General PC Terms

The list of terms contained on this site is not meant to be "all encompassing."  Instead, only common terms the average user might need can be found on this page.  All terms are listed alphabetically.  If you are looking for a definition you can't find, e-mail us and we will send you the definition and add it to our site.

AGP - Short for Accelerated Graphics Port, an interface specification developed by Intel Corporation.  AGP is based on PCI, but is designed especially for the throughput demands of 3-D graphics.  Rather than using the PCI bus for graphics data, AGP introduces a dedicated point-to-point channel so that the graphics controller can directly access main memory.  The AGP channel is 32 bits wide and runs at 66 MHz.  This translates into a total bandwidth of 266 MBps, as opposed to the PCI bandwidth of 133 MBps.  AGP also supports two optional faster modes, with throughputs of 533 MBps and 1.07 GBps.  In addition, AGP allows 3-D textures to be stored in main memory rather than video memory.

API - Abbreviation of Application Program Interface, a set of routines, protocols, and tools for building software applications.  A good API makes it easier to develop a program by providing all the building blocks.  A programmer puts the blocks together.  Most operating environments, such as MS-Windows, provide an API so that programmers can write applications consistent with the operating environment. Although APIs are designed for programmers, they are ultimately good for users because they guarantee that all programs using a common API will have similar interfaces.  This makes it easier for users to learn new programs.

BOOT - Short for Bootstrap.  To load the first piece of software that starts a computer.  Because the operating system is essential for running all other programs, it is usually the first piece of software loaded during the boot process.

BANDWIDTH - The amount of data that can be transmitted in a fixed amount of time.  For digital devices, the bandwidth is usually expressed in bits per second (bps) or bytes per second.  For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz).  The bandwidth is particularly important for I/O devices.  For example, a fast disk drive can be hampered by a bus with a low bandwidth.  This is the main reason that new buses, such as AGP, have been developed for the PC.

BIOS - An acronym for Basic Input/Output System.  The BIOS is built-in software that determines what a computer can do without accessing programs from a disk.  On PCs, the BIOS contains all the code required to control the keyboard, display screen, disk drives, serial communications, and a number of miscellaneous functions.  The BIOS is typically placed in a ROM chip that comes with the computer (it is often called a ROM BIOS).  This ensures that the BIOS will always be available and will not be damaged by disk failures.  It also makes it possible for a computer to boot itself.  Many modern PCs have a flash BIOS, which means that the BIOS has been recorded on a flash memory chip, which can be updated if necessary.  The PC BIOS is fairly standardized, so all PCs are similar at this level (although there are different BIOS versions). Additional DOS functions are usually added through software modules.  This means you can upgrade to a newer version of DOS without changing the BIOS.

BPS - Abbreviation of Bits Per Second, the standard measure of data transmission speeds.

BUS - A collection of wires through which data is transmitted from one part of a computer to another.  You can think of a bus as a highway on which data travels within a computer.  When used in reference to personal computers, the term bus usually refers to internal bus.  This is a bus that connects all the internal computer components to the CPU and main memory.  There's also an expansion bus that enables expansion boards to access the CPU and memory.  All buses consist of two parts -- an address bus and a data bus. The data bus transfers actual data whereas the address bus transfers information about where the data should go.  The size of a bus, known as its width, is important because it determines how much data can be transmitted at one time.  For example, a 16-bit bus can transmit 16 bits of data, whereas a 32-bit bus can transmit 32 bits of data.  Every bus has a clock speed measured in MHz.  A fast bus allows data to be transferred faster, which makes applications run faster.  On PCs, the old ISA bus is being replaced by faster buses such as PCI.  Nearly all PCs made today include a local bus for data that requires especially fast transfer speeds, such as video data. The local bus is a high-speed pathway that connects directly to the processor.  Several different types of buses are used on Apple Macintosh computers. Older Macs use a bus called NuBus, but newer ones use PCI.

BYTE - Abbreviation for binary term, a unit of storage capable of holding a single character.  On almost all modern computers, a byte is equal to 8 bits.  Large amounts of memory are indicated in terms of kilobytes (1,024 bytes), megabytes (1,048,576 bytes), and gigabytes (1,073,741,824 bytes).

CDR - Short for Compact Disk Recordable.  A compact disc is a polycarbonate with one or more metal layers capable of storing digital information.

