the instruction scheduling Require very fast memory systems to feed them instructions RISC chips require more lines of code to produce the same results and are increasingly complex. Without commercial interest. so that the RISC use of RAM and emphasis on software has become ideal. the Intel x86 is arguable the only chip which retains CISC architecture. Campbell Copyright @ 2010 108 . Intel had the resources to plow through development and produce powerful processors. Many companies were unwilling to take a chance with the emerging RISC technology. RISC developers have also failed to remain in competition with CISC alternatives. Compiler technology has also become more sophisticated. This will increase the size of the application and the amount of overhead required.000. To some extent. Despite the advantages of RISC based processing. processor developers were unable to manufacture RISC chips in large enough volumes to make their price competitive. Despite the speed advantages of the RISC processor. Updated Jan 2010 Operating System Concepts Mrs. the same amount of memory cost only $6 (when adjusted for inflation). This was largely due to a lack of software support. G. which makes them cheaper to design and produce. Although their CISC chips were becoming increasingly unwieldy and difficult to develop. it cannot compete with a CISC CPU that boasts twice the number of clock cycles. In 1977. The Macintosh market has been damaged by several problems that have affected the availability of 500MHz+ PowerPC chips. Many of today's RISC chips support as many instructions as yesterday's CISC chips. This is primarily due to advancements in other areas of computer technology. producing faster and cheaper processors . the PC compatible market has stormed ahead and has broken the 1GHz barrier. Instructions are executed over 4x faster providing a significant performance boost! Today. Although RISC chips might surpass Intel's efforts in specific areas.an Apple Mac G3 offers a significant performance advantage over its Intel equivalent. RISC supporters argue that it the way of the future. They argue that this is not worth the trouble because conventional microprocessors are becoming increasingly fast and cheap anyway. Although Apple's Power Macintosh line featured RISC-based chips and Windows NT was RISC compatible. the argument is becoming moot because CISC and RISC implementations are becoming more and more alike. Disadvantages of RISC • • • • • • • • • Skeptics note that by making the hardware simpler. RISC chips took over a decade to gain a foothold in the commercial world. And today's CISC chips use many techniques formerly associated with RISC chips. In contrast. Windows 3. 1MB of DRAM cost about $5.
Windows NT. Ultra2 and SPARCcluster. Apple introduced the Power Mac.Examples of RISC Processors Power Mac In 1994. The first computers based on the PowerPC architecture were the Power Macs. Campbell Copyright @ 2010 Updated Jan 2010 109 . MIPS Another computer classified as having a reduced instruction set. Alpha Processor A powerful RISC processor developed by Digital Equipment Corporation and used in their line of workstations and servers. The term SPARC® itself is a trademark of SPARC International. all instructions are 32-bits in length. It contains many general-purpose registers (32 in all) and a floating-point unit. Apple Computer. which appeared in 1994. Since the unbundling of ARM from Acorn. including IBM. There are already a number of different operating systems that run on PowerPC-based computers. including the Macintosh operating system (System 7. and OS/2. an independent organization that licenses the term to Sun for its use. Pre-fetching and speculative execution are other methods the PowerPC uses to speed execution of instructions. Performance Optimization With Enhanced RISC. have built PCs based on the PowerPC. G. based on the PowerPC RISC microprocessor. a RISC technology developed by Sun Microsystems. Ultra1. Another RISC feature of the SPARC is that only load and store instructions are allowed to access memory. John Cocke created the 801 prototype microprocessor (1975).5 and higher). and Motorola Corporation. Their ARM and StrongARM chips power the old Acorn Archimedes and the Apple Newton handwriting recognition systems. A Power PC chip is A RISC -based computer architecture developed jointly by IBM. ARM One of the most well known RISC developers is Cambridge based Advanced Research Machines (originally Acorn Research Machines). SPARC Short for Scalable Processor Architecture. other manufacturers. SPARCserver. Sun's workstations based on the SPARC include the SPARCstation. It also takes advantage of pipelining to approach the goal of one instruction per clock cycle. becoming the first RISC microprocessor. 801 To prove that his RISC concept was sound. Since then. . The name is derived from IBM's name for the architecture. It was never marketed but plays a pivotal role in computer history. Arithmetic operations are performed only on values in the registers. RISC 1 and 2 The first "proper" RISC chips were created at Berkeley University in 1985. In the SPARC. Intel has invested a considerable amount of money in the company and have utilized the technology in their processor Operating System Concepts Mrs.
