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AppleTalk
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AppleTalk over Ethernet
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AppleTalk over Ethernet
As Apple expanded into more commercial and education markets, they needed to integrate AppleTalk into existing network installations. Many of these organisations had already invested in a very expensive Ethernet infrastructure and there was no direct way to connect a Macintosh to Ethernet. AppleTalk included a protocol structure for interconnecting AppleTalk subnets and so as a solution, EtherTalk was initially created to use the Ethernet as a backbone between LocalTalk subnets. To accomplish this, organizations would need to purchase a LocalTalk-to-Ethernet bridge and Apple left it to third parties to produce these products. A number of companies responded, including Hayes and a few newly formed companies like Kinetics.
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AppleTalk
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LocalTalk, EtherTalk, TokenTalk, and AppleShare
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LocalTalk, EtherTalk, TokenTalk, and AppleShare
By 1987, Ethernet was clearly winning the standards battle over Token Ring, and in the middle of that year, Apple introduced EtherTalk 1.0, an implementation of the AppleTalk protocol over the Ethernet physical layer. Introduced for the newly released Macintosh II computer, one of Apple's first two Macintoshes with expansion slots (the Macintosh SE had one slot of a different type), the operating system included a new Network control panel that allowed the user to select which physical connection to use for networking (from "Built-in" or "EtherTalk"). At introduction, Ethernet interface cards were available from 3Com and Kinetics that plugged into a Nubus slot in the machine. The new networking stack also expanded the system to allow a full 255 nodes per LAN. With EtherTalk's release, AppleTalk Personal Network was renamed LocalTalk, the name it would be known under for the bulk of its life. Token Ring would later be supported with a similar TokenTalk product, which used the same Network control panel and underlying software. Over time, many third-party companies would introduce compatible Ethernet and Token Ring cards that used these same drivers.
The appearance of a Macintosh with a direct Ethernet connection also magnified the Ethernet and LocalTalk compatibility problem: Networks with new and old Macs needed some way to communicate with each other. This could be as simple as a network of Ethernet Mac II's trying to talk to a LaserWriter that only connected to LocalTalk. Apple initially relied on the aforementioned LocalTalk-to-Ethernet bridge products, but contrary to Apple's belief that these would be low-volume products, by the end of 1987, 130,000 such networks were in use. AppleTalk was at that time the most used networking system in the world, with over three times the installations of any other vendor.
1987 also marked the introduction of the AppleShare product, a dedicated file server that ran on any Mac with 512 kB of RAM or more. A common AppleShare machine was the Mac Plus with an external SCSI hard drive. AppleShare was the #3 network operating system in the late 1980s, behind Novell NetWare and Microsoft's MS-Net. AppleShare was effectively the replacement for the failed Macintosh Office efforts, which had been based on a dedicated file server device.
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AppleTalk
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AppleTalk Phase II and other developments
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AppleTalk Phase II and other developments
A significant re-design was released in 1989 as AppleTalk Phase II. In many ways, Phase II can be considered an effort to make the earlier version (never called Phase I) more generic. LANs could now support more than 255 nodes, and zones were no longer associated with physical networks but were entirely virtual constructs used simply to organize nodes. For instance, one could now make a "Printers" zone that would list all the printers in an organization, or one might want to place that same device in the "2nd Floor" zone to indicate its physical location. Phase II also included changes to the underlying inter-networking protocols to make them less "chatty", which had previously been a serious problem on networks that bridged over wide-area networks.
By this point, Apple had a wide variety of communications products under development, and many of these were announced along with AppleTalk Phase II. These included updates to EtherTalk and TokenTalk, AppleTalk software and LocalTalk hardware for the IBM PC, EtherTalk for Apple's A/UX operating system allowing it to use LaserWriters and other network resources, and the Mac X.25 and MacX products.
Ethernet had become almost universal by 1990, and it was time to build Ethernet into Macs direct from the factory. However, the physical wiring used by these networks was not yet completely standardized. Apple solved this problem using a single port on the back of the computer into which the user could plug an adaptor for any given cabling system. This FriendlyNet system was based on the industry-standard Attachment Unit Interface or AUI, but deliberately chose a non-standard connector that was smaller and easier to use, which they called "Apple AUI", or AAUI. FriendlyNet was first introduced on the Quadra 700 and Quadra 900 computers, and used across much of the Mac line for some time. As with LocalTalk, a number of third-party FriendlyNet adaptors quickly appeared.
As 10BASE-T became the de facto cabling system for Ethernet, second-generation Power Macintosh machines added a 10BASE-T port in addition to AAUI. The PowerBook 3400c and lower-end Power Macs also added 10BASE-T. The Power Macintosh 7300/8600/9600 were the final Macs to include AAUI, and 10BASE-T became universal starting with the Power Macintosh G3 and PowerBook G3.
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AppleTalk
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The capital-I Internet
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The capital-I Internet
From the beginning of AppleTalk, users wanted to connect the Macintosh to TCP/IP network environments. In 1984, Bill Croft at Stanford University pioneered the development of IP packets encapsulated in DDP as part of the SEAGATE (Stanford Ethernet–AppleTalk Gateway) project. SEAGATE was commercialized by Kinetics in their LocalTalk-to-Ethernet bridge as an additional routing option. A few years later, MacIP was separated from the SEAGATE code and became the de facto method for IP packets to be routed over LocalTalk networks. By 1986, Columbia University released the first version of the Columbia AppleTalk Package (CAP) that allowed higher integration of Unix, TCP/IP, and AppleTalk environments. In 1988, Apple released MacTCP, a system that allowed the Mac to support TCP/IP on machines with suitable Ethernet hardware. However, this left many universities with the problem of supporting IP on their many LocalTalk-equipped Macs. It was soon common to include MacIP support in LocalTalk-to-Ethernet bridges. MacTCP would not become a standard part of the Classic Mac OS until 1994, by which time it also supported SNMP and PPP.
For some time in the early 1990s, the Mac was a primary client on the rapidly expanding Internet. Among the better-known programs in wide use were Fetch, Eudora, eXodus, NewsWatcher, and the NCSA packages, especially NCSA Mosaic and its offspring, Netscape Navigator. Additionally, a number of server products appeared that allowed the Mac to host Internet content. Through this period, Macs had about 2 to 3 times as many clients connected to the Internet as any other platform, despite the relatively small overall microcomputer market share.
As the world quickly moved to IP for both LAN and WAN uses, Apple was faced with maintaining two increasingly outdated code bases on an ever-wider group of machines as well as the introduction of the PowerPC-based machines. This led to the Open Transport efforts, which re-implemented both MacTCP and AppleTalk on an entirely new code base adapted from the Unix standard STREAMS. Early versions had problems and did not become stable for some time. By that point, Apple was deep in their ultimately doomed Copland efforts.
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AppleTalk
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Legacy and abandonment
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Legacy and abandonment
With the purchase of NeXT and subsequent development of Mac OS X, AppleTalk was strictly a legacy system. Support was added to Mac OS X in order to provide support for a large number of existing AppleTalk devices, notably laser printers and file shares, but alternate connection solutions common in this era, notably USB for printers, limited their demand. As Apple abandoned many of these product categories, and all new systems were based on IP, AppleTalk became less and less common. AppleTalk support was finally removed from the macOS line in Mac OS X v10.6 in 2009.
However, the loss of AppleTalk did not reduce the desire for networking solutions that combined its ease of use with IP routing. Apple has led the development of many such efforts, from the introduction of the AirPort router to the development of the zero-configuration networking system and their implementation of it, Rendezvous, later renamed Bonjour.
As of 2020, AppleTalk support has been completely removed from legacy support with macOS 11 Big Sur.
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AppleTalk
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Design
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Design
The AppleTalk design rigorously followed the OSI model of protocol layering. Unlike most of the early LAN systems, AppleTalk was not built using the archetypal Xerox XNS system. The intended target was not Ethernet, and it did not have 48-bit addresses to route. Nevertheless, many portions of the AppleTalk system have direct analogs in XNS.
One key differentiation for AppleTalk was it contained two protocols aimed at making the system completely self-configuring. The AppleTalk address resolution protocol (AARP) allowed AppleTalk hosts to automatically generate their own network addresses, and the Name Binding Protocol (NBP) was a dynamic system for mapping network addresses to user-readable names. Although systems similar to AARP existed in other systems, Banyan VINES for instance. Beginning about 2002 Rendezvous (the combination of DNS-based service discovery, Multicast DNS, and link-local addressing) provided capabilities and usability using IP that were similar to those of AppleTalk.
Both AARP and NBP had defined ways to allow "controller" devices to override the default mechanisms. The concept was to allow routers to provide the information or "hardwire" the system to known addresses and names. On larger networks where AARP could cause problems as new nodes searched for free addresses, the addition of a router could reduce "chattiness." Together AARP and NBP made AppleTalk an easy-to-use networking system. New machines were added to the network by plugging them in and optionally giving them a name. The NBP lists were examined and displayed by a program known as the Chooser which would display a list of machines on the local network, divided into classes such as file-servers and printers.
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AppleTalk
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Addressing
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Addressing
An AppleTalk address was a four-byte quantity. This consisted of a two-byte network number, a one-byte node number, and a one-byte socket number. Of these, only the network number required any configuration, being obtained from a router. Each node dynamically chose its own node number, according to a protocol (originally the LocalTalk Link Access Protocol LLAP and later, for Ethernet/EtherTalk, the AppleTalk Address Resolution Protocol, AARP) which handled contention between different nodes accidentally choosing the same number. For socket numbers, a few well-known numbers were reserved for special purposes specific to the AppleTalk protocol itself. Apart from these, all application-level protocols were expected to use dynamically assigned socket numbers at both the client and server end.
Because of this dynamism, users could not be expected to access services by specifying their address. Instead, all services had names which, being chosen by humans, could be expected to be meaningful to users, and also could be sufficiently long to minimize the chance of conflicts.
As NBP names translated to an address, which included a socket number as well as a node number, a name in AppleTalk mapped directly to a service being provided by a machine, which was entirely separate from the name of the machine itself. Thus, services could be moved to a different machine and, so long as they kept the same service name, there was no need for users to do anything different in order to continue accessing the service. And the same machine could host any number of instances of services of the same type, without any network connection conflicts.
Contrast this with A records in the DNS, in which a name translates to a machine's address, not including the port number that might be providing a service. Thus, if people are accustomed to using a particular machine name to access a particular service, their access will break when the service is moved to a different machine. This can be mitigated somewhat by insistence on using CNAME records indicating service rather than actual machine names to refer to the service, but there is no way of guaranteeing that users will follow such a convention. Some newer protocols, such as Kerberos and Active Directory use DNS SRV records to identify services by name, which is much closer to the AppleTalk model.
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AppleTalk
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Protocols
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Protocols
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AppleTalk
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AppleTalk Address Resolution Protocol
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AppleTalk Address Resolution Protocol
The AppleTalk Address Resolution Protocol (AARP) resolves AppleTalk addresses to link layer addresses. It is functionally equivalent to ARP and obtains address resolution by a method very similar to ARP.
AARP is a fairly simple system. When powered on, an AppleTalk machine broadcasts an AARP probe packet asking for a network address, intending to hear back from controllers such as routers. If no address is provided, one is picked at random from the "base subnet", 0. It then broadcasts another packet saying "I am selecting this address", and then waits to see if anyone else on the network complains. If another machine has that address, the newly connecting machine will pick another address, and keep trying until it finds a free one. On a network with many machines it may take several tries before a free address is found, so for performance purposes the successful address is recorded in NVRAM and used as the default address in the future. This means that in most real-world setups where machines are added a few at a time, only one or two tries are needed before the address effectively becomes constant.
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AppleTalk
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AppleTalk Data Stream Protocol
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AppleTalk Data Stream Protocol
The AppleTalk Data Stream Protocol (ADSP) was a comparatively late addition to the AppleTalk protocol suite, done when it became clear that a TCP-style reliable connection-oriented transport was needed. Significant differences from TCP were that:
A connection attempt could be rejected.
There were no "half-open" connections; once one end initiated a tear-down of the connection, the whole connection would be closed (i.e., ADSP is full-duplex, not dual simplex).
AppleTalk had an included attention message system which allowed short messages to be sent which would bypass the normal stream data flow. These were delivered reliably but out of order with respect to the stream. Any attention message would be delivered as soon as possible instead of waiting for the current stream byte sequence point to become current.