CD-RW - Short for CD-ReWritable disk, a type of CD disk that enables you to write onto it in multiple sessions.  One of the problems with CD-R disks is that you can only write to them once.  With CD-RW drives and disks, you can treat the optical disk just like a floppy or hard disk, writing data onto it multiple times.  The first CD-RW drives became available in mid-1997.  They can read CD-ROMs and can write onto today's CD-R disks, but they cannot write on normal CD-ROMs.  This means that disks created with a CD-RW drive can only be read by a CD-RW drive.  However, a new standard called MultiRead, developed jointly by Philips Electronics and Hewlett-Packard, will enable CD-ROM players to read disks created by CD-RW drives

CPU - Abbreviation of Central Processing Unit, and pronounced as separate letters.  The CPU is the brains of the computer. Sometimes referred to simply as the processor or central processor, the CPU is where most calculations take place.  In terms of computing power, the CPU is the most important element of a computer system.   On large machines, CPUs require one or more printed circuit boards.  On personal computers and small workstations, the CPU is housed in a single chip called a microprocessor.   Two typical components of a CPU are:   The arithmetic logic unit (ALU), which performs arithmetic and logical operations.   The control unit, which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary.

DDR - Short for Double Data Rate synchronous DRAM, a type of SDRAM that supports data transfers on both edges of each clock cycle (the rising and falling edges), effectively doubling the memory chip's data throughput.  DDR-SDRAM also consumes less power, which makes it well-suited to notebook computers.  DDR-SDRAM is also called SDRAM II.

DIMM - Short for Dual In-line Memory Module, a small circuit board that holds memory chips. A single in-line memory module (SIMM) has a 32-bit path to the memory chips whereas a DIMM has 64-bit path.  Because the Pentium processor requires a 64-bit path to memory, you need to install SIMMs two at a time. With DIMMs, you can install memory one DIMM at a time.

DRAM - Short for Dynamic Random Access Memory, a type of memory used in most personal computers..

DVD+R - Short for DVD+Recordable, a recordable DVD format similar to CD-R.  A DVD+R can only record data once and then the data becomes permanent on the disc.  The disc can not be recorded onto a second time. DVD+R and DVD+RW formats are supported by Philips, Sony, Hewlett-Packard, Dell, Ricoh, Yamaha and others

DVD-R - Short for Short for DVD-Recordable, a recordable DVD format similar to CD-R.  A DVD-R can only record data once and then the data becomes permanent on the disc.  The disc can not be recorded onto a second time.  There also are two additional standards for DVD-R disks: DVD-RG for general use, and DVD-RA for authoring, which is used for mastering DVD video or data and is not typically available to the general public.  DVD-R, DVD-RW and DVD-RAM are supported by Panasonic, Toshiba, Apple Computer, Hitachi, NEC, Pioneer, Samsung and Sharp.  These formats are also supported by the DVD Forum.

DVD+RW - Short for DVD+ReWritable, a re-recordable DVD format similar to CD-RW.  The data on a DVD+RW disc can be erased and recorded over numerous times without damaging the medium.  DVD+RW and DVD+R formats are supported by Philips, Sony, Hewlett-Packard, Dell, Ricoh, Yamaha and others.

DVD-RW - Short for DVD-ReWritable, a re-recordable DVD format similar to DVD+RW.  The data on a DVD-RW disc can be erased and recorded over numerous times without damaging the medium.  DVD-R, DVD-RW and DVD-RAM are supported by Panasonic, Toshiba, Apple Computer, Hitachi, NEC, Pioneer, Samsung and Sharp.  These formats are also supported by the DVD Forum.

EDO - Short for Extended Data Out dynamic random access memory, a type of DRAM that is faster than conventional DRAM.  Unlike conventional DRAM which can only access one block of data at a time, EDO RAM can start fetching the next block of memory at the same time that it sends the previous block to the CPU.

EIDE - Short for Enhanced Intelligent Drive Electronics or Integrated Drive Electronics, depending on who you ask.  An IDE interface is an interface for mass storage devices, in which the controller is integrated into the disk or CD-ROM drive.  A newer version of the IDE mass storage device interface standard developed by Western Digital Corporation.  It supports data rates of between 4 and 16.6 MBps, about three to four times faster than the old IDE standard.  In addition, it can support mass storage devices of up to 8.4 gigabytes, whereas the old standard was limited to 528 MB.  Because of its lower cost, enhanced EIDE has replaced SCSI in many areas.  EIDE is sometimes referred to as Fast ATA or Fast IDE, which is essentially the same standard, developed and promoted by Seagate Technologies.  It is also sometimes called ATA-2.  There are four EIDE modes defined.  The most common is Mode 4, which supports transfer rates of 16.6 MBps.  There is also a new mode, called ATA-3 or Ultra ATA, that supports transfer rates of 33 MBps.