Variable-length instructions were used to limit the amount of wasted space. and stands for complex instruction set computer. Most personal computers. microcode acts as a transition layer between the instructions and the electronics of the computer. and a micro-programmed design can be easily modified to handle new instruct ions sets. CISCbased systems still cover the vast majority of the consumer desktop market. CISC Since the emergence of RISC computers. is RISC (reduced instruction set computer). CISC chips have a large amount of different and complex instruction. The majority of these systems are based upon the x86 architecture or a variant. although these instructions did require multiple clocks cycles to execute. However. One of the main advantages for the ARM is the price. G. This also improved performance. use a CISC architecture. the ROM contains a group of microcode instructions that correspond with each machine-language instruction. At that time. An alternative architecture.it costs less than £10. used by many workstations and also some personal computers. The argument for its continued use indicates that the chip designers should make life easier for the programmer by reducing the amount of instructions required to program the CPU. In a nutshell. In contrast to RISC. CISC philosophy used microcode to simplify the computer's architecture. which supports fewer instructions. The first instruction had to complete the execution cycle before the next instruction could begin. Due to the high cost of memory and storage CISC microprocessors were considered superior due to the requirements for small. This reduced the amount of time spent retrieving instructions from memory. The Amiga. computers executed instructions sequentially. easier implementation of new chips. although they do require special decoding circuits that count bytes within words and frame the instructions 2 Firmware Updated Jan 2010 Operating System Concepts Mrs. it executes the corresponding series of microcode instructions. conventional computers have been referred to as CISCs (complex instruction set computers). in which the CPU supports as many as two hundred instructions. and pre-1994 Macintosh systems also use a CISC microprocessor. Designers combined sequences of instructions into single instructions. When a machine-language instruction arrives at the processor. code size has become a non-issue. Another characteristic of complex instructions set is their variable-length instruction format. Pronounced sisk. Complex instructions came about in order to maximize the performance of early computers. Atari. they would possibly have used the chip to power the low-end Amigas. In a microprogrammed2 system. fast code. since instructions could be retrieved up to ten times faster from ROM than from main memory.design. CISC (Complex Instruction Set Computer) is a retroactive definition that was introduced to distinguish the design from RISC microprocessors. If Samsung had bought the Amiga in 1994. In an age of dwindling memory hard disk prices. Campbell Copyright @ 2010 110 . Other advantages of using microcode included fewer transistors.
This is caused by one factor that the RISC manufacturers have no influence over . A large number of addressing modes also characterizes complex instruction set computers. has the following modes: to/from a register. since earlier generations of a processor family were contained as a subset in every new version Different instructions take different amount of time to execute due to their variablelength Many instructions are not used frequently. However. no need to hardwire a control unit Upwardly compatible because a new computer would contain a superset of the instructions of the earlier computers Fewer instructions could be used to implement a given task. Variables Updated Jan 2010 Operating System Concepts Mrs. allowing for more efficient use of memory Simplified compiler. Due to the large number of addressing modes.according to their byte length. since the instructions are not a fixed size Disadvantages of CISC Instruction sets and chip hardware became more complex with each generation of computers. creating a demand from people who have not • • • • • • • • • 3 Parameters. binary and arithmetic operations have two or three operands3. In the VAX. to/from an address offset from a base address in memory. while string operations have three or five operands. to/from a specific location in memory. G. Campbell Copyright @ 2010 111 . CISC microprocessors are more expensive to make than their RISC cousins. In particular. an example of a complex instruction set computer. which can operate directly on memory. Approximately 20% of the available instructions are used in a typical program As discussed above. Another characteristic of the CISC design philosophy is the small number of general-purpose registers. the Intel market has become the definition of personal computing. etc.market factors. typically about 8 registers.000 versions of integer add in the VAX. because the micro-program instruction sets could be written to match the constructs of high-level languages More instructions can fit into the cache. Advantages of CISC Less expensive due to the use of microcode. to/from an address pointed to by a memory location. The VAX. there are more than 30. to/from an address offset from a base address in a register. This is a result of having instructions. to/from an address pointed to by a register. the average Macintosh is more expensive than the Intel PC.