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AppleTalk
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Apple Filing Protocol
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Apple Filing Protocol
The Apple Filing Protocol (AFP), formerly AppleTalk Filing Protocol, is the protocol for communicating with AppleShare file servers. Built on top of AppleTalk Session Protocol (for legacy AFP over DDP) or the Data Stream Interface (for AFP over TCP), it provides services for authenticating users (extensible to different authentication methods including two-way random-number exchange) and for performing operations specific to the Macintosh HFS filesystem. AFP is still in use in macOS, even though most other AppleTalk protocols have been deprecated.
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AppleTalk
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AppleTalk Session Protocol
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AppleTalk Session Protocol
The AppleTalk Session Protocol (ASP) was an intermediate protocol, built on top of AppleTalk Transaction Protocol (ATP), which in turn was the foundation of AFP. It provided basic services for requesting responses to arbitrary commands and performing out-of-band status queries. It also allowed the server to send asynchronous attention messages to the client.
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AppleTalk
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AppleTalk Transaction Protocol
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AppleTalk Transaction Protocol
The AppleTalk Transaction Protocol (ATP) was the original reliable transport-level protocol for AppleTalk, built on top of DDP. At the time it was being developed, a full, reliable connection-oriented protocol like TCP was considered to be too expensive to implement for most of the intended uses of AppleTalk. Thus, ATP was a simple request/response exchange, with no need to set up or tear down connections.
An ATP request packet could be answered by up to eight response packets. The requestor then sent an acknowledgement packet containing a bit mask indicating which of the response packets it received, so the responder could retransmit the remainder.
ATP could operate in either "at-least-once" mode or "exactly-once" mode. Exactly-once mode was essential for operations which were not idempotent; in this mode, the responder kept a copy of the response buffers in memory until successful receipt of a release packet from the requestor, or until a timeout elapsed. This way, it could respond to duplicate requests with the same transaction ID by resending the same response data, without performing the actual operation again.
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AppleTalk
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Datagram Delivery Protocol
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Datagram Delivery Protocol
The Datagram Delivery Protocol (DDP) was the lowest-level data-link-independent transport protocol. It provided a datagram service with no guarantees of delivery. All application-level protocols, including the infrastructure protocols NBP, RTMP and ZIP, were built on top of DDP. AppleTalk's DDP corresponds closely to the Network layer of the Open Systems Interconnection (OSI) communication model.
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AppleTalk
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Name Binding Protocol
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Name Binding Protocol
The Name Binding Protocol (NBP) was a dynamic, distributed system for managing AppleTalk names. When a service started up on a machine, it registered a name for itself as chosen by a human administrator. At this point, NBP provided a system for checking that no other machine had already registered the same name. Later, when a client wanted to access that service, it used NBP to query machines to find that service. NBP provided browsability ("what are the names of all the services available?") as well as the ability to find a service with a particular name. Names were human-readable, containing spaces and upper- and lower-case letters, and including support for searching.
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AppleTalk
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AppleTalk Echo Protocol
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AppleTalk Echo Protocol
The AppleTalk Echo Protocol (AEP) was a transport layer protocol designed to test the reachability of network nodes. AEP generates packets to be sent to the network node and is identified in the Type field of a packet as an AEP packet. The packet is first passed to the source DDP. After it is identified as an AEP packet, it is forwarded to the node where the packet is examined by the DDP at the destination. After the packet is identified as an AEP packet, the packet is then copied and a field in the packet is altered to create an AEP reply packet, and is then returned to the source node.
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AppleTalk
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Printer Access Protocol
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Printer Access Protocol
The Printer Access Protocol (PAP) was the standard way of communicating with PostScript printers. It was built on top of ATP. When a PAP connection was opened, each end sent the other an ATP request which basically meant "send me more data". The client's response to the server was to send a block of PostScript code, while the server could respond with any diagnostic messages that might be generated as a result, after which another "send-more-data" request was sent. This use of ATP provided automatic flow control; each end could only send data to the other end if there was an outstanding ATP request to respond to.
PAP also provided for out-of-band status queries, handled by separate ATP transactions. Even while it was busy servicing a print job from one client, a PAP server could continue to respond to status requests from any number of other clients. This allowed other Macintoshes on the LAN that were waiting to print to display status messages indicating that the printer was busy, and what the job was that it was busy with.
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AppleTalk
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Routing Table Maintenance Protocol
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Routing Table Maintenance Protocol
The Routing Table Maintenance Protocol (RTMP) was the protocol by which routers kept each other informed about the topology of the network. This was the only part of AppleTalk that required periodic unsolicited broadcasts: every 10 seconds, each router had to send out a list of all the network numbers it knew about and how far away it thought they were.
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AppleTalk
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Zone Information Protocol
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Zone Information Protocol
The Zone Information Protocol (ZIP) was the protocol by which AppleTalk network numbers were associated with zone names. A zone was a subdivision of the network that made sense to humans (for example, "Accounting Department"); but while a network number had to be assigned to a topologically contiguous section of the network, a zone could include several different discontiguous portions of the network.
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AppleTalk
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Physical implementation
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Physical implementation
thumb|Farallon PhoneNET adapter
The initial default hardware implementation for AppleTalk was a high-speed serial protocol known as LocalTalk that used the Macintosh's built-in RS-422 ports at 230.4 kbit/s. LocalTalk used a splitter box in the RS-422 port to provide an upstream and downstream cable from a single port. The topology was a bus: cables were daisy-chained from each connected machine to the next, up to the maximum of 32 permitted on any LocalTalk segment. The system was slow by today's standards, but at the time the additional cost and complexity of networking on PC machines was such that it was common that Macs were the only networked personal computers in an office. Other larger computers, such as UNIX or VAX workstations, would commonly be networked via Ethernet.
Other physical implementations were also available. A very popular replacement for LocalTalk was PhoneNET, a third-party solution from Farallon Computing, Inc. (renamed Netopia, acquired by Motorola in 2007) that also used the RS-422 port and was indistinguishable from LocalTalk as far as Apple's LocalTalk port drivers were concerned, but ran over very inexpensive standard phone cabling with four-wire, six-position modular connectors, the same cables used to connect landline telephones. Since it used the second pair of wires, network devices could even be connected through existing telephone jacks if a second line was not present. Foreshadowing today's network hubs and switches, Farallon provided solutions for PhoneNet to be used in star as well as bus configurations, with both passive star connections (with the phone wires simply bridged to each other at a central point), and active star with "PhoneNet Star Controller" hub hardware. In a star configuration, any wiring issue only affected one device, and problems were easy to pinpoint. PhoneNet's low cost, flexibility, and easy troubleshooting resulted in it being the dominant choice for Mac networks into the early 1990s.
AppleTalk protocols also came to run over Ethernet (first coaxial and then twisted pair) and Token Ring physical layers, labeled by Apple as EtherTalk and TokenTalk, respectively. EtherTalk gradually became the dominant implementation method for AppleTalk as Ethernet became generally popular in the PC industry throughout the 1990s. Besides AppleTalk and TCP/IP, any Ethernet network could also simultaneously carry other protocols such as DECnet and IPX.
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AppleTalk
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Networking model
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Networking model
OSI ModelCorresponding AppleTalk layersApplicationApple Filing Protocol (AFP)PresentationApple Filing Protocol (AFP)SessionZone Information Protocol (ZIP)AppleTalk Session Protocol (ASP)AppleTalk Data Stream Protocol (ADSP)TransportAppleTalk Transaction Protocol (ATP)AppleTalk Echo Protocol (AEP)Name Binding Protocol (NBP)Routing Table Maintenance Protocol (RTMP)NetworkDatagram Delivery Protocol (DDP)Data linkEtherTalk Link Access Protocol (ELAP)LocalTalk Link Access Protocol (LLAP) TokenTalk Link Access Protocol (TLAP) Fiber Distributed Data Interface (FDDI)PhysicalLocalTalk driverEthernet driverToken Ring driverFDDI driver
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AppleTalk
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Versions
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Versions
AppleTalk versionApple Filing ProtocolCorresponds toNotes56System 7.057.0.4System 7.1258.1.1System 7.1.258.1.3System 7.560.3Mac OS 7.6.1Open Transport 1.360.0a6Mac OS 8.6 Open Transport 2.0.33.0Mac OS X 10.0.32.1, 2.0 and even 1.1Mac OS X v10.22.2, 3.0 and 3.1Mac OS X v10.33.2Mac OS X v10.4
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AppleTalk
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Cross-platform solutions
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Cross-platform solutions
When AppleTalk was first introduced, the dominant office computing platform was the PC compatible running MS-DOS. Apple introduced the AppleTalk PC Card in early 1987, allowing PCs to join AppleTalk networks and print to LaserWriter printers. A year later AppleShare PC was released, allowing PCs to access AppleShare file servers.
The "TOPS Teleconnector" MS-DOS networking system over AppleTalk system enabled MS-DOS PCs to communicate over AppleTalk network hardware; it comprised an AppleTalk interface card for the PC and a suite of networking software allowing such functions as file, drive and printer sharing. As well as allowing the construction of a PC-only AppleTalk network, it allowed communication between PCs and Macs with TOPS software installed. (Macs without TOPS installed could use the same network but only to communicate with other Apple machines.) The Mac TOPS software did not match the quality of Apple's own either in ease of use or in robustness and freedom from crashes, but the DOS software was relatively simple to use in DOS terms, and was robust.
The BSD and Linux operating systems support AppleTalk through an open source project called Netatalk, which implements the complete protocol suite and allows them to both act as native file or print servers for Macintosh computers, and print to LocalTalk printers over the network.
The Windows Server operating systems supported AppleTalk starting with Windows NT and ending after Windows Server 2003. Miramar included AppleTalk in its PC MacLAN product which was discontinued by CA in 2007. GroupLogic continues to bundle its AppleTalk protocol with its ExtremeZ-IP server software for Macintosh-Windows integration which supports Windows Server 2008 and Windows Vista as well prior versions. HELIOS Software GmbH offers a proprietary implementation of the AppleTalk protocol stack, as part of their HELIOS UB2 server. This is essentially a File and Print Server suite that runs on a whole range of different platforms.
In addition, Columbia University released the Columbia AppleTalk Package (CAP) which implemented the protocol suite for various Unix flavours including Ultrix, SunOS, BSD and IRIX. This package is no longer actively maintained.
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AppleTalk
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See also
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See also
Netatalk is a free, open-source implementation of the AppleTalk suite of protocols.
Network File System
Remote File Sharing
Samba
Server Message Block
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AppleTalk
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Notes
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Notes
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AppleTalk
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References
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References
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AppleTalk
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Citations
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Citations
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AppleTalk
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Bibliography
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Bibliography
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AppleTalk
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External links
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External links
Pushing AppleTalk Across the Internet
Category:Apple Inc. software
Category:Network operating systems
Category:Network protocols
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AppleTalk
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Table of Content
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Short description, History, AppleNet, AppleBus, AppleBus networking, AppleTalk Personal Network, PhoneNet and other adaptors, AppleTalk over Ethernet, LocalTalk, EtherTalk, TokenTalk, and AppleShare, AppleTalk Phase II and other developments, The capital-I Internet, Legacy and abandonment, Design, Addressing, Protocols, AppleTalk Address Resolution Protocol, AppleTalk Data Stream Protocol, Apple Filing Protocol, AppleTalk Session Protocol, AppleTalk Transaction Protocol, Datagram Delivery Protocol, Name Binding Protocol, AppleTalk Echo Protocol, Printer Access Protocol, Routing Table Maintenance Protocol, Zone Information Protocol, Physical implementation, Networking model, Versions, Cross-platform solutions, See also, Notes, References, Citations, Bibliography, External links
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Apple II
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Short description
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Apple II ("apple two", stylized as "Apple ][") is a series of microcomputers manufactured by Apple Computer, Inc. from 1977 to 1993. The original Apple II model, which gave the series its name, was designed by Steve Wozniak and was first sold on June 10, 1977. Its success led to it being followed by the Apple II Plus, Apple IIe, Apple IIc, and Apple IIc Plus, with the 1983 IIe being the most popular. The name is trademarked with square brackets as Apple ][, then, beginning with the IIe, as Apple //.
The Apple II was a major advancement over its predecessor, the Apple I, in terms of ease of use, features, and expandability. It became one of several recognizable and successful computers throughout the 1980s, although this was mainly limited to the US. It was aggressively marketed through volume discounts and manufacturing arrangements to educational institutions, which made it the first computer in widespread use in American secondary schools, displacing the early leader Commodore PET. The effort to develop educational and business software for the Apple II, including the 1979 release of the popular VisiCalc spreadsheet, made the computer especially popular with business users and families.