 FIREWIRE (1394) - A very fast external bus standard that supports data transfer rates of up to 400Mbps (in 1394a) and 800Mbps (in 1394b).  Products supporting the 1394 standard go under different names, depending on the company.  Apple, which originally developed the technology, uses the trademarked name FireWire.  Other companies use other names, such as i.link and Lynx, to describe their 1394 products.  A single 1394 port can be used to connect up 63 external devices.  In addition to its high speed, 1394 also supports isochronous data -- delivering data at a guaranteed rate.  This makes it ideal for devices that need to transfer high levels of data in real-time, such as video devices.  Although extremely fast and flexible, 1394 is also expensive.  Like USB, 1394 supports both Plug-and-Play and hot plugging, and also provides power to peripheral devices.

G - The symbol used for Giga or gigabyte.

GPU - Acronym for Graphic Display Unit.  Used primarily for 3-D applications, a graphics processing unit is a single-chip processor that creates lighting effects and transforms objects every time a 3D scene is redrawn.  These are mathematically-intensive tasks, which otherwise, would put quite a strain on the CPU.  Lifting this burden from the CPU frees up cycles that can be used for other jobs.  The first company to develop the GPU is NVIDIA Inc.  Its GeForce 256 GPU is capable of billions of calculations per second, can process a minimum of 10 million polygons per second, and has over 22 million transistors, compared to the 9 million found on the Pentium III.  Its workstation version called the Quadro, designed for CAD applications, can process over 200 billion operations a second and deliver up to 17 million triangles per second.  The GeForce NVIDIA GPU card is compatible with the following graphics APIs :  OpenGL and Microsoft's DirectX, Intel's Accelerated Graphics Port (AGP) technology and AMD 's 3DNow!  The Quadro is an OpenGL specific card with driver support for Pentium III Xeon and AMD Athlon CPUs.

HARD DRIVE - The mechanism that reads and writes data on a hard disk. Hard disk drives (HDDs) for PCs generally have seek times of about 12 milliseconds or less. Many disk drives improve their performance through a technique called caching.  There are several interface standards for passing data between a hard disk and a computer. The most common are IDE and SCSI.  Hard disk drives are sometimes called Winchester drives, Winchester being the name of one of the first popular hard disk drive technologies developed by IBM in 1973.

I / O - Short for Input/Output.  The term I/O is used to describe any program, operation or device that transfers data to or from a computer and to or from a peripheral device.  Every transfer is an output from one device and an input into another.  Devices such as keyboards and mice are input-only devices while devices such as printers are output-only.  A writable CD-ROM is both an input and an output device.

ISA - Sort for Industry Standard Architecture.  The bus architecture used in the IBM PC/XT and PC/AT.  The AT version of the bus is called the AT bus and became a de facto industry standard.  Starting in the early 90s, ISA began to be replaced by the PCI local bus architecture.  Most computers made today include both an AT bus for slower devices and a PCI bus for devices that need better bus performance.  In 1993, Intel and Microsoft introduced a new version of the ISA specification called Plug and Play ISA.  Plug and Play ISA enables the operating system to configure expansion boards automatically so that users do not need to fiddle with DIP switches and jumpers.

K- Short for Kilo or kilobyte.

LAN - Short for Local Area Network.  A computer network that spans a relatively small area.  Most LANs are confined to a single building or group of buildings.  However, one LAN can be connected to other LANs over any distance via telephone lines and radio waves.  A system of LANs connected in this way is called a wide-area network (WAN).  Most LANs connect workstations and personal computers.  Each node (individual computer ) in a LAN has its own CPU with which it executes programs, but it also is able to access data and devices anywhere on the LAN.  This means that many users can share expensive devices, such as laser printers, as well as data.  Users can also use the LAN to communicate with each other, by sending e-mail or engaging in chat sessions.  There are many different types of LANs Ethernets being the most common for PCs.  Most Apple Macintosh networks are based on Apple's AppleTalk network system, which is built into Macintosh computers.  LANs are capable of transmitting data at very fast rates, much faster than data can be transmitted over a telephone line; but the distances are limited, and there is also a limit on the number of computers that can be attached to a single LAN.