used a computer previous. The x86 market has been opened by the development of several competing processors, from the likes of AMD, Cyrix, and Intel. This has continually reduced the price of a CPU of many months. In contrast, the PowerPC Macintosh market is dictated by Apple. This reduces the cost of x86 based microprocessors, while the PowerPC market remains stagnant. Examples of CISC Processors/Chips VAX The VAX is one example of a CISC. It has a large number of addressing modes. Another CISC characteristic it exhibits is variable-length instructions. Binary and arithmetic operations require 2 or 3 operands, but string operations need 3 or 5 operands . Motorola 68000 Another computer family that is classified as a complex instruction set computer is the Motorola 68000 family. It contains few general-purpose registers: 8 data registers and 8 address registers. It also uses variable-length instructions. Each inst ruction in one of these computers requires 0, 1, or 2 operands. IBM370 and Intel line Other typical complex instruction set computers include the IBM 370 and Intel's 80x86 line of computers.
CRISC Complex instruction set computers (CISC) and reduced instruction set computers (RISC) have been combined to form a hybrid known as a Complex/Reduced instruction set Computer (CRISC). Today, the distinction between RISC and CISC is becoming rather fuzzy. The first hints of RISC technology began to appear in Intel's 80x86 processor in 1989, when the 486 had a FPU4, more hard-wired instruction logic, and pipelining. Other manufacturers have followed suit such as Cyrix. Cyrix's M1 also takes advantage of pipelining to increase instruction execution. The M1 has the same micro-architecture as the Intel 80x86 family of complex instruction set machines.. Another RISC characteristic the M1 has borrowed is a large number of general-purpose registers. The M1 has 32 general-purpose registers by using a technique called dynamic register naming, which makes it appear as if there are only 8 registers in use at a time. This preserves compatibility with existing software that expects to see only 8 registers. The Pentium is another CISC/RISC hybrid. It uses variable-length instructions and few generalpurpose registers as a complex instruction set computer would, but it adopts RISC-like features, pipelining and a floating-point unit. In the aftermath of the CISC-RISC conflict, a new enemy has appeared to threaten the peace. EPIC (Explicitly Parallel Instruction Computing) was developed by Intel for the server market, thought it will undoubtedly appear in desktops over the next few years. The first EPIC processor
Floating Point Unit
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Operating System Concepts Mrs. G. Campbell Copyright @ 2010
will be the 64-bit Merced. The market may be divided between combined CISC-RISC systems in the low-end and EPIC in the high-end. Summary/Conclusion Complex instruction set computers and reduced instruction set computers differ greatly. CISC has a large, complex instruction set, variable-length instructions, a large number of addressing modes, and a small number of general-purpose registers. On the other hand, RISC has a reduced instruction set, fixed-length instructions, few addressing modes, and many general-purpose registers. Today, designers are producing a hybrid of the two design philosophies known as a complex/reduced instruction set computer. These computers combine characteristics such as variable-length instructions, few general-purpose registers, pipelining, and floating-point units. As the world goes through the 21st century the CISC Vs. RISC arguments have been swept aside by the recognition that neither terms are accurate in their description. The definition of 'Reduced' and 'Complex' instructions has begun to blur, RISC chips have increased in their complexity (compare the PPC 601 to the G4 as an example) and CISC chips have become more efficient. The result are processors that are defined as RISC or CISC only by their ancestry. The PowerPC 601, for example, supports more instructions than the Pentium. Yet the Pentium is a CISC chip, while the 601 is considered to be RISC. CISC chips have also gained techniques associated with RISC processors. Intel describe the Pentium II as a CRISC processor, while AMD use a RISC architecture but remain compatible with the dominant x86 CISC processors. Thus it is no longer important which camp the processor comes from, the emphasis has onceagain been placed upon the operating system and the speed that it can execute instructions. The CISC approach attempts to minimize the number of instructions per program, sacrificing the number of cycles per instruction. RISC does the opposite, reducing the cycles per instruction at the cost of the number of instructions per program. Tutorial Questions 1. Write an algorithm to do multiplication of 2 numbers by doing a repeated addition. 2. Use a table to compare RISC to CISC. 3. Identify the different brands of RISC and CISC computers. Practice MCQs 1. The computer that executes more instructions in a clock cycle is a) FCFS b) RISC c) SCAN d) CISC 2. Which of the following is a feature of a RISC processor? a) Instructions consist mostly of register-to-register operations
Operating System Concepts Mrs. G. Campbell Copyright @ 2010 Updated Jan 2010