The Apple II computers are based on the 6502 8-bit processor and can display text and two resolutions of color graphics. A software-controlled speaker provides one channel of low-fidelity audio. A model with more advanced graphics and sound and a 16-bit processor, the Apple IIGS, was added in 1986. It remained compatible with earlier Apple II models, but the IIGS has more in common with mid-1980s systems like the Atari ST, Amiga, and Acorn Archimedes.
Despite the introduction of the Motorola 68000-based Macintosh in 1984, the Apple II series still reportedly accounted for 85% of the company's hardware sales in the first quarter of fiscal 1985. Apple continued to sell Apple II systems alongside the Macintosh until terminating the IIGS in December 1992 and the IIe in November 1993. The last II-series Apple in production, the IIe card for Macintoshes, was discontinued on October 15, 1993; having been one of the longest running mass-produced home computer series, the total Apple II sales of all of its models during its 16-year production run were about 6 million units (including about 1.25 million Apple IIGS models) with the peak occurring in 1983 when 1 million were sold.
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Apple II
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Hardware
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Hardware
thumb|Apple IIe with DuoDisk and Monitor //
Unlike preceding home microcomputers, the Apple II was sold as a finished consumer appliance rather than as a kit (unassembled or preassembled). Apple marketed the Apple II as a durable product, including a 1981 ad in which an Apple II survived a fire started when a cat belonging to one early user knocked over a lamp.
All the machines in the series, except the IIc, share similar overall design elements. The plastic case was designed to look more like a home appliance than a piece of electronic equipment,Helmer, Carl, "An Apple to Byte," Byte, March 1978, p. 18-46. and the case can be opened without the use of tools. All models in the Apple II series have a built-in keyboard, with the exception of the IIGS which has a separate keyboard.
thumb|Apple IIc with monitor
Apple IIs have color and high-resolution graphics modes, sound capabilities and a built-in BASIC programming language. The motherboard holds eight expansion slots and an array of random access memory (RAM) sockets that can hold up to 48 kilobytes. Over the course of the Apple II series' life, an enormous amount of first- and third-party hardware was made available to extend the capabilities of the machine. The IIc was designed as a compact, portable unit, not intended to be disassembled, and cannot use most of the expansion hardware sold for the other machines in the series.
thumb|Apple IIGS
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Apple II
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Software
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Software
The original Apple II has the operating system in ROM along with a BASIC variant called Integer BASIC. Apple eventually released Applesoft BASIC, a more advanced variant of the language which users can run instead of Integer BASIC. The Apple II series eventually supported over 1,500 software programs.
When the Disk II floppy disk drive was released in 1978, a new operating system, Apple DOS, was commissioned from Shepardson Microsystems and developed by Paul Laughton, adding support for the disk drive. The final and most popular version of this software was Apple DOS 3.3.
Apple DOS was superseded by ProDOS, which supported a hierarchical file system and larger storage devices. With an optional third-party Z80-based expansion card, the Apple II could boot into the CP/M operating system and run WordStar, dBase II, and other CP/M software. With the release of MousePaint in 1984 and the Apple IIGS in 1986, the platform took on the look of the Macintosh user interface, including a mouse.
Much commercial Apple II software shipped on self-booting disks and does not use standard DOS disk formats. This discouraged the copying or modifying of the software on the disks, and improved loading speed.
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Apple II
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Models
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Models
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Apple II
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Apple II
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Apple II
thumb|An Apple II computer with an internal modem and external DAA
The first Apple II computers went on sale on June 10, 1977 with a MOS Technology 6502 (later Synertek) microprocessor running at 1.023 MHz, 4 KB of RAM, an audio cassette interface for loading programs and storing data, and the Integer BASIC programming language built into the ROMs. The video controller displayed 40 columns by 24 lines of monochrome, upper-case-only (the original character set matches ASCII characters 0x20 to 0x5F) text on the screen, with NTSC composite video output suitable for display on a TV monitor, or on a regular TV set by way of a separate RF modulator. The original retail price of the computer was (with 4 KB of RAM) and (with the maximum 48 KB of RAM). To reflect the computer's color graphics capability, the Apple logo on the casing was represented using rainbow stripes, which remained a part of Apple's corporate logo until early 1998. The earliest Apple IIs were assembled in Silicon Valley, and later in Texas; printed circuit boards were manufactured in Ireland and Singapore.
An external -inch floppy disk drive, the Disk II, attached via a controller card that plugged into one of the computer's expansion slots (usually slot 6), was used for data storage and retrieval to replace cassettes. The Disk II interface, created by Steve Wozniak, was regarded as an engineering masterpiece for its economy of electronic components.Freiberger, Paul, and Michael Swaine. "Fire In The Valley, Part Two (Book Excerpt)", A+ Magazine, January 1985: 45.
Rather than having a dedicated sound-synthesis chip, the Apple II had a toggle circuit that could only emit a click through a built-in speaker; all other sounds (including two, three and, eventually, four-voice music and playback of audio samples and speech synthesis) were generated entirely by software that clicked the speaker at just the right times.
The Apple II's multiple expansion slots permitted a wide variety of third-party devices, including Apple II peripheral cards such as serial controllers, display controllers, memory boards, hard disks, networking components, and real-time clocks. There were plug-in expansion cards – such as the Z-80 SoftCard – that permitted the Apple to use the Z80 processor and run a multitude of programs developed under the CP/M operating system, including the dBase II database and the WordStar word processor. There was also a third-party 6809 card that would allow OS-9 Level One to be run. Third-party sound cards greatly improved audio capabilities, allowing simple music synthesis and text-to-speech functions. Eventually, Apple II accelerator cards were created to double or quadruple the computer's speed.
Rod Holt designed the Apple II's power supply. He employed a switched-mode power supply design, which was far smaller and generated less unwanted heat than the linear power supply some other home computers used.
The original Apple II was discontinued at the start of 1981; it was superseded by the Apple II+.
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Apple II
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Apple II Plus
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Apple II Plus
thumb|Apple II Plus
The Apple II Plus, introduced in June 1979, included the Applesoft BASIC programming language in ROM. This Microsoft-authored dialect of BASIC, which was previously available as an upgrade, supported floating-point arithmetic, and became the standard BASIC dialect on the Apple II series (though it ran at a noticeably slower speed than Steve Wozniak's Integer BASIC).
Except for improved graphics and disk-booting support in the ROM, and the removal of the 2k 6502 assembler to make room for the floating point BASIC, the II+ was otherwise identical to the original II in terms of electronic functionality. There were small differences in the physical appearance and keyboard. RAM prices fell during 1980–81 and all II+ machines came from the factory with a full 48 KB of memory already installed.
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Apple II
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Apple II Europlus and J-Plus
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Apple II Europlus and J-Plus
thumb|Apple II Europlus
thumb|Apple II J-Plus
After the success of the first Apple II in the United States, Apple expanded its market to include Europe, the Middle East, Australia and the Far East in 1979, with the Apple II Europlus (Europe, Australia) and the Apple II J-Plus (Japan). In these models, Apple made the necessary hardware, software and firmware changes in order to comply to standards outside of the US.
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Apple II
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Apple IIe
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Apple IIe
The Apple II Plus was followed in 1983 by the Apple IIe, a cost-reduced yet more powerful machine that used newer chips to reduce the component count and add new features, such as the display of upper and lowercase letters and a standard 64 KB of RAM.
The IIe RAM was configured as if it were a 48 KB Apple II Plus with a language card. The machine had no slot 0, but instead had an auxiliary slot that could accept a 1 KB memory card to enable the 80-column display. This card contained only RAM; the hardware and firmware for the 80-column display was built into the Apple IIe. An "extended 80-column card" with more memory increased the machine's RAM to 128 KB.
The Apple IIe was the most popular machine in the Apple II series. It has the distinction of being the longest-lived Apple computer of all time—it was manufactured and sold with only minor changes for nearly 11 years. The IIe was the last Apple II model to be sold, and was discontinued in November 1993.
During its lifespan two variations were introduced: the Apple IIe Enhanced (four replacement chips to give it some of the features of the later model Apple IIc) and the Apple IIe Platinum (a modernized case color to match other Apple products of the era, along with the addition of a numeric keypad).
Some of the feature of the IIe were carried over from the less successful Apple III, among them the ProDOS operating system.
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Apple II
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Apple IIc
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Apple IIc
thumb|The Apple IIc was Apple's first compact and portable computer.
The Apple IIc was released in April 1984, billed as a portable Apple II because it could be easily carried due to its size and carrying handle, which could be flipped down to prop the machine up into a typing position. Unlike modern portables, it lacked a built-in display and battery. It was the first of three Apple II models to be made in the Snow White design language, and the only one that used its unique creamy off-white color."Kunkel, Paul, AppleDesign: The work of the Apple Industrial Design Group, with photographs by Rick English, New York: Graphis, 1997, p.30
The Apple IIc was the first Apple II to use the 65C02 low-power variant of the 6502 processor, and featured a built-in 5.25-inch floppy drive and 128 KB RAM, with a built-in disk controller that could control external drives, composite video (NTSC or PAL), serial interfaces for modem and printer, and a port usable by either a joystick or mouse. Unlike previous Apple II models, the IIc had no internal expansion slots at all.
Two different monochrome LC displays were sold for use with the IIc's video expansion port, although both were short-lived due to high cost and poor legibility. The IIc had an external power supply that converted AC power to 15 V DC, though the IIc itself will accept between 12 V and 17 V DC, allowing third parties to offer battery packs and automobile power adapters that connected in place of the supplied AC adapter.
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Apple II
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Apple II<small>GS</small>
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Apple IIGS
thumb|Apple IIGS with monitor, keyboard, mouse, joystick, 3.5" floppy disk drive and 5.25" floppy disk drive
The Apple IIGS, released on September 15, 1986, is the penultimate and most advanced model in the Apple II series, and a radical departure from prior models. It uses a 16-bit microprocessor, the 65C816 operating at 2.8 MHz with 24-bit addressing, allowing expansion up to 8 MB of RAM. The graphics are significantly improved, with 4096 colors and new modes with resolutions of 320×200 and 640×400.Duprau, Jeanne, and Tyson, Molly. "The Making of the Apple IIGS", A+ Magazine, November 1986: 57–74. The audio capabilities are vastly improved, with a built-in music synthesizer that far exceeded any other home computer.
The Apple IIGS evolved the platform while still maintaining near-complete backward compatibility. Its Mega II chip contains the functional equivalent of an entire Apple IIe computer (sans processor). This, combined with the 65816's ability to execute 65C02 code directly, provides full support for legacy software, while also supporting 16-bit software running under a new OS.
The OS eventually included a Macintosh-like graphical Finder for managing disks and files and opening documents and applications, along with desk accessories. Later, the IIGS gained the ability to read and write Macintosh disks and, through third-party software, a multitasking Unix-like shell and TrueType font support.
The GS includes a 32-voice Ensoniq 5503 DOC sample-based sound synthesizer chip with 64 KB dedicated RAM, 256 KB (or later 1.125 MB) of standard RAM, built-in peripheral ports (switchable between IIe-style card slots and IIc-style onboard controllers for disk drives, mouse, RGB video, and serial devices), and built-in AppleTalk networking.
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Apple II
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Apple IIc Plus
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Apple IIc Plus
thumb|The Apple IIc Plus, an enhancement of the original portable with faster CPU, 3.5-inch floppy, and built-in power supply. It was the last model in the Apple II line.
The final Apple II model was the Apple IIc Plus introduced in 1988. It was the same size and shape as the IIc that came before it, but the 5.25-inch floppy drive had been replaced with a -inch drive, the power supply was moved inside the case, and the processor was a fast 4 MHz 65C02 processor that actually ran 8-bit Apple II software faster than the IIGS.
The IIc Plus also featured a new keyboard layout that matched the Platinum IIe and IIGS. Unlike the IIe IIc and IIGS, the IIc Plus came only in one version (American) and was not officially sold anywhere outside the US. The Apple IIc Plus ceased production in 1990, with its two-year production run being the shortest of all the Apple II computers.
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Apple II
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Apple IIe Card
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Apple IIe Card
Although not an extension of the Apple II line, in 1990 the Apple IIe Card, an expansion card for the Macintosh LC, was released. Essentially a miniaturized Apple IIe computer on a card (using the Mega II chip from the Apple IIGS), it allowed the Macintosh to run 8-bit Apple IIe software through hardware emulation, with an option to run at roughly double the speed of the original IIe (about 1.8 MHz). However, the video output was emulated in software, and, depending on how much of the screen the currently running program was trying to update in a single frame, performance could be much slower compared to a real IIe. This is due to the fact that writes from the 65C02 on the IIe Card to video memory were caught by the additional hardware on the card, so the video emulation software running on the Macintosh side could process that write and update the video display. But, while the Macintosh was processing video updates, execution of Apple II code would be temporarily halted.