LOCAL BUS -  A data bus that connects directly, or almost directly, to the microprocessor. Although local buses can support only a few devices, they provide very fast throughput. Modern PCs include both a PCI local bus and a more general ISA expansion bus for devices that do not require such fast data throughput.

M - Abbreviation for Mega or megabyte.

MEMORY  (RAM) - Internal storage areas in the computer. The term memory identifies data storage that comes in the form of chips, and the word storage is used for memory that exists on tapes or disks. Moreover, the term memory is usually used as a shorthand for physical memory, which refers to the actual chips capable of holding data. Some computers also use virtual memory, which expands physical memory onto a hard disk.  Every computer comes with a certain amount of physical memory, usually referred to as main memory or RAM. You can think of main memory as an array of boxes, each of which can hold a single byte of information. A computer that has 1 megabyte of memory, therefore, can hold about 1 million bytes (or characters) of information.  There are several different types of memory:  RAM (random-access memory):  This is the same as main memory.  When used by itself, the term RAM refers to read and write memory; that is, you can both write data into RAM and read data from RAM.  This is in contrast to ROM, which permits you only to read data.  Most RAM is volatile, which means that it requires a steady flow of electricity to maintain its contents.  As soon as the power is turned off, whatever data was in RAM is lost.    ROM (read-only memory):  Computers almost always contain a small amount of read-only memory that holds instructions for starting up the computer.  Unlike RAM, ROM cannot be written to.  PROM (programmable read-only memory):  A PROM is a memory chip on which you can store a program.  But once the PROM has been used, you cannot wipe it clean and use it to store something else.  Like ROMs, PROMs are non-volatile.  EPROM (erasable programmable read-only memory):  An EPROM is a special type of PROM that can be erased by exposing it to ultraviolet light.  EEPROM (electrically erasable programmable read-only memory):  An EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge.

MOTHERBOARD - The main circuit board of a microcomputer.  The motherboard contains the connectors for attaching additional boards.  Typically, the motherboard contains the CPU, BIOS, memory, mass storage interfaces, serial and parallel ports, expansion slots, and all the controllers required to control standard peripheral devices, such as the display screen, keyboard, and disk drive.  Collectively, all these chips that reside on the motherboard are known as the motherboard's chipset.  On most PCs, it is possible to add memory chips directly to the motherboard.  You may also be able to upgrade to a faster PC by replacing the CPU chip. To add additional core features, you may need to replace the motherboard entirely.   Motherboard is sometimes abbreviated as mobo.

OPERATING SYSTEM (O / S) -  The most important program that runs on a computer.  Every general-purpose computer must have an operating system to run other programs.  Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.  For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop -- it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system.  Operating systems can be classified as follows:  Multi-user : Allows two or more users to run programs at the same time.  Some operating systems permit hundreds or even thousands of concurrent users.  Multiprocessing :  Supports running a program on more than one CPU.  Multitasking :  Allows more than one program to run concurrently.   Multithreading :  Allows different parts of a single program to run concurrently.   Real time :  Responds to input instantly. General-purpose operating systems, such as DOS and UNIX, are not real-time.  Operating systems provide a software platform on top of which other programs, called application programs, can run.  The application programs must be written to run on top of a particular operating system.  Your choice of operating system, therefore, determines to a great extent the applications you can run.  For PCs, the most popular operating systems are DOS, OS/2, and Windows, but others are available, such as Linux.  As a user, you normally interact with the operating system through a set of commands.  For example, the DOS operating system contains commands such as COPY and RENAME for copying files and changing the names of files, respectively.  The commands are accepted and executed by a part of the operating system called the command processor or command line interpreter.  Graphical user interfaces, such as Windows, allow you to enter commands by pointing and clicking at objects that appear on the screen.

PC - Short for Personal Computer or IBM PC.  The first personal computer produced by IBM was called the PC, and increasingly the term PC came to mean IBM or IBM-compatible personal computers, to the exclusion of other types of personal computers, such as Macintoshes.  In recent years, the term PC has become more and more difficult to pin down.  In general, though, it applies to any personal computer based on an Intel microprocessor, or on an Intel-compatible microprocessor.  For nearly every other component, including the operating system, there are several options, all of which fall under the rubric of PC

PCI - Acronym for Peripheral Component Interconnect, a local bus standard developed by Intel Corporation.  Most modern PCs include a PCI bus in addition to a more general ISA expansion bus.  PCI is also used on newer versions of the Macintosh computer.  PCI is a 64-bit bus, though it is usually implemented as a 32-bit bus.  It can run at clock speeds of 33 or 66 MHz. At 32 bits and 33 MHz, it yields a throughput rate of 133 MBps.   Although it was developed by Intel, PCI is not tied to any particular family of microprocessors.