b) There is microcode that acts as a transition layer between the instructions and the computer c) Instructions have a variable-length format d) Instructions require multiple clocks cycles to execute 3. Which of the following is a feature of a CISC processor? a) Fewer transistors and cheaper to manufacture b) Most instructions complete execution in one machine cycle c) Designers have combined sequences of instructions into single instructions d) More problems for the programmer and longer programs 4. What is the reason for a processor chip having variable length instructions? a) To allow them to be fetched in a single operation b) To limit the amount of wasted space c) To reduce the need for micro-code d) To reduce the number of instructions
Operating System Concepts Mrs. G. Campbell Copyright @ 2010
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flood. personal history. Loss of computer and data.g.g. Disasters (Natural or otherwise) – earthquake. entering incorrect data. loss of time in having to re-enter data. delete a file by accident. young child) Technical error – system failure e. Loss of income due to software piracy. less data integrity (incorrect data) therefore incorrect information will be retrieved. This can lead to things like software piracy. Also leads to theft of intellectual property.g. G. or blackmail based on information gained from computerized files (e.Lecture 28 – Security (1 hour) Definition of security Computer security refers to techniques for ensuring that data stored in a computer cannot be read or compromised by any individuals without authorization. Loss of data. low voltage. or marketing plans). software. Theft. vandalism. Loss of files/data. Loss of time. Purpose of security The purpose of security is to either prevent a security risk from happening or to reduce its effects. A security risk is any event or action that could cause a loss of or damage to computer hardware.. Campbell Copyright @ 2010 115 .. May need to re-install software. civil disorder Competing entity could use data against your company. or processing capability. Updated Jan 2010 Operating System Concepts Mrs. insects Unauthorized use and access – hacker/cracker gets access illegally. Loss of sales due to piracy. adding data twice. Huge repair bill. Most security measures involve data encryption and passwords. power surges. medical information. fire. hard disk crash. loss of time. Physical damage to computer. hurricane. Damage to computer due to improper use. not adequately trained/experienced (e. Loss of computer. data. Loss of data.g. customer lists. Illegal access to files. information. Employees do things to deliberately modify the data. pricing data. lightening. Identity theft. Effect Loss of data. or sexual preference).g. booting file missing/corrupted Virus – program that causes damage to files or computer. theft of marketing information (e. Forms of security violation The following table indicates the different security risks and their effects. Category Human error – e.
a biological virus must inject its DNA into a cell. it is then able to infect other programs or documents.it is not alive. Unlike a cell. Computer viruses are called viruses because they share some of the traits of biological viruses. thereby allowing it to be read by unscrupulous persons. at times impossible to avoid despite the best efforts and often very costly to an organization's productivity. Worm A worm is a small piece of software that uses computer networks and security holes to replicate itself. Logic bomb A logic bomb is a type of virus that activates when certain sequence of activities are done on the computer. and then starts replicating from there. A computer virus shares some of these traits. such as causing a program to operate incorrectly or corrupting a computer's memory. The program also claims to do one thing (it may claim to be a game) but instead does damage when you run it (it may erase your hard disk). Campbell Copyright @ 2010 Updated Jan 2010 116 . Operating System Concepts Mrs. Example: a fake login screen will allow you to put in your id and password. In some cases. Viruses are the colds and flues of computer security: Ubiquitous (ever-present). A computer virus passes from computer to computer like a biological virus passes from person to person. Once it is running. In other cases. as well. the new virus particles bud off the cell one at a time. G. A biological virus is not a living thing. but there are enough similarities that the name sticks. Instead. releasing the virus. and the cell remains alive.Security threats and attacks Trojan Horse A Trojan appears to be something that it is not so that you give out certain information. Obviously. It may be benign or have a negative effect. The viral DNA then uses the cell's existing machinery to reproduce itself. A virus is a fragment of DNA inside a protective jacket. There are similarities at a deeper level. the analogy between computer and biological viruses stretches things a bit. It copies itself to the new machine using the security hole. Virus A computer program that is designed to replicate itself by copying itself into the other programs stored in a computer. A copy of the worm scans the network for another machine that has a specific security hole. the cell fills with new viral particles until it bursts. as well. Another example is a fake web site on which you give out your credit card information. A computer virus must piggyback on some other program or document in order to get executed. a virus has no way to do anything or to reproduce by itself -. Trojan horses have no way to replicate automatically.