With a breakout cable which connected to the back of the card, the user could attach up to two UniDisk or Apple 5.25 Drives, up to one UniDisk 3.5 drive, and a DE-9 Apple II joystick. Many of the LC's built-in Macintosh peripherals could also be "borrowed" by the card when in Apple II mode, including extra RAM, the Mac's internal 3.5-inch floppy drives, AppleTalk networking, any ProDOS-formatted hard disk partitions, the serial ports, mouse, and real-time clock. The IIe card could not, however, run software intended for the 16-bit Apple IIGS.
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Apple II
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Advertising, marketing, and packaging
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Advertising, marketing, and packaging
thumb|A 1977 Byte magazine advertisement for the original Apple II
Mike Markkula, a retired Intel marketing manager, provided the early critical funding for Apple Computer. From 1977 to 1981, Apple used the Regis McKenna agency for its advertisements and marketing. In 1981, Chiat-Day acquired Regis McKenna's advertising operations and Apple used Chiat-Day. At Regis McKenna Advertising, the team assigned to launch the Apple II consisted of Rob Janoff, art director, Chip Schafer, copywriter and Bill Kelley, account executive. Janoff came up with the Apple logo with a bite out of it. The design was originally an olive green with matching company logotype all in lowercase. Steve Jobs insisted on promoting the color capability of the Apple II by putting rainbow stripes on the Apple logo. In its letterhead and business card implementation, the rounded "a" of the logotype echoed the "bite" in the logo. This logo was developed simultaneously with an advertisement and a brochure; the latter being produced for distribution initially at the first West Coast Computer Faire.
Since the original Apple II, Apple has paid high attention to its quality of packaging, partly because of Steve Jobs' personal preferences and opinions on packaging and final product appearance.Moritz, Michael. The Little Kingdom. New York, William Morrow and Company, Inc, 1984: pg. 186. All of Apple's packaging for the Apple II series looked similar, featuring much clean white space and showing the Apple rainbow logo prominently.A gallery of Apple IIGS packaging from DigiBarn For several years up until the late 1980s, Apple used the Motter Tektura font for packaging, until changing to the Apple Garamond font.
Apple ran the first advertisement for the Apple II, a two-page spread ad titled "Introducing Apple II", in BYTE in July 1977. The first brochure, was entitled "Simplicity" and the copy in both the ad and brochure pioneered "demystifying" language intended to make the new idea of a home computer more "personal." The Apple II introduction ad was later run in the September 1977 issue of Scientific American.
Apple later aired eight television commercials for the Apple IIGS, emphasizing its benefits to education and students, along with some print ads.
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Apple II
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Clones
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Clones
The Apple II was frequently cloned, both in the United States and abroad, in a similar way to the IBM PC. According to some sources (see below), more than 190 different models of Apple II clones were manufactured. Most could not be legally imported into the United States. Apple sued and sought criminal charges against clone makers in more than a dozen countries.
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Apple II
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Data storage
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Data storage
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Apple II
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Cassette
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Cassette
Originally the Apple II used Compact Cassette tapes for program and data storage. A dedicated tape recorder along the lines of the Commodore Datasette was never produced; Apple recommended using the Panasonic RQ309 in some of its early printed documentation. The uses of common consumer cassette recorders and a standard video monitor or television set (with a third-party RF modulator) made the total cost of owning an Apple II less expensive and helped contribute to the Apple II's success.
Cassette storage may have been inexpensive, but it was also slow and unreliable. The Apple II's lack of a disk drive was "a glaring weakness" in what was otherwise intended to be a polished, professional product. Recognizing that the II needed a disk drive to be taken seriously, Apple set out to develop a disk drive and a DOS to run it. Wozniak spent the 1977 Christmas holidays designing a disk controller that reduced the number of chips used by a factor of 10 compared to existing controllers. Still lacking a DOS, and with Wozniak inexperienced in operating system design, Jobs approached Shepardson Microsystems with the project. On April 10, 1978, Apple signed a contract for $13,000 with Shepardson to develop the DOS.
Even after disk drives made the cassette tape interfaces obsolete they were still used by enthusiasts as simple one-bit audio input-output ports. Ham radio operators used the cassette input to receive slow scan TV (single frame images). A commercial speech recognition Blackjack program was available, after some user-specific voice training it would recognize simple commands (Hit, stand). Bob Bishop's "Music Kaleidoscope" was a simple program that monitored the cassette input port and based on zero-crossings created color patterns on the screen, a predecessor to current audio visualization plug-ins for media players. Music Kaleidoscope was especially popular on projection TV sets in dance halls.
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Apple II
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The OS Disk
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The OS Disk
Apple and many third-party developers made software available on tape at first, but after the Disk II became available in 1978, tape-based Apple II software essentially disappeared from the market. The initial price of the Disk II drive and controller was US$595, although a $100 off coupon was available through the Apple newsletter "Contact". The controller could handle two drives and a second drive (without controller) retailed for $495.
The Disk II single-sided floppy drive used 5.25-inch floppy disks; double-sided disks could be used, one side at a time, by turning them over and notching a hole for the write protect sensor. The first disk operating systems for the were and DOS 3.2, which stored 113.75 KB on each disk, organized into 35 tracks of 13 256-byte sectors each. After about two years, DOS 3.3 was introduced, storing 140 KB thanks to a minor firmware change on the disk controller that allowed it to store 16 sectors per track. (This upgrade was user-installable as two PROMs on older controllers.) After the release of DOS 3.3, the user community discontinued use of except for running legacy software. Programs that required DOS 3.2 were fairly rare; however, as DOS 3.3 was not a major architectural change aside from the number of sectors per track, a program called MUFFIN was provided with DOS 3.3 to allow users to copy files from DOS 3.2 disks to DOS 3.3 disks. It was possible for software developers to create a DOS 3.2 disk which would also boot on a system with firmware.
Later, double-sided drives, with heads to read both sides of the disk, became available from third-party companies. (Apple only produced double-sided 5.25-inch disks for the Lisa 1 computer).
On a DOS 3.x disk, tracks 0, 1, and most of track 2 were reserved to store the operating system. (It was possible, with a special utility, to reclaim most of this space for data if a disk did not need to be bootable.) A short ROM program on the disk controller had the ability to seek to track zero which it did without regard for the read/write head's current position, resulting in the characteristic "chattering" sound of a Disk II boot, which was the read/write head hitting the rubber stop block at the end of the rail – and read and execute code from sector 0. The code contained in there would then pull in the rest of the operating system. DOS stored the disk's directory on track 17, smack in the middle of the 35-track disks, in order to reduce the average seek time to the frequently used directory track. The directory was fixed in size and could hold a maximum of 105 files. Subdirectories were not supported.
Most game publishers did not include DOS on their floppy disks, since they needed the memory it occupied more than its capabilities; instead, they often wrote their own boot loaders and read-only file systems. This also served to discourage "crackers" from snooping around in the game's copy-protection code, since the data on the disk was not in files that could be accessed easily.
Some third-party manufacturers produced floppy drives that could write 40 tracks to most 5.25-inch disks, yielding 160 KB of storage per disk, but the format did not catch on widely, and no known commercial software was published on 40-track media. Most drives, even Disk IIs, could write 36 tracks; a two byte modification to DOS to format the extra track was common.
The Apple Disk II stored 140 KB on single-sided, "single-density" floppy disks, but it was very common for Apple II users to extend the capacity of a single-sided floppy disk to 280 KB by cutting out a second write-protect notch on the side of the disk using a "disk notcher" or hole puncher and inserting the disk flipped over. Double-sided disks, with notches on both sides, were available at a higher price, but in practice the magnetic coating on the reverse of nominally single-sided disks was usually of good enough quality to be used (both sides were coated in the same way to prevent warping, although only one side was certified for use). Early on, diskette manufacturers routinely warned that this technique would damage the read/write head of the drives or wear out the disk faster, and these warnings were frequently repeated in magazines of the day. In practice, however, this method was an inexpensive way to store twice as much data for no extra cost, and was widely used for commercially released floppies as well.
Later, Apple IIs were able to use 3.5-inch disks with a total capacity of 800 KB and hard disks. did not support these drives natively; third-party software was required, and disks larger than about 400 KB had to be split up into multiple "virtual disk volumes."
DOS 3.3 was succeeded by ProDOS, a 1983 descendant of the Apple ///'s SOS. It added support for subdirectories and volumes up to 32 MB in size. ProDOS became the DOS of choice; AppleWorks and other newer programs required it.
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Apple II
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Legacy
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Legacy
thumb|Apple II Europlus computer with Scandinavian keyboard layout in Helsinki's computer and game console museum
The Apple II series of computers had an enormous impact on the technology industry and expanded the role of microcomputers in society. The Apple II was the first personal computer many people ever saw. Its price was within the reach of many middle-class families, and a partnership with MECC helped make the Apple II popular in schools. By the end of 1980 Apple had already sold over 100,000 Apple IIs, and at the introduction of the IIGS, models in the range had been sold. However, in other markets, the range saw rather more limited adoption, with only 120,000 units selling in the UK over this nine-year period.
The Apple II's popularity bootstrapped the computer game and educational software markets and began the boom in the word processor and computer printer markets. The first spreadsheet application, VisiCalc, was initially released for the Apple II, and many businesses bought them just to run VisiCalc. Its success drove IBM in part to create the IBM PC, which many businesses purchased to run spreadsheet and word processing software, at first ported from Apple II versions.
The Apple II's slots, allowing any peripheral card to take control of the bus and directly access memory, enabled an independent industry of card manufacturers who together created a flood of hardware products that let users build systems that were far more powerful and useful (at a lower cost) than any competing system, most of which were not nearly as expandable and were universally proprietary. The first peripheral card was a blank prototyping card intended for electronics enthusiasts who wanted to design their own peripherals for the Apple II.
Specialty peripherals kept the Apple II in use in industry and education environments for many years after Apple Computer stopped supporting the Apple II. Well into the 1990s every clean-room (the super-clean facility where spacecraft are prepared for flight) at the Kennedy Space Center used an Apple II to monitor the environment and air quality. Most planetariums used Apple IIs to control their projectors and other equipment.
Even the game port was unusually powerful and could be used for digital and analog input and output. The early manuals included instructions for how to build a circuit with only four commonly available components (one transistor and three resistors) and a software routine to drive a common Teletype Model 33 machine. Don Lancaster used the game port I/O to drive a LaserWriter printer.
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Apple II
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Modern use
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Modern use
Today, emulators for various Apple II models are available to run Apple II software on macOS, Linux, Microsoft Windows, homebrew enabled Nintendo DS and other operating systems. Numerous disk images of Apple II software are available free over the Internet for use with these emulators. AppleWin and MESS are among the best emulators compatible with most Apple II images. The MESS emulator supports recording and playing back of Apple II emulation sessions, as does Home Action Replay Page (a.k.a. HARP).
There is still a small annual convention, KansasFest, dedicated to the platform.
In 2017, the band 8 Bit Weapon released the world's first 100% Apple II-based music album entitled, "Class Apples". The album featured dance-oriented cover versions of classical music by Bach, Beethoven, and Mozart recorded directly off the Apple II motherboard.
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Apple II
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See also
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See also
Apple Industrial Design Group
List of publications and periodicals devoted to the Apple II
Apple II peripheral cards
Apple II graphics
List of Apple II application software
List of Apple II games
List of Apple IIGS games
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Apple II
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References
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References
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Apple II
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External links
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External links
epocalc Apple II clones list
"These Pictures Of Apple's First Employees Are Absolutely Wonderful", contains a c.1977 photograph taken inside Apple of early employees Chrisann Brennan, Mark Johnson, and Robert Martinengo standing in front of a stack of Apple IIs that they had tested, assembled, and were about to ship (Business Insider, December 26, 2013).