RAM - Acronym for Random Access Memory, a type of computer memory that can be accessed randomly; that is, any byte of memory can be accessed without touching the preceding bytes.  RAM is the most common type of memory found in computers and other devices, such as printers.  There are two basic types of RAM:  dynamic RAM (DRAM)  and static RAM (SRAM)   The two types differ in the technology they use to hold data, dynamic RAM being the more common type.  Dynamic RAM needs to be refreshed thousands of times per second.  Static RAM does not need to be refreshed, which makes it faster; but it is also more expensive than dynamic RAM.  Both types of RAM are volatile, meaning that they lose their contents when the power is turned off.   In common usage, the term RAM is synonymous with main memory, the memory available to programs.  For example, a computer with 8MB RAM has approximately 8 million bytes of memory that programs can use.  In contrast, ROM (read-only memory) refers to special memory used to store programs that boot the computer and perform diagnostics.  Most personal computers have a small amount of ROM (a few thousand bytes).  In fact, both types of memory (ROM and RAM) allow random access.  To be precise, therefore, RAM should be referred to as read/write RAM and ROM as read-only RAM.

RAMBUS (RDRAM) - Short for Rambus DRAM, a type of memory (DRAM) developed by Rambus, Inc.  Whereas the fastest current memory technologies used by PCs (SDRAM) can deliver data at a maximum speed of about 100 MHz, RDRAM transfers data at up to 800 MHz.  In 1997, Intel announced that it would license the Rambus technology for use on its future motherboards, thus making it the likely de facto standard for memory architectures.  However, a consortium of computer vendors is working on an alternative memory architecture called SyncLink DRAM (SLDRAM).  RDRAM is already being used in place of VRAM in some graphics accelerator boards.  As of late 1999, Intel has been using RDRAM in its Pentium III Xeon processors and more recently in its Pentium 4 processors.  Intel and Rambus are also working a new version of RDRAM, called nDRAM, that will support data transfer speeds at up to 1,600 MHz.

ROM - Acronym for Read Only Memory, computer memory on which data has been prerecorded. Once data has been written onto a ROM chip, it cannot be removed and can only be read.   Unlike main memory (RAM), ROM retains its contents even when the computer is turned off. ROM is referred to as being nonvolatile, whereas RAM is volatile.  Most personal computers contain a small amount of ROM that stores critical programs such as the program that boots the computer.  In addition, ROMs are used extensively in calculators and peripheral devices such as laser printers, whose fonts are often stored in ROMs.  A variation of a ROM is a PROM (programmable read-only memory).

SCSI - Acronym for Small Computer System Interface.  SCSI is a parallel interface standard used by Apple Macintosh computers, PCs, and many UNIX systems for attaching peripheral devices to computers.  Nearly all Apple Macintosh computers, excluding only the earliest Macs and the recent iMac, come with a SCSI port for attaching devices such as disk drives and printers.  SCSI interfaces provide for faster data transmission rates (up to 80 megabytes per second) than standard serial and parallel ports.  In addition, you can attach many devices to a single SCSI port, so that SCSI is really an I/O bus rather than simply an interface.  Although SCSI is an ANSI standard, there are many variations of it, so two SCSI interfaces may be incompatible.  For example, SCSI supports several types of connectors.   While SCSI has been the standard interface for Macintoshes, the iMac comes with IDE, a less expensive interface, in which the controller is integrated into the disk or CD-ROM drive.  Other interfaces supported by PCs include enhanced IDE and ESDI for mass storage devices, and Centronics for printers.  You can, however, attach SCSI devices to a PC by inserting a SCSI board in one of the expansion slots.  Many high-end new PCs come with SCSI built in.  Note, however, that the lack of a single SCSI standard means that some devices may not work with some SCSI boards.  The following varieties of SCSI are currently implemented:   SCSI-1: Uses an 8-bit bus, and supports data rates of 4 MBps.  SCSI-2: Same as SCSI-1, but uses a 50-pin connector instead of a 25-pin connector, and supports multiple devices.  This is what most people mean when they refer to plain SCSI.   Wide SCSI: Uses a wider cable (168 cable lines to 68 pins) to support 16-bit transfers.  Fast SCSI: Uses an 8-bit bus, but doubles the clock rate to support data rates of 10 MBps.  Fast Wide SCSI: Uses a 16-bit bus and supports data rates of 20 MBps.  Ultra SCSI: Uses an 8-bit bus, and supports data rates of 20 MBps.  SCSI-3: Uses a 16-bit bus and supports data rates of 40 MBps.  Also called Ultra Wide SCSI.  Ultra2 SCSI: Uses an 8-bit bus and supports data rates of 40 MBps.  Wide Ultra2 SCSI: Uses a 16-bit bus and supports data rates of 80 MBps.