An example of identification is using a password is a secret word or phrase that gives a user access to a particular program or system. hackers). so it can be understood.g. Encryption Data encryption is the translation of data into a form that is unintelligible without a deciphering mechanism. Tutorial Questions 1. Zone Alarm). Campbell Copyright @ 2010 Updated Jan 2010 117 . A distributed denial of service (DDOS) attack uses multiple computers throughout the network that it has previously infected. However. Some firewalls also protect systems from viruses and junk email (spam).Denial-of-service An assault on a network that floods it with so many additional requests that regular traffic is either slowed or completely interrupted.s of firewalls include: Black Ice. G. the correct decryption key is required. Identification is the act of claiming who you are. called a ciphertext. The computers act as "zombies" and work together to send out bogus messages. An example of authentication is fingerprint scanning. while authentication is proving it. McAfee. Firewall A firewall is a program and/or hardware that filters the information coming through the internet to prevent unauthorized access. Decryption is the process of converting encrypted data back into its original form. Virus protection. Authentication. which cannot be easily understood by unauthorized people (e. the password could have been guessed or secretly taken. Define the term cryptography. thereby increasing the amount of phony traffic. Firewall Authentication Authentication is a security measure designed to protect a communications system against fraudulent transmissions and establish the authenticity of a message. Norton Antivirus. Encryption is the conversion (encoding) of data into a form. Trend Micro-PCcillin). a denial of service attack interrupts network service for some period. Encryption.g. This must be updated regularly. Authorization is a process of allowing someone or something to do something based on the previous two.g. In order to easily recover the contents of an encrypted signal. Unlike a virus or worm. which can cause severe damage to databases. Operating System Concepts Mrs. (e. The key is an algorithm that undoes the work of the encryption algorithm. Virus protection Antivirus software (e.
John has gotten the system administrator password by accident but was not able to use it at his computer. Discuss various encryption software. Which security feature prevents a hacker from making sense out of files that he has gained access to? a) Encryption b) Firewall c) Inheritance d) Profile 3. What is a Virtual Private Network? Practice MCQs 1. What is the most popular security feature of operating systems? a) Biometric identification b) Directory encryption c) Time and location controls d) User ids and passwords 2. What security feature has been activated to limit John? a) Anti-virus b) Authority level c) Encryption d) Firewall 4. Describe the term Secure Socket Layer 6. What are your comments on becoming a certified ethical hacker? Visit the website http://www.2. 5. Campbell Copyright @ 2010 Updated Jan 2010 118 . G. Differentiate between Symmetric and Asymmetric Encryption 4. John has a password to the human resource system. He is able to view all employee data except salary.org/ 3. What security feature has been activated to prevent John from using this password? a) Administrative protection b) Authority level c) Location control d) Password blocking Operating System Concepts Mrs.eccouncil.
multitasking UNIX-type operating system that is open source software. Read. If someone knows that the file is there or lists hidden files. Each user has a certain level of access rights or authority on different files and directories. DOS used a command-line interface when Microsoft first developed it. then he can still see such files. A single user operating system allows only one user at a time. Java. which means its code is available to the public. Operating System Concepts Mrs. A trojan horse appears to be something that it is not so that you give out certain information. Unix can be defeated by Trojan Horses. a version of UNIX developed by Sun Microsystems. This is usually done to the system files such as IO. the Internet. G. Campbell Copyright @ 2010 Updated Jan 2010 119 . There is limited or no security. UNIX UNIX is a multitasking operating system developed at Bell Laboratories. is a multipurpose operating system because it is both a stand-alone and network operating system.g. command-line operating systems developed in the early 1980s for personal computers. You can set attributes on files e. A password is not compulsory on the local computer. Another example is a fake web site on which you give out your credit card information. Example: a fake login screen will allow you to put in your id and password. You can turn off rights/privileges to sub-directories. Linux. is a network O/S designed for ecommerce applications. Hidden etc. You can limit by specific time of day and specific workstations for each user. OS/2 accepts login ID and password and a set of permissions or rights are granted by the LAN administrator. scripting languages and interpreters which are particularly vulnerable to attack because there are so many portals of entry for hackers to exploit.SYS.Case studies Most operating systems use a system of passwords and user ids in order for a user to gain access to the computer and its files. The security is very good but can be vulnerable to attack. Solaris. thereby allowing it to be read by unscrupulous persons. OS/2 OS/2 Warp Client is IBM's GUI multitasking client operating system that supports networking. Later versions used both command-line and menu-driven user interfaces. like UNIX.SYS and MSDOS. and speech recognition. There are a large number of built-in servers. MS-DOS DOS (Disk Operating System) refers to several single user. only on the network. OS/2 Warp Server for e-business is IBM's network O/S designed for business. You can set expiration dates on passwords. Linux is a popular.