Apple II computers
Category:Computer-related introductions in 1977
Category:Products and services discontinued in 1993
Category:Discontinued Apple Inc. products
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Apple II
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Table of Content
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Short description, Hardware, Software, Models, Apple II, Apple II Plus, Apple II Europlus and J-Plus, Apple IIe, Apple IIc, Apple II<small>GS</small>, Apple IIc Plus, Apple IIe Card, Advertising, marketing, and packaging, Clones, Data storage, Cassette, The OS Disk, Legacy, Modern use, See also, References, External links
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Apple III
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Short description
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The Apple III (styled as apple ///) is a business-oriented personal computer produced by Apple Computer and released in 1980. Running the Apple SOS operating system, it was intended as the successor to the Apple II; however, it was largely considered a failure in the market. It was designed to provide features business users wanted: a true typewriter-style keyboard with upper and lowercase letters (the Apple II only supported uppercase at the time) and an 80-column display.
It had the internal code name of "Sara", named after Wendell Sander's daughter. The system was announced on May 19, 1980, and released in late November that year. Serious stability issues required a design overhaul and a recall of the first 14,000 machines produced. The Apple III was formally reintroduced on November 9, 1981.
Damage to the computer's reputation had already been done, however, and it failed to do well commercially. Development stopped, and the Apple III was discontinued on April 24, 1984. Its last successor, the III Plus, was dropped from the Apple product line in September 1985.
An estimated 65,000 to 75,000 Apple III computers were sold. The Apple III Plus brought this up to approximately 120,000. Apple co-founder Steve Wozniak stated that the primary reason for the Apple III's failure was that the system was designed by Apple's marketing department, unlike Apple's previous engineering-driven projects. The Apple III's failure led Apple to reevaluate its plan to phase out the Apple II, prompting the eventual continuation of development of the older machine. As a result, later Apple II models incorporated some hardware and software technologies of the Apple III.
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Apple III
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Overview
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Overview
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Apple III
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Design
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Design
Steve Wozniak and Steve Jobs expected hobbyists to purchase the Apple II; however, because of VisiCalc and Disk II, small businesses purchased 90% of the computers. The Apple III was designed to be a business computer and successor. Though the Apple II contributed to the inspirations of several important business products, such as VisiCalc, Multiplan, and Apple Writer, the computer's hardware architecture, operating system, and developer environment are limited. Apple management intended to clearly establish market segmentation by designing the Apple III to appeal to the 90% business market, leaving the Apple II to home and education users. Management believed that "once the Apple III was out, the Apple II would stop selling in six months", Wozniak said.
The Apple III is powered by a 2 megahertz Synertek 6502A or 6502B 8-bit CPU (operating effectively between 1.4 and 1.8 MHz due to video or memory refresh cycles) and, like some of the later machines in the Apple II family, uses bank switching techniques to address memory beyond the 6502's traditional 64 KB limit, up to 256 KB in the III's case. Third-party vendors produced memory upgrade kits that allow the Apple III to reach up to 512 KB of random-access memory (RAM). Other Apple III built-in features include an 80-column, 24-line display with upper and lowercase characters, a numeric keypad, dual-speed (pressure-sensitive) cursor control keys, 6-bit (DAC) audio, and a built-in 140-kilobyte 5.25-inch floppy disk drive. Graphics modes include 560x192 in black and white, and 280x192 with 16 colors or shades of gray. Unlike the Apple II, the Disk III controller is part of the logic board.
The Apple III is the first Apple product to allow the user to choose both a screen font and a keyboard layout: either QWERTY or Dvorak. These choices cannot be changed while programs were running. This was unlike the Apple IIc, which has a keyboard switch directly above the keyboard, allowing the user to switch on the fly.
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Apple III
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Software
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Software
thumb|An advertisement for access to health information through the Apple III
The Apple III introduced an advanced operating system called Apple SOS, pronounced "apple sauce". Its ability to address resources by name allows the Apple III to be more scalable than the Apple II's addressing by physical location such as PR#6 and CATALOG, D1. Apple SOS allows the full capacity of a storage device to be used as a single volume, such as the Apple ProFile hard disk drive, and it supports a hierarchical file system. Some of the features and code base of Apple SOS were later adopted into the Apple II's ProDOS and GS/OS operating systems, as well as Lisa 7/7 and Mac OS.
With a starting price of $4,340 (equivalent to $17,356 as of 2024) and a maximum price of $7,800 (equivalent to $31,194 as of 2024), the Apple III was more expensive than many of the CP/M-based business computers that were available at the time. Few software applications other than VisiCalc are available for the computer; according to a presentation at KansasFest 2012, fewer than 50 Apple III-specific software packages were ever published, most shipping when the III Plus was released. However this number is proven to be wildly incorrect, given the manual 'RESOURCE GUIDE: Of Apple /// and Apple /// Plus Software and Hardware' published and released by Apple Computer, Inc. in May 1984 lists in excess of 500+ software packages produced by many and varied publishers. Given software publishers and specialised hardware manufacturers such as On-Three, Inc. produced products for the Apple III well in to the late 90s, in excess of 500 products can also be seen as way too conservative.
Because Apple did not view the Apple III as suitable for hobbyists, it did not provide much of the technical software information that accompanies the Apple II. Originally intended as a direct replacement to the Apple II, it was designed to be backward compatible with Apple II software. However, since Apple did not want to encourage continued development of the II platform, Apple II compatibility exists only in a special Apple II Mode which is limited in its capabilities to the emulation of a basic Apple II Plus configuration with of RAM.
Special chips were intentionally added to prevent access from Apple II Mode to the III's advanced features such as its larger amount of memory.
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Apple III
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Peripherals
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Peripherals
The Apple III has four expansion slots, a number that inCider in 1986 called "miserly"., also saying Apple II cards are compatible but risk violating government RFI regulations, and require Apple III-specific device drivers; BYTE stated that "Apple provides virtually no information on how to write them". As with software, Apple provided little hardware technical information with the computer but Apple III-specific products became available, such as one that made the computer compatible with the Apple IIe. Several new Apple-produced peripherals were developed for the Apple III. The original Apple III has a built-in real-time clock, which is recognized by Apple SOS. The clock was later removed from the "revised" model, and was instead made available as an add-on.
Along with the built-in floppy drive, the Apple III can also handle up to three additional external Disk III floppy disk drives. The Disk III is only officially compatible with the Apple III. The Apple III Plus requires an adaptor from Apple to use the Disk III with its DB-25 disk port.
With the introduction of the revised Apple III a year after launch, Apple began offering the ProFile external hard disk system. Priced at $3,499 for 5 MB of storage, it also required a peripheral slot for its controller card.
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Apple III
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Backward compatibility
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Backward compatibility
The Apple III has the built-in hardware capability to run Apple II software. In order to do so, an emulation boot disk is required that functionally turns the machine into a standard 48-kilobyte Apple II Plus, until it is powered off. The keyboard, internal floppy drive (and one external Disk III), display (color is provided through the 'B/W video' port) and speaker all act as Apple II peripherals. The paddle and serial ports can also function in Apple II mode, however with some limitations and compatibility issues.
Apple engineers added specialized circuitry with the sole purpose of blocking access to its advanced features when running in Apple II emulation mode. This was done primarily to discourage further development and interest in the Apple II line, and to push the Apple III as its successor. For example, no more than of RAM can be accessed, even if the machine has of RAM or higher present. Many Apple II programs require a minimum of of RAM, making them impossible to run on the Apple III. Similarly, access to lowercase support, 80 columns text, or its more advanced graphics and sound are blocked by this hardware circuitry, making it impossible for even skilled software programmers to bypass Apple's lockout. A third-party company, Titan Technologies, sold an expansion board called the III Plus II that allows Apple II mode to access more memory, a standard game port, and with a later released companion card, even emulate the Apple IIe.
Certain Apple II slot cards can be installed in the Apple III and used in native III-mode with custom written SOS device drivers, including Grappler Plus and Liron 3.5 Controller.
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Apple III
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Revisions
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Revisions
thumb|Apple III Plus
After overheating issues were attributed to serious design flaws, a redesigned logic board was introduced in mid-December 1981 – which included a lower power supply requirement, wider circuit traces and better-designed chip sockets. The $3,495 revised model also includes 256 KB of RAM as the standard configuration. The 14,000 units of the original Apple III sold were returned and replaced with the entirely new revised model.
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Apple III
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Apple III Plus
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Apple III Plus
Apple discontinued the III in October 1983 because it violated FCC regulations, and the FCC required the company to change the redesigned computer's name. It introduced the Apple III Plus in December 1983 at a price of US$2,995. This newer version includes a built-in clock, video interlacing, standardized rear port connectors, 55-watt power supply, 256 KB of RAM as standard, and a redesigned, Apple IIe-like keyboard.
Owners of the Apple III could purchase individual III Plus upgrades, like the clock and interlacing feature, and obtain the newer logic board as a service replacement. A keyboard upgrade kit, dubbed "Apple III Plus upgrade kit" was also made available – which included the keyboard, cover, keyboard encoder ROM, and logo replacements. This upgrade had to be installed by an authorized service technician.
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Apple III
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Design flaws
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Design flaws
According to Wozniak, the Apple III "had 100 percent hardware failures". Former Apple executive Taylor Pohlman stated that:
Jobs insisted on the idea of having no fan or air vents, in order to make the computer run quietly. He would later push this same ideology onto almost all Apple models he had control of, from the Apple Lisa and Macintosh 128K to the iMac. To allow the computer to dissipate heat, the base of the Apple III was made of heavy cast aluminum, which supposedly acts as a heat sink. One advantage to the aluminum case was a reduction in RFI (Radio Frequency Interference), a problem which had plagued the Apple II series throughout its history. Unlike the Apple II, the power supply was mounted – without its own shell – in a compartment separate from the logic board. The decision to use an aluminum shell ultimately led to engineering issues which resulted in the Apple III's reliability problems. The lead time for manufacturing the shells was high, and this had to be done before the motherboard was finalized. Later, it was realized that there was not enough room on the motherboard for all of the components unless narrow traces were used.
thumb|Apple III Plus showing the RFI shield over the floppy drive and the cast aluminum case
Many Apple IIIs were thought to have failed due to their inability to properly dissipate heat. inCider stated in 1986 that "Heat has always been a formidable enemy of the Apple ///", and some users reported that their Apple IIIs became so hot that the chips started dislodging from the board, causing the screen to display garbled data or their disk to come out of the slot "melted". BYTE wrote, "the integrated circuits tended to wander out of their sockets". It has been rumored Apple advised customers to tilt the front of the Apple III six inches above the desk and then drop it to reseat the chips as a temporary solution. Other analyses blame a faulty automatic chip insertion process, not heat.
Case designer Jerry Manock denied the design flaw charges, insisting that tests proved that the unit adequately dissipated the internal heat. The primary cause, he claimed, was a major logic board design problem. The logic board used "fineline" technology that was not fully mature at the time, with narrow, closely spaced traces. When chips were "stuffed" into the board and wave-soldered, solder bridges would form between traces that were not supposed to be connected. This caused numerous short circuits, which required hours of costly diagnosis and hand rework to fix. Apple designed a new circuit board with more layers and normal-width traces. The new logic board was laid out by one designer on a huge drafting board, rather than using the costly CAD-CAM system used for the previous board, and the new design worked.
Earlier Apple III units came with a built-in real time clock. The hardware, however, would fail after prolonged use. Assuming that National Semiconductor would test all parts before shipping them, Apple did not perform this level of testing. Apple was soldering chips directly to boards and could not easily replace a bad chip if one was found. Eventually, Apple solved this problem by removing the real-time clock from the Apple III's specification rather than shipping the Apple III with the clock pre-installed, and then sold the peripheral as a level 1 technician add-on.
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Apple III
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BASIC
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BASIC
Microsoft and Apple each developed their own versions of BASIC for the Apple III. Apple III Microsoft BASIC was designed to run on the CP/M platform available for the Apple III. Apple Business BASIC shipped with the Apple III. Donn Denman ported Applesoft BASIC to SOS and reworked it to take advantage of the extended memory of the Apple III.
Both languages introduced a number of new or improved features over Applesoft BASIC. Both languages replaced Applesoft's single-precision floating-point variables using 5-byte storage with the somewhat-reduced-precision 4-byte variables, while also adding a larger numerical format. Apple III Microsoft BASIC provides double-precision floating-point variables, taking 8 bytes of storage,Apple III Microsoft BASIC Reference Manual, Microsoft Corporation, 1982 while Apple Business BASIC offers an extra-long integer type, also taking 8 bytes for storage.Apple Business BASIC Reference Manual, Apple Computer, Inc., 1981 Both languages also retain 2-byte integers, and maximum 255-character strings.
Other new features common to both languages include:
Incorporation of disk-file commands within the language.
Operators for MOD and for integer-division.
An optional ELSE clause in IF...THEN statements.