SDRAM - Short for Synchronous Dynamic Random Access Memory, a type of DRAM that can run at much higher clock speeds than conventional memory.  SDRAM actually synchronizes itself with the CPU's bus and is capable of running at 133 MHz, about three times faster than conventional FPM RAM, and about twice as fast EDO DRAM.  SDRAM is replacing EDO DRAM in many newer computers.

SIMM - Acronym for Single In-line Memory Module, a small circuit board that can hold a group of memory chips.  Typically, SIMMs hold up 8 (on Macintoshes) or 9 (on PCs) RAM chips. On PCs, the ninth chip is often used for parity error checking.  Unlike memory chips, SIMMs are measured in bytes rather than bits. SIMMs are easier to install than individual memory chips.  The bus from a SIMM to the actual memory chips is 32 bits wide.  A newer technology, called dual in-line memory module (DIMM), provides a 64-bit bus.  For modern Pentium microprocessors that have a 64-bit bus, you must use either DIMMs or pairs of SIMMs. 

ULTRA / ATA - Short for Ultra Advanced Technology Attachment, a disk drive implementation that integrates the controller on the disk drive itself.  There are several versions of ATA, all developed by the Small Form Factor (SFF) Committee:  ATA: Known also as IDE, supports one or two hard drives, a 16-bit interface and PIO modes 0, 1 and 2.  ATA-2: Supports faster PIO modes (3 and 4) and multiword DMA modes (1 and 2).  Also supports logical block addressing (LBA) and block transfers. ATA-2 is marketed as Fast ATA and Enhanced IDE (EIDE).   ATA-3: Minor revision to ATA-2.  Ultra-ATA: Also called Ultra-DMA, ATA-33, and DMA-33, supports multiword DMA mode 3 running at 33 MBps.   ATA/66: A version of ATA proposed by Quantum Corporation, and supported by Intel, that doubles ATA's throughput to 66 MBps.  ATA/100: An updated version of ATA/66 that increases data transfer rates to 100 MBps.  ATA/133: An updated version of ATA/100 that increases data transfer rates to 133MBps.  ATA is also is called Parallel ATA.

USB - Short for Universal Serial Bus, an external bus standard that supports data transfer rates of 12 Mbps.  A single USB port can be used to connect up to 127 peripheral devices, such as mice, modems, and keyboards.  USB also supports Plug-and-Play installation and hot plugging.  Starting in 1996, a few computer manufacturers started including USB support in their new machines.  It wasn't until the release of the best-selling iMac in 1998 that USB became widespread.  It is expected to completely replace serial and parallel ports.  USB 2.0 is an updated version of USB and is also referred to as Hi-Speed USB.   USB 2.0 is an external bus that supports data rates up to 480Mbps.  USB 2.0 is an extension of USB 1.1.  USB 2.0 is fully compatible with USB 1.1 and uses the same cables and connectors.  Hewlett-Packard, Intel, Lucent, Microsoft, NEC and Philips jointly led the initiative to develop a higher data transfer rate than the 1.1 specification to meet the bandwidth demands of developing technologies.  The USB 2.0 specification was released in April 2000.

VGA - Abbreviation of Video Graphics Array, a graphics display system for PCs developed by IBM.  VGA has become one of the de facto standards for PCs.  In text mode, VGA systems provide a resolution of 720 by 400 pixels. In graphics mode, the resolution is either 640 by 480 (with 16 colors) or 320 by 200 (with 256 colors).  The total palette of colors is 262,144.   Unlike earlier graphics standards for PCs -- MDA, CGA, and EGA -- VGA uses analog signals rather than digital signals.  Consequently, a monitor designed for one of the older standards will not be able to use VGA.  Since its introduction in 1987, several other standards have been developed that offer greater resolution and more colors ( SVGA, 8514/A graphics standard, and XGA), but VGA remains the lowest common denominator. All PCs made today support VGA, and possibly some other more advanced standard.

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