The computer's power supply unit (PSU) turns the mains voltage (110 V or 240 V alternating current) into the different direct current voltages required by the computer's components. For personal computers, there are three types of PSU still in use: AT, ATX and ATX-2. ATX-2 is the most recent standard. AT is only in use in the oldest personal computers. A bay is a shelf or an opening used for the installation of drives into the computer(Ex. Hard drive or DVD drive). A computer may come equipped with 4 to 8 bays, empty bays are covered by a panel.When the bay is accessible its open to the outside of the PC, and if its hidden its closed inside the PC case. CD-ROM (an abbreviation of "Compact Disc Read-Only Memory") is a compact disc that contains data accessible by a computer. While the compact disc format was originally designed for music storage and playback, the format was later adapted to hold any form of binary data. CD-ROMs are popularly used to distribute computer software, including games and multimedia applications, though any data can be stored . Some CDs hold both computer data and audio with the latter capable of being played on a CD player, whilst data is only usable on a computer. These are called Enhanced CDs. There are several formats used for data stored on compact discs, known collectively as the Rainbow Books. These include the original Red Book standards for CD audio, White Book and Yellow Book CD-ROM[1]. ISO 9660 defines the standard file system of a CD-ROM, although it is due to be replaced by ISO 13490. UDF format is used on user-writeable CD-R and CD-RW discs that are intended to be extended or overwritten. The bootable CD specification, to make a CD emulate a hard disk or floppy, is called El Torito The Motherboard is a flat circuit board housed in the computer's case. Several indispensable computer components such as microprocessors chips, RAM chips,ROM chips, expansion slots, and co-processor slots operate from the motherboard, which according to the Using Information Technology text is akin to the central nervous system. It contains a number of components that are critical to the function of the computer. Let's explore some of these components in more detail starting with the microprocessors or Central Processing Unit. CPU is the computer's brain. It converts data into information which tells the computer what to do. For example, when you left click on the Windows Explorer Icon on your desk top. This command is first sent to the CPU which relays a message telling the Windows Explorer Icon to open. Even simple actions like typing "A" on the key pad must be processed by the CPU before it can appear on your screen. Some of the leading microprocessor or microchip makers are, Intel,IBM, and Apple. Random Access Memory or RAM is the main primary storage facility on you computer. It keeps information more readily accessible but stores it only temporarily.If your computer freezes or the power goes off, while you are working on a Word document for example, all your work will be lost. Thus, it is important to frequently save your work which will store your document in a secondary storage facility (hard drive) where it is retrievable even if your computer malfunctions. ROM or Read Only Memory is a nonvolatile storage facility where information cannot be readily added or removed by the user with out special knowledge. Instructions like how to start the computer or where to put icons on the desktop are stored here. The manufacturer puts these instructions in the ROM when the computer is being assembled. Flash Memory is nonvolatile memory that can be used by the computer or user. It can be erased electronically and rewritten. Most computers use flash memory for start-up instructions because it is easy to update. Flash memory is used in different portable devices such as mobile phones, digital cameras, portable digital media players and portable computers. Flash memory is also used in storage media such as flash memory cards and USB flash drives. The motherboard also houses expansion slots which allow the user to expand the computers capabilities. If you want to add a video card, sound card, fax machine or printer, the connectivity for these devices is found on the motherboard. All things considered, clearly the motherboard is an indispensable component of the computer.
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