HEX$() function for hexadecimal-format output.
INSTR function for finding a substring within a string.
PRINT USING statement to control format of output. Apple Business BASIC had an option, in addition to directly specifying the format with a string expression, of giving the line number where an IMAGE statement gave the formatting expression, similar to a FORMAT statement in FORTRAN.
Some features work differently in each language:
Apple III Microsoft BASIC Apple Business BASIC integer division operator \ (backslash) DIV reading the keyboard without waiting INKEY$ function returns a one-character string representing the last key pressed, or the null string if no new key pressed since last reading KBD read-only "reserved variable" returns the ASCII code of the last key pressed; the manual fails to document what is returned if no new key pressed since last reading reassigning a portion of a string variable MID$() assignment statement SUB$() assignment statement determining position of text output POS() function to read horizontal screen position, and LPOS() function to read horizontal position on printer HPOS and VPOS assignable "reserved variables" to read or set the horizontal or vertical position for text screen output accepting hexadecimal-format values "&H"-formatted expressions TEN() function to give numerical value from string representing hexadecimal result of ASC("")
(null string operand) causes an error returns the value −1
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Apple III
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Microsoft BASIC additional features
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Microsoft BASIC additional features
function to replace Applesoft's command.
statement to input an entire line of text, regardless of punctuation, into a single string variable.
and statements to automatically direct output to paper.
and statements to left- or right-justify a string expression within a given string variable's character length.
function for output, and "&"- or "&O"-formatted expressions, for manipulating octal notation.
function for generating blank spaces outside of a statement, and function to do likewise with any character.
... statements, for loop structures built on general Boolean conditions without an index variable.
Bitwise Boolean (16-bit) operations (, , ), with additional operators , , .
Line number specification in the command.
options of (to skip to the statement after that which caused the error) or a specified line number (which replaces the idea of exiting error-handling by -line, thus avoiding Applesoft II's stack error problem).
Multiple parameters in user-defined () functions.
A return to the old Applesoft One concept of having multiple functions at different addresses, by establishing ten different functions, numbered to , with separate statements to define the address of each. The argument passed to a function can be of any specific type, including string. The returned value can also be of any type, by default the same type as the argument passed.
There is no support for graphics provided within the language, nor for reading analog controls or buttons; nor is there a means of defining the active window of the text screen.
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Apple III
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Business BASIC additional features
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Business BASIC additional features
Apple Business BASIC eliminates all references to absolute memory addresses. Thus, the POKE command and PEEK() function were not included in the language, and new features replaced the CALL statement and USR() function. The functionality of certain features in Applesoft that had been achieved with various PEEK and POKE locations is now provided by:
BUTTON() function to read game-controller buttons
WINDOW statement to define the active window of the text screen by its coordinates
KBD, HPOS, and VPOS system variables
External binary subroutines and functions are loaded into memory by a single INVOKE disk-command that loads separately-assembled code modules. A PERFORM statement is then used to call an INVOKEd procedure by name, with an argument-list. INVOKEd functions would be referenced in expressions by EXFN. (floating-point) or EXFN%. (integer), with the function name appended, plus the argument-list for the function.
Graphics are supported with an INVOKEd module, with features including displaying text within graphics in various fonts, within four different graphics modes available on the Apple III.
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Apple III
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Reception
|
Reception
"The Apple III is unlikely to approach the success of the Apple II", InfoWorld said in January 1981. Citing the III's high price, manufacturing delays, limited disk storage, and small software library, the magazine asked "why buy a $5000 computer with an emulator when most of the programs you need run directly on a $2500 computer".
Despite devoting the majority of its R&D to the Apple III and so ignoring the II that for a while dealers had difficulty in obtaining the latter, the III's technical problems made marketing the computer difficult. Ed Smith, who after designing the APF Imagination Machine worked as a distributor's representative, described the III as "a complete disaster". He recalled that he "was responsible for going to every dealership, setting up the Apple III in their showroom, and then explaining to them the functions of the Apple III, which in many cases didn't really work".
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Apple III
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Sales
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Sales
BYTE reported in 1982 that Apple had sold only 10,000 of the original Apple III, compared to 350,000 Apple IIs sold by the end of 1981. Pohlman reported that Apple was only selling 500 units a month by late 1981, mostly as replacements. The company was able to eventually raise monthly sales to 5,000, but the IBM PC's successful launch had encouraged software companies to develop for it instead, prompting Apple to shift focus to the Lisa and Macintosh. The PC almost ended sales of the Apple III, the most closely comparable Apple computer model. By early 1984, sales were primarily to existing III owners, Apple itself—its 4,500 employees were equipped with some 3,000-4,500 units—and some small businesses. Apple finally discontinued the Apple III series on April 24, 1984, four months after introducing the III Plus, after selling only up to 75,000 units and replacing 14,000 defective units.
Jobs said the company lost "incalculable amounts" of money on the Apple III. Wozniak estimated that Apple had spent $100 million on the III instead of improving the II and better competing against IBM. Pohlman claimed that there was a "stigma" at Apple associated with having contributed to the computer. Most employees who worked on the III reportedly left Apple.
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Apple III
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Legacy
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Legacy
The file system and some design ideas from Apple SOS, the Apple III's operating system, were part of Apple ProDOS and Apple GS/OS, the major operating systems for the Apple II following the demise of the Apple III, as well as the Apple Lisa, which was the de facto business-oriented successor to the Apple III. The hierarchical file system influenced the evolution of the Macintosh: while the original Macintosh File System (MFS) was a flat file system designed for a floppy disk without subdirectories, subsequent file systems were hierarchical. By comparison, the IBM PC's first file system (again designed for floppy disks) was also flat and later versions (designed for hard disks) were hierarchical.
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Apple III
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In popular culture
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In popular culture
At the start of the Walt Disney Pictures film Tron, lead character Kevin Flynn (played by Jeff Bridges) is seen hacking into the ENCOM mainframe using an Apple III.
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Apple III
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References
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References
Sources
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Apple III
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External links
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External links
The Ill-Fated Apple III
Many manuals and diagrams
Sara – Apple /// emulator
The Ill-Fated Apple III Low End Mac
Apple III Chaos: Apple's First Failure Low End Mac
Category:Apple II family
Category:Computer-related introductions in 1980
Category:Products and services discontinued in 1984
Category:Discontinued Apple Inc. products
Category:8-bit computers
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Apple III
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Table of Content
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Short description, Overview, Design, Software, Peripherals, Backward compatibility, Revisions, Apple III Plus, Design flaws, BASIC, Microsoft BASIC additional features, Business BASIC additional features, Reception, Sales, Legacy, In popular culture, References, External links
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AVL tree
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Short description
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thumb|Animation showing the insertion of several elements into an AVL tree. It includes left, right, left-right and right-left rotations.
thumb|right|262px|Fig. 1: AVL tree with balance factors (green)
In computer science, an AVL tree (named after inventors Adelson-Velsky and Landis) is a self-balancing binary search tree. In an AVL tree, the heights of the two child subtrees of any node differ by at most one; if at any time they differ by more than one, rebalancing is done to restore this property. Lookup, insertion, and deletion all take time in both the average and worst cases, where is the number of nodes in the tree prior to the operation. Insertions and deletions may require the tree to be rebalanced by one or more tree rotations.
The AVL tree is named after its two Soviet inventors, Georgy Adelson-Velsky and Evgenii Landis, who published it in their 1962 paper "An algorithm for the organization of information". English translation by Myron J. Ricci in Soviet Mathematics - Doklady, 3:1259–1263, 1962. It is the first self-balancing binary search tree data structure to be invented.
AVL trees are often compared with red–black trees because both support the same set of operations and take time for the basic operations. For lookup-intensive applications, AVL trees are faster than red–black trees because they are more strictly balanced. Similar to red–black trees, AVL trees are height-balanced. Both are, in general, neither weight-balanced nor -balanced for any ;AVL trees are not weight-balanced? (meaning: AVL trees are not μ-balanced?) Thereby: A Binary Tree is called -balanced, with , if for every node , the inequality
holds and is minimal with this property. is the number of nodes below the tree with as root (including the root) and is the left child node of . that is, sibling nodes can have hugely differing numbers of descendants.
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AVL tree
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Definition
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Definition
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AVL tree
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Balance factor
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Balance factor
In a binary tree the balance factor of a node X is defined to be the height difference
of its two child sub-trees rooted by node X.
A node X with is called "left-heavy", one with is called "right-heavy", and one with is sometimes simply called "balanced".
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AVL tree
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Properties
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Properties
Balance factors can be kept up-to-date by knowing the previous balance factors and the change in height – it is not necessary to know the absolute height. For holding the AVL balance information, two bits per node are sufficient.However, the balance information can be kept in the child nodes as one bit indicating whether the parent is higher by 1 or by 2; thereby higher by 2 cannot occur for both children. This way the AVL tree is a "rank balanced" tree, as coined by Haeupler, Sen and Tarjan.
The height (counted as the maximal number of levels) of an AVL tree with nodes lies in the interval:
where is the golden ratio and
This is because an AVL tree of height contains at least nodes where is the Fibonacci sequence with the seed values
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AVL tree
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Operations
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Operations
Read-only operations of an AVL tree involve carrying out the same actions as would be carried out on an unbalanced binary search tree, but modifications have to observe and restore the height balance of the sub-trees.
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AVL tree
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Searching
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Searching
Searching for a specific key in an AVL tree can be done the same way as that of any balanced or unbalanced binary search tree. In order for search to work effectively it has to employ a comparison function which establishes a total order (or at least a total preorder) on the set of keys. The number of comparisons required for successful search is limited by the height and for unsuccessful search is very close to , so both are in .
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AVL tree
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Traversal
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Traversal
As a read-only operation the traversal of an AVL tree functions the same way as on any other binary tree. Exploring all nodes of the tree visits each link exactly twice: one downward visit to enter the subtree rooted by that node, another visit upward to leave that node's subtree after having explored it.
Once a node has been found in an AVL tree, the next or previous node can be accessed in amortized constant time. Some instances of exploring these "nearby" nodes require traversing up to links (particularly when navigating from the rightmost leaf of the root's left subtree to the root or from the root to the leftmost leaf of the root's right subtree; in the AVL tree of figure 1, navigating from node P to the next-to-the-right node Q takes 3 steps). Since there are links in any tree, the amortized cost is , or approximately 2.
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AVL tree
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Insert
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Insert
When inserting a node into an AVL tree, you initially follow the same process as inserting into a Binary Search Tree. If the tree is empty, then the node is inserted as the root of the tree. If the tree is not empty, then we go down the root, and recursively go down the tree searching for the location to insert the new node. This traversal is guided by the comparison function. In this case, the node always replaces a NULL reference (left or right) of an external node in the tree i.e., the node is either made a left-child or a right-child of the external node.
After this insertion, if a tree becomes unbalanced, only ancestors of the newly inserted node are unbalanced. This is because only those nodes have their sub-trees altered. So it is necessary to check each of the node's ancestors for consistency with the invariants of AVL trees: this is called "retracing". This is achieved by considering the balance factor of each node.
Since with a single insertion the height of an AVL subtree cannot increase by more than one, the temporary balance factor of a node after an insertion will be in the range For each node checked, if the temporary balance factor remains in the range from –1 to +1 then only an update of the balance factor and no rotation is necessary. However, if the temporary balance factor is ±2, the subtree rooted at this node is AVL unbalanced, and a rotation is needed. With insertion as the code below shows, the adequate rotation immediately perfectly rebalances the tree.
In figure 1, by inserting the new node Z as a child of node X the height of that subtree Z increases from 0 to 1.
Invariant of the retracing loop for an insertion
The height of the subtree rooted by Z has increased by 1. It is already in AVL shape.
for (X = parent(Z); X != null; X = parent(Z)) { // Loop (possibly up to the root)
// BF(X) has to be updated:
if (Z == right_child(X)) { // The right subtree increases
if (BF(X) > 0) { // X is right-heavy
// ==> the temporary BF(X) == +2
// ==> rebalancing is required.
G = parent(X); // Save parent of X around rotations
if (BF(Z) < 0) // Right Left Case (see figure 3)
N = rotate_RightLeft(X, Z); // Double rotation: Right(Z) then Left(X)
else // Right Right Case (see figure 2)
N = rotate_Left(X, Z); // Single rotation Left(X)
// After rotation adapt parent link
} else {
if (BF(X) < 0) {
BF(X) = 0; // Z’s height increase is absorbed at X.
break; // Leave the loop
}
BF(X) = +1;
Z = X; // Height(Z) increases by 1
continue;
}
} else { // Z == left_child(X): the left subtree increases
if (BF(X) < 0) { // X is left-heavy
// ==> the temporary BF(X) == -2
// ==> rebalancing is required.