providing better performance and a new GUI with a simplified look.g. changing settings). MacOS Mac OS X is a multitasking GUI operating system available only for Apple Macintosh computers. If you still have FAT then you do not have this feature. This O/S uses a secure key chain to manage passwords. If you set a password but the user hits cancel button then the operating system will bring up the default desktop under which you have free reign. user rights. Home edition starts off with administrative privileges and no password by default. There is also secured wireless access. You are able to create multiple user accounts. Templates include password policies. A built-in firewall (called ICF) filters incoming traffic without attempting to manage or restrict outbound connections. It also supports encryption. Windows Server 2003 is an upgrade to Windows 2000 Server and includes features of previous server versions. Windows XP has increased security. Software restrictions . Windows XP Home edition versus Windows XP Professional Windows XP when it came out was Microsoft's fastest. fields. Operating System Concepts Mrs. You are unable to disable simple file sharing in the home edition so be careful on a network if you do not have a firewall. Microsoft Windows Windows 95/98 had limited security. most reliable Windows operating system. If you use NTFS you can set permissions down to the file level.OS/400 This accepts user id and password. service permissions. You may restrict a terminal that a user can use as well as the time that a user may log on to the system. There is also a screen saver password. You are able to group users and set the authority level for the group (user profile). You can set security on admin tasks (e. event log. Windows NT has security holes. records (views). Authority levels can be set on files/objects.You can also prevent certain programs from running (e. account management. The Internet connection firewall protects against hackers. commands. G. There is enhanced system recovery from failure with System Restore feature.g. delete etc. startup modes. policy changes. lockout policies. Blank passwords are not allowed in the Professional edition. The system can force a user to change their password after certain intervals. privilege use and system events. file system permissions. Campbell Copyright @ 2010 Updated Jan 2010 120 . read/write capability. This accepts user id and password. There are also different levels of authority . There are audit logs and audit trails. object access. virus). directories/libraries. It allows directory access control. change. There is also support for biometric devices. NTFS also allows you to encrypt files and folders using the Encrypting Files system (EFS).read only. You can be kicked off the system if you enter an incorrect password 3 times. The professional edition has a Security Configuration Manager (SCM) which allows the administrator to define security templates that can be applied via group policy. There is also auditing which records login. file vault and firewall.
Compare the security features of Windows 7 to previous versions? 3. What are the security features common to most modern operating systems? 2.Windows CE . Pocket PC 2002 is a scaled-down operating system from Microsoft that works on a specific type of PDA. Erase. G. The supervisor may set trustee directory and trustee file assignments. entertainment. Campbell Copyright @ 2010 Updated Jan 2010 121 . There is security at the user level as well as at file and directory levels. The rights that can be set include: Superviros. Modify. You can encrypt communication. and FileScan (sees filenames). There are also inherited rights and file attributes. called the Pocket PC. Netware accepts a userid and password. There is a screen saver password. Read. Discuss the security features of different operating systems. and mobile devices and on handheld computers. Write. Create. Novell Netware NetWare is a network O/S designed for client/server networks. There is also biometric support as well as smart card support. Which operating system do you believe is the most secure? Operating System Concepts Mrs.NET is a scaled-down Windows operating system designed for use on communications. Tutorial Questions 1.
(3rd Ed. G. Gagne. KY:Course Technology Publishing... Prentice Hall: USA.: USA.com. Silberschatz. & Cashman.). 7th E.d. Discovering computers 2008. Modern Operating Systems.B. T.B. Operating Systems Concepts. Andrew S. Galvin. (2004). P. G. Tanenbaum. (2007).J. http://www. John Wiley & Sons Inc. Abraham. Past Operating Systems Concepts examination papers. Campbell Copyright @ 2010 Updated Jan 2010 122 .REFERENCES CCCJ lecturers. Operating System Concepts Mrs.webopedia. Webopedia: Online computer dictionary. Shelly G. Complete Shelly Cashman Series. (2006).
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