G = parent(X); // Save parent of X around rotations
if (BF(Z) > 0) // Left Right Case
N = rotate_LeftRight(X, Z); // Double rotation: Left(Z) then Right(X)
else // Left Left Case
N = rotate_Right(X, Z); // Single rotation Right(X)
// After rotation adapt parent link
} else {
if (BF(X) > 0) {
BF(X) = 0; // Z’s height increase is absorbed at X.
break; // Leave the loop
}
BF(X) = -1;
Z = X; // Height(Z) increases by 1
continue;
}
}
// After a rotation adapt parent link:
// N is the new root of the rotated subtree
// Height does not change: Height(N) == old Height(X)
parent(N) = G;
if (G != null) {
if (X == left_child(G))
left_child(G) = N;
else
right_child(G) = N;
} else
tree->root = N; // N is the new root of the total tree
break;
// There is no fall thru, only break; or continue;
}
// Unless loop is left via break, the height of the total tree increases by 1.
In order to update the balance factors of all nodes, first observe that all nodes requiring correction lie from child to parent along the path of the inserted leaf. If the above procedure is applied to nodes along this path, starting from the leaf, then every node in the tree will again have a balance factor of −1, 0, or 1.
The retracing can stop if the balance factor becomes 0 implying that the height of that subtree remains unchanged.
If the balance factor becomes ±1 then the height of the subtree increases by one and the retracing needs to continue.
If the balance factor temporarily becomes ±2, this has to be repaired by an appropriate rotation after which the subtree has the same height as before (and its root the balance factor 0).
The time required is for lookup, plus a maximum of retracing levels ( on average) on the way back to the root, so the operation can be completed in time.
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AVL tree
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Delete
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Delete
The preliminary steps for deleting a node are described in section Binary search tree#Deletion.
There, the effective deletion of the subject node or the replacement node decreases the height of the corresponding child tree either from 1 to 0 or from 2 to 1, if that node had a child.
Starting at this subtree, it is necessary to check each of the ancestors for consistency with the invariants of AVL trees. This is called "retracing".
Since with a single deletion the height of an AVL subtree cannot decrease by more than one, the temporary balance factor of a node will be in the range from −2 to +2.
If the balance factor remains in the range from −1 to +1 it can be adjusted in accord with the AVL rules. If it becomes ±2 then the subtree is unbalanced and needs to be rotated. (Unlike insertion where a rotation always balances the tree, after delete, there may be BF(Z) ≠ 0 (see figures 2 and 3), so that after the appropriate single or double rotation the height of the rebalanced subtree decreases by one meaning that the tree has to be rebalanced again on the next higher level.) The various cases of rotations are described in section Rebalancing.
Invariant of the retracing loop for a deletion
The height of the subtree rooted by N has decreased by 1. It is already in AVL shape.
for (X = parent(N); X != null; X = G) { // Loop (possibly up to the root)
G = parent(X); // Save parent of X around rotations
// BF(X) has not yet been updated!
if (N == left_child(X)) { // the left subtree decreases
if (BF(X) > 0) { // X is right-heavy
// ==> the temporary BF(X) == +2
// ==> rebalancing is required.
Z = right_child(X); // Sibling of N (higher by 2)
b = BF(Z);
if (b < 0) // Right Left Case (see figure 3)
N = rotate_RightLeft(X, Z); // Double rotation: Right(Z) then Left(X)
else // Right Right Case (see figure 2)
N = rotate_Left(X, Z); // Single rotation Left(X)
// After rotation adapt parent link
} else {
if (BF(X) == 0) {
BF(X) = +1; // N’s height decrease is absorbed at X.
break; // Leave the loop
}
N = X;
BF(N) = 0; // Height(N) decreases by 1
continue;
}
} else { // (N == right_child(X)): The right subtree decreases
if (BF(X) < 0) { // X is left-heavy
// ==> the temporary BF(X) == -2
// ==> rebalancing is required.
Z = left_child(X); // Sibling of N (higher by 2)
b = BF(Z);
if (b > 0) // Left Right Case
N = rotate_LeftRight(X, Z); // Double rotation: Left(Z) then Right(X)
else // Left Left Case
N = rotate_Right(X, Z); // Single rotation Right(X)
// After rotation adapt parent link
} else {
if (BF(X) == 0) {
BF(X) = -1; // N’s height decrease is absorbed at X.
break; // Leave the loop
}
N = X;
BF(N) = 0; // Height(N) decreases by 1
continue;
}
}
// After a rotation adapt parent link:
// N is the new root of the rotated subtree
parent(N) = G;
if (G != null) {
if (X == left_child(G))
left_child(G) = N;
else
right_child(G) = N;
} else
tree->root = N; // N is the new root of the total tree
if (b == 0)
break; // Height does not change: Leave the loop
// Height(N) decreases by 1 (== old Height(X)-1)
}
// If (b != 0) the height of the total tree decreases by 1.
The retracing can stop if the balance factor becomes ±1 (it must have been 0) meaning that the height of that subtree remains unchanged.
If the balance factor becomes 0 (it must have been ±1) then the height of the subtree decreases by one and the retracing needs to continue.
If the balance factor temporarily becomes ±2, this has to be repaired by an appropriate rotation. It depends on the balance factor of the sibling Z (the higher child tree in figure 2) whether the height of the subtree decreases by one –and the retracing needs to continue– or does not change (if Z has the balance factor 0) and the whole tree is in AVL-shape.
The time required is for lookup, plus a maximum of retracing levels ( on average) on the way back to the root, so the operation can be completed in time.
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AVL tree
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Set operations and bulk operations
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Set operations and bulk operations
In addition to the single-element insert, delete and lookup operations, several set operations have been defined on AVL trees: union, intersection and set difference. Then fast bulk operations on insertions or deletions can be implemented based on these set functions. These set operations rely on two helper operations, Split and Join. With the new operations, the implementation of AVL trees can be more efficient and highly-parallelizable..
The function Join on two AVL trees and and a key will return a tree containing all elements in , as well as . It requires to be greater than all keys in and smaller than all keys in . If the two trees differ by height at most one, Join simply create a new node with left subtree , root and right subtree . Otherwise, suppose that is higher than for more than one (the other case is symmetric). Join follows the right spine of until a node which is balanced with . At this point a new node with left child , root and right child is created to replace c. The new node satisfies the AVL invariant, and its height is one greater than . The increase in height can increase the height of its ancestors, possibly invalidating the AVL invariant of those nodes. This can be fixed either with a double rotation if invalid at the parent or a single left rotation if invalid higher in the tree, in both cases restoring the height for any further ancestor nodes. Join will therefore require at most two rotations. The cost of this function is the difference of the heights between the two input trees.
function JoinRightAVL(TL, k, TR)
(l, k', c) = expose(TL)
if (Height(c) <= Height(TR)+1)
T' = Node(c, k, TR)
if (Height(T') <= Height(l)+1) then return Node(l, k', T')
else return rotateLeft(Node(l, k', rotateRight(T')))
else
T' = JoinRightAVL(c, k, TR)
T'' = Node(l, k', T')
if (Height(T') <= Height(l)+1) return T''
else return rotateLeft(T'')
function JoinLeftAVL(TL, k, TR)
/* symmetric to JoinRightAVL */
function Join(TL, k, TR)
if (Height(TL)>Height(TR)+1) return JoinRightAVL(TL, k, TR)
if (Height(TR)>Height(TL)+1) return JoinLeftAVL(TL, k, TR)
return Node(TL, k, TR)
Here Height(v) is the height of a subtree (node) . (l,k,r) = expose(v) extracts 's left child , the key of 's root, and the right child . Node(l,k,r) means to create a node of left child , key , and right child .
To split an AVL tree into two smaller trees, those smaller than key , and those greater than key , first draw a path from the root by inserting into the AVL. After this insertion, all values less than will be found on the left of the path, and all values greater than will be found on the right. By applying Join, all the subtrees on the left side are merged bottom-up using keys on the path as intermediate nodes from bottom to top to form the left tree, and the right part is asymmetric. The cost of Split is , order of the height of the tree.
function Split(T, k)
if (T = nil) return (nil, false, nil)
(L,m,R) = expose(T)
if (k = m) return (L, true, R)
if (k<m)
(L',b,R') = Split(L,k)
return (L', b, Join(R', m, R))
if (k>m)
(L',b,R') = Split(R, k)
return (Join(L, m, L'), b, R'))
The union of two AVL trees and representing sets and , is an AVL that represents .
function Union(t1, t2):
if t1 = nil:
return t2
if t2 = nil:
return t1
(t<, b, t>) = Split(t2, t1.root)
return Join(Union(left(t1), t<), t1.root, Union(right(t1), t>))
Here, Split is presumed to return two trees: one holding the keys less its input key, one holding the greater keys. (The algorithm is non-destructive, but an in-place destructive version exists as well.)
The algorithm for intersection or difference is similar, but requires the Join2 helper routine that is the same as Join but without the middle key. Based on the new functions for union, intersection or difference, either one key or multiple keys can be inserted to or deleted from the AVL tree. Since Split calls Join but does not deal with the balancing criteria of AVL trees directly, such an implementation is usually called the "join-based" implementation.
The complexity of each of union, intersection and difference is for AVL trees of sizes and . More importantly, since the recursive calls to union, intersection or difference are independent of each other, they can be executed in parallel with a parallel depth . When , the join-based implementation has the same computational DAG as single-element insertion and deletion.
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AVL tree
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Rebalancing
|
Rebalancing
If during a modifying operation the height difference between two child subtrees changes, this may, as long as it is < 2, be reflected by an adaption of the balance information at the parent. During insert and delete operations a (temporary) height difference of 2 may arise, which means that the parent subtree has to be "rebalanced". The given repair tools are the so-called tree rotations, because they move the keys only "vertically", so that the ("horizontal") in-order sequence of the keys is fully preserved (which is essential for a binary-search tree).
Let X be the node that has a (temporary) balance factor of −2 or +2. Its left or right subtree was modified. Let Z be the child with the higher subtree (see figures 2 and 3). Note that both children are in AVL shape by induction hypothesis.
In case of insertion this insertion has happened to one of Z's children in a way that Z's height has increased.
In case of deletion this deletion has happened to the sibling t1 of Z in a way so that t1's height being already lower has decreased. (This is the only case where Z's balance factor may also be 0.)
There are four possible variants of the violation:
Right Right ⟹ Z is a right child of its parent X and BF(Z) ≥ 0 Left Left ⟹ Z is a left child of its parent X and BF(Z) ≤ 0 Right Left ⟹ Z is a right child of its parent X and BF(Z) < 0 Left Right ⟹ Z is a left child of its parent X and BF(Z) > 0
And the rebalancing is performed differently:
Right Right ⟹ X is rebalanced with a simple rotation rotate_Left (see figure 2) Left Left ⟹ X is rebalanced with a simple rotation rotate_Right (mirror-image of figure 2) Right Left ⟹ X is rebalanced with a double rotation rotate_RightLeft (see figure 3) Left Right ⟹ X is rebalanced with a double rotation rotate_LeftRight (mirror-image of figure 3)
Thereby, the situations are denoted as where C (= child direction) and B (= balance) come from the set } with The balance violation of case is repaired by a simple rotation whereas the case is repaired by a double rotation
The cost of a rotation, either simple or double, is constant.
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AVL tree
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Simple rotation
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Simple rotation
Figure 2 shows a Right Right situation. In its upper half, node X has two child trees with a balance factor of +2. Moreover, the inner child t23 of Z (i.e., left child when Z is right child, or right child when Z is left child) is not higher than its sibling t4. This can happen by a height increase of subtree t4 or by a height decrease of subtree t1. In the latter case, also the pale situation where t23 has the same height as t4 may occur.
The result of the left rotation is shown in the lower half of the figure. Three links (thick edges in figure 2) and two balance factors are to be updated.
As the figure shows, before an insertion, the leaf layer was at level h+1, temporarily at level h+2 and after the rotation again at level h+1. In case of a deletion, the leaf layer was at level h+2, where it is again, when t23 and t4 were of same height. Otherwise the leaf layer reaches level h+1, so that the height of the rotated tree decreases.
thumb|right|194px|Fig. 2: Simple rotationrotate_Left(X,Z)
Code snippet of a simple left rotation
Input: X = root of subtree to be rotated left Z = right child of X, Z is right-heavy with height == XResult: new root of rebalanced subtree
node *rotate_Left(node *X, node *Z) {
// Z is by 2 higher than its sibling
t23 = left_child(Z); // Inner child of Z
right_child(X) = t23;
if (t23 != null)
parent(t23) = X;
left_child(Z) = X;
parent(X) = Z;
// 1st case, BF(Z) == 0,
// only happens with deletion, not insertion:
if (BF(Z) == 0) { // t23 has been of same height as t4
BF(X) = +1; // t23 now higher
BF(Z) = –1; // t4 now lower than X
} else
{ // 2nd case happens with insertion or deletion:
BF(X) = 0;
BF(Z) = 0;
}
return Z; // return new root of rotated subtree
}
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AVL tree
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Double rotation
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Double rotation
Figure 3 shows a Right Left situation. In its upper third, node X has two child trees with a balance factor of +2. But unlike figure 2, the inner child Y of Z is higher than its sibling t4. This can happen by the insertion of Y itself or a height increase of one of its subtrees t2 or t3 (with the consequence that they are of different height) or by a height decrease of subtree t1. In the latter case, it may also occur that t2 and t3 are of the same height.
The result of the first, the right, rotation is shown in the middle third of the figure. (With respect to the balance factors, this rotation is not of the same kind as the other AVL single rotations, because the height difference between Y and t4 is only 1.) The result of the final left rotation is shown in the lower third of the figure. Five links (thick edges in figure 3) and three balance factors are to be updated.
As the figure shows, before an insertion, the leaf layer was at level h+1, temporarily at level h+2 and after the double rotation again at level h+1. In case of a deletion, the leaf layer was at level h+2 and after the double rotation it is at level h+1, so that the height of the rotated tree decreases.
thumb|right|264px|Fig. 3: Double rotation rotate_RightLeft(X,Z)= rotate_Right around Z followed byrotate_Left around X
Code snippet of a right-left double rotation
Input: X = root of subtree to be rotated Z = its right child, left-heavy with height == XResult: new root of rebalanced subtree
node *rotate_RightLeft(node *X, node *Z) {
// Z is by 2 higher than its sibling
Y = left_child(Z); // Inner child of Z
// Y is by 1 higher than sibling
t3 = right_child(Y);
left_child(Z) = t3;
if (t3 != null)
parent(t3) = Z;
right_child(Y) = Z;
parent(Z) = Y;
t2 = left_child(Y);
right_child(X) = t2;
if (t2 != null)
parent(t2) = X;
left_child(Y) = X;
parent(X) = Y;
// 1st case, BF(Y) == 0
if (BF(Y) == 0) {
BF(X) = 0;
BF(Z) = 0;
} else if (BF(Y) > 0) {
// t3 was higher
BF(X) = –1; // t1 now higher
BF(Z) = 0;
} else {
// t2 was higher
BF(X) = 0;
BF(Z) = +1; // t4 now higher
}
BF(Y) = 0;
return Y; // return new root of rotated subtree
}
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AVL tree
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Comparison to other structures
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Comparison to other structures
Both AVL trees and red–black (RB) trees are self-balancing binary search trees and they are related mathematically. Indeed, every AVL tree can be colored red–black, but there are RB trees which are not AVL balanced. For maintaining the AVL (or RB) tree's invariants, rotations play an important role. In the worst case, even without rotations, AVL or RB insertions or deletions require inspections and/or updates to AVL balance factors (or RB colors). RB insertions and deletions and AVL insertions require from zero to three tail-recursive rotations and run in amortized time, thus equally constant on average. AVL deletions requiring rotations in the worst case are also on average. RB trees require storing one bit of information (the color) in each node, while AVL trees mostly use two bits for the balance factor, although, when stored at the children, one bit with meaning «lower than sibling» suffices. The bigger difference between the two data structures is their height limit.
For a tree of size
an AVL tree's height is at most
where the golden ratio, and .
a RB tree's height is at most
.Red–black tree#Proof of bounds
AVL trees are more rigidly balanced than RB trees with an asymptotic relation AVL/RB ≈0.720 of the maximal heights. For insertions and deletions, Ben Pfaff shows in 79 measurements a relation of AVL/RB between 0.677 and 1.077 with median ≈0.947 and geometric mean ≈0.910.
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AVL tree
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See also
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See also
WAVL tree
Weight-balanced tree
Splay tree
Scapegoat tree
B-tree
T-tree
List of data structures
|
AVL tree
|
References
|
References
|
AVL tree
|
Further reading
|
Further reading
Donald Knuth. The Art of Computer Programming, Volume 3: Sorting and Searching, Third Edition. Addison-Wesley, 1997. . Pages 458–475 of section 6.2.3: Balanced Trees.
.
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AVL tree
|
External links
|
External links
Category:1962 in computing
Category:Articles with example pseudocode
Category:Binary trees
Category:Soviet inventions
Category:Search trees
Category:Amortized data structures
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AVL tree
|
Table of Content
|
Short description, Definition, Balance factor, Properties, Operations, Searching, Traversal, Insert, Delete, Set operations and bulk operations, Rebalancing, Simple rotation, Double rotation, Comparison to other structures, See also, References, Further reading, External links
|
Aliphatic compound
|
Short description
|
thumb|right|220px|Acyclic aliphatic/non-aromatic compound (butane) thumb|right|170px|Cyclic aliphatic/non-aromatic compound (cyclobutane)
In organic chemistry, hydrocarbons (compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. aleiphar, fat, oil). Aliphatic compounds can be saturated (in which all the C-C bonds are single, requiring the structure to be completed, or 'saturated', by hydrogen) like hexane, or unsaturated, like hexene and hexyne. Open-chain compounds, whether straight or branched, and which contain no rings of any type, are always aliphatic. Cyclic compounds can be aliphatic if they are not aromatic.
|
Aliphatic compound
|
Structure
|
Structure
Aliphatics compounds can be saturated, joined by single bonds (alkanes), or unsaturated, with double bonds (alkenes) or triple bonds (alkynes). If other elements (heteroatoms) are bound to the carbon chain, the most common being oxygen, nitrogen, sulfur, and chlorine, it is no longer a hydrocarbon, and therefore no longer an aliphatic compound. However, such compounds may still be referred to as aliphatic if the hydrocarbon portion of the molecule is aliphatic, e.g. aliphatic amines, to differentiate them from aromatic amines.
The least complex aliphatic compound is methane (CH4).
|
Aliphatic compound
|
Properties
|
Properties
Most aliphatic compounds are flammable, allowing the use of hydrocarbons as fuel, such as methane in natural gas for stoves or heating; butane in torches and lighters; various aliphatic (as well as aromatic) hydrocarbons in liquid transportation fuels like petrol/gasoline, diesel, and jet fuel; and other uses such as ethyne (acetylene) in welding.
|
Aliphatic compound
|
Examples of aliphatic compounds
|
Examples of aliphatic compounds
The most important aliphatic compounds are:
n-, iso- and cyclo-alkanes (saturated hydrocarbons)
n-, iso- and cyclo-alkenes and -alkynes (unsaturated hydrocarbons).
Important examples of low-molecular aliphatic compounds can be found in the list below (sorted by the number of carbon-atoms):
Formula Name Structural formula Chemical classification Methane 75px Alkane Acetylene 75px Alkyne Ethylene 75px Alkene Ethane 75px Alkane Propyne 75px Alkyne Propene 100px Alkene Propane 100px Alkane 1,2-Butadiene 100px Diene 1-Butyne 100px Alkyne 1-Butene 65px Alkene Butane 100px Alkane Cyclohexene 40px Cycloalkene n-pentane 75px Alkane Cycloheptane 50px Cycloalkane Methylcyclohexane 75px Cyclohexane Cubane 75px Prismane, Platonic hydrocarbon Nonane 100px Alkane Dicyclopentadiene 125px Diene, Cycloalkene Phellandrene 50px50px Terpene, Diene, Cycloalkene α-Terpinene 90px Terpene, Diene, Cycloalkene Limonene 50px50px Terpene, Diene, Cycloalkene Undecane 125px Alkane Squalene 125px Terpene, Polyene Polyethylene 75px Alkane
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Aliphatic compound
|
References
|
References
Category:Organic compounds
|
Aliphatic compound
|
Table of Content
|
Short description, Structure, Properties, Examples of aliphatic compounds, References
|
Astrology
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short description
|
Astrology is a range of divinatory practices, recognized as pseudoscientific since the 18th century, that propose that information about human affairs and terrestrial events may be discerned by studying the apparent positions of celestial objects. Different cultures have employed forms of astrology since at least the 2nd millennium BCE, these practices having originated in calendrical systems used to predict seasonal shifts and to interpret celestial cycles as signs of divine communications.
Most, if not all, cultures have attached importance to what they observed in the sky, and some—such as the Hindus, Chinese, and the Maya—developed elaborate systems for predicting terrestrial events from celestial observations. Western astrology, one of the oldest astrological systems still in use, can trace its roots to 19th–17th century BCE Mesopotamia, from where it spread to Ancient Greece, Rome, the Islamic world, and eventually Central and Western Europe. Contemporary Western astrology is often associated with systems of horoscopes that purport to explain aspects of a person's personality and predict significant events in their lives based on the positions of celestial objects; the majority of professional astrologers rely on such systems.
Throughout its history, astrology has had its detractors, competitors and skeptics who opposed it for moral, religious, political, and empirical reasons. Nonetheless, prior to the Enlightenment, astrology was generally considered a scholarly tradition and was common in learned circles, often in close relation with astronomy, meteorology, medicine, and alchemy. It was present in political circles and is mentioned in various works of literature, from Dante Alighieri and Geoffrey Chaucer to William Shakespeare, Lope de Vega, and Pedro Calderón de la Barca. During the Enlightenment, however, astrology lost its status as an area of legitimate scholarly pursuit.
Following the end of the 19th century and the wide-scale adoption of the scientific method, researchers have successfully challenged astrology on both theoretical and experimental grounds, and have shown it to have no scientific validity or explanatory power. Astrology thus lost its academic and theoretical standing in the western world, and common belief in it largely declined, until a continuing resurgence starting in the 1960s.
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Astrology
|
Etymology
|
Etymology
thumb|upright|right|Marcantonio Raimondi engraving, 15th century
The word astrology comes from the early Latin word astrologia, which derives from the Greek —from ἄστρον astron ("star") and -λογία -logia, ("study of"—"account of the stars"). The word entered the English language via Latin and medieval French, and its use overlapped considerably with that of astronomy (derived from the Latin astronomia). By the 17th century, astronomy became established as the scientific term, with astrology referring to divinations and schemes for predicting human affairs.
|
Astrology
|
History
|
History
thumb|upright|The Zodiac Man, a diagram of a human body and astrological symbols with instructions explaining the importance of astrology from a medical perspective. From a 15th-century Welsh manuscript
Many cultures have attached importance to astronomical events, and the Indians, Chinese, and Maya developed elaborate systems for predicting terrestrial events from celestial observations. A form of astrology was practised in the Old Babylonian period of Mesopotamia, . Vedāṅga Jyotiṣa is one of earliest known Hindu texts on astronomy and astrology (Jyotisha). The text is dated between 1400 BCE to final centuries BCE by various scholars according to astronomical and linguistic evidences. Chinese astrology was elaborated in the Zhou dynasty (1046–256 BCE). Hellenistic astrology after 332 BCE mixed Babylonian astrology with Egyptian Decanic astrology in Alexandria, creating horoscopic astrology. Alexander the Great's conquest of Asia allowed astrology to spread to Ancient Greece and Rome. In Rome, astrology was associated with "Chaldean wisdom". After the conquest of Alexandria in the 7th century, astrology was taken up by Islamic scholars, and Hellenistic texts were translated into Arabic and Persian. In the 12th century, Arabic texts were imported to Europe and translated into Latin. Major astronomers including Tycho Brahe, Johannes Kepler and Galileo practised as court astrologers. Astrological references appear in literature in the works of poets such as Dante Alighieri and Geoffrey Chaucer, and of playwrights such as Christopher Marlowe and William Shakespeare.
Throughout most of its history, astrology was considered a scholarly tradition. It was accepted in political and academic contexts, and was connected with other studies, such as astronomy, alchemy, meteorology, and medicine. At the end of the 17th century, new scientific concepts in astronomy and physics (such as heliocentrism and Newtonian mechanics) called astrology into question. Astrology thus lost its academic and theoretical standing, and common belief in astrology has largely declined.
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