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AGP Accelerated Graphics Port: an Intel-designed 32-bit PC bus architecture introduced in 1997 allowing graphics cards direct access to the system bus (currently up to 100MHz), rather than going through the slower 33MHz PCI bus. AGP uses a combination of frame buffer memory local to the graphics controller, as well as system memory, for graphics data storage, vastly increasing the amount of memory available for 3D textures.
ATA AT Attachment: the specification, formulated in the 1980s by a consortium of hardware and software manufacturers, that defines the IDE drive interface. AT refers to the IBM PC/AT personal computer and its bus architecture. IDE drives are sometimes referred to as ATA drives or AT bus drives. The newer ATA-2 specification defines the EIDE interface, which improves upon the IDE standard. See also IDE and EIDE.
ATAPI Advanced Technology Packet Interface: a specification that defines device side characteristics for an IDE connected peripheral, such as CD-ROM or tape drives. ATAPI is essentially an adaptation of the SCSI command set to the IDE interface.
ATX Today’s predominant motherboard form factor. It improves on the previous standard, the Baby AT form factor, by rotating the orientation of the board 90 degrees. This allows for a more efficient design, with disk drive cable connectors nearer to the drive bays and the CPU closer to the power supply and cooling fan.
BIOS Basic Input Output System: a set of low-level routines in a computer's ROM that application programs (and operating systems) can use to read characters from the keyboard, output characters to printers, and interact with the hardware in other ways. It also provides the initial instructions for POST (Power On Self-Test) and booting the system files.
DMA Direct Memory Access: a process by which data moves directly between a disk drive (or other device) and system memory without requiring the involvement of the CPU, thus allowing the system to continue processing other tasks while the new data is being retrieved.
IRQ An Interrupt ReQuest signal is generated by a device to request processing time from the CPU. Each time a keyboard button is pressed or a character is printed to a screen, an IRQ is generated by the requesting device. No two devices can share the same IRQ. A PC has 16 IRQs.
PCI Peripheral Component Interface: the 32-bit bus architecture (64-bit with multiplexing), developed by DEC, IBM, Intel, and others, that is widely used in Pentium-based PCs. A PCI bus provides a high-bandwidth data channel between system board components such as the CPU and devices such as hard disks and video adapters. Superseded the VL-Bus, which was widely used in 486 PCs in the early 1990s.
PS/2 An IBM personal computer series introduced in 1987, superseding the original PC line. It introduced the 3.5in floppy disk, VGA graphics and Micro Channel bus. The latter has since given way to the PCI bus.
SCSI Small Computer System Interface: an American National Standards Institute (ANSI) interface between the computer and peripheral controllers. SCSI excels at handling large hard disks and permits up to eight devices to be connected along a single bus provided by a SCSI connection. The original 1986 SCSI-1 standard is now obsolete and references to 'SCSI' generally refer to the 'SCSI-2' variant. Also features in Narrow, Wide and UltraWide flavours. See also IDE.
ALU Arithmetic and Logic Unit: the smart part of a processor chip that performs commands like adding, subtracting, multiplying and dividing. It also knows how to read logic commands like OR, AND, or NOT. Messages from the Control Unit instruct the ALU what to do and then it takes data from its close companion, the Registers, to perform the task.
CISC Pronounced 'sisk' and standing for Complex Instruction Set Computer, this relates to a microprocessor architecture that favours the richness of the instruction set (typically as many as 200 unique instructions) over the speed with which individual instructions are executed.
RISC Reduced Instruction Set Computer: a microprocessor architecture that recognises a relatively limited number of instructions, favouring the speed at which individual instructions execute over the richness of the instruction set.
CONTROL UNIT The Control Unit is one of the most important parts of the microprocessor because it is in charge of the entire process. Based on instructions from the Decode Unit, it creates control signals that tell the Arithmetic Logic Unit (ALU) and the Registers how to operate, what to operate on, and what to do with the result. The Control Unit makes sure everything happens in the right place at the right time.
MMX MultiMedia eXtensions: Intel's upgraded Pentium processor which incorporates additional instructions designed specifically for processing multimedia data more efficiently and a larger 32Mb on-board cache. Codenamed P55C.
REGISTERS The Registers are a mini-storage area for data used by the Arithmetic Logic Unit (ALU) to complete the tasks the Control Unit has requested. The data can come from the data cache, main memory or the control unit and are all stored at special locations within the Registers. This makes retrieval for the ALU quick and efficient.
SEMICONDUCTOR A solid-state substance with conductive properties that can be altered with electricity. Silicon performs as a semiconductor when chemically combined with other elements. A semiconductor is also halfway between a conductor and an insulator. When charged with electricity or light, semiconductors change their state from non-conductive to conductive or vice versa. The most significant product built from a semiconductor is the transistor.
SUPERSCALAR A CPU architecture that allows more than one instruction to be executed in one clock cycle. Processors can do this by fetching multiple instructions in one cycle, deciding which instructions are independent of other instructions, and executing them.
TRANSISTOR A device used to amplify a signal or open and close a circuit. In a computer, it functions as an electronic switch, or bridge. The transistor contains a semiconductor material that can change its electrical state when pulsed. Invented in 1947 at Bell Labs, transistors have become the key ingredient of all digital circuits, including computers.
ACTIVE MOVIE Microsoft software component for handling and displaying digital video, including AVI, MPEG, and QuickTime. Incorporated into Windows 98 it is intended to replace Video for Windows. Renamed DirectShow in 1997.
ActiveX Microsoft’s object technology for the Web, will allow smooth animations and interactivity over the Internet.
AVI Audio Video Interleaved: Microsoft's file format for digital video and audio under Windows. Blocks of video and audio data are interspersed together in this format. It is cross-platform compatible, allowing *.AVI video files to be played under other operating systems.
CGI Common Gateway Interface: a standard method of extending Web server functionality by executing programs or scripts on a Web server in response to Web browser requests. A common use of CGI is in form processing, where the browser sends the form data to a CGI script on the server, and the script integrates the data with a database and sends back a results page as HTML.
DirectX This Microsoft Windows API was designed to provide software developers with direct access to low-level functions on PC peripherals. Before DirectX, programmers usually opted for the DOS environment, which was free of the limited multimedia feature set that characterised Windows for many years.
Java Script Netscape’s simple scripting language for Web pages which allows simple interactivity to be built into a page.
MPEG Moving Picture Experts Group: a standards committee, supported by the ISO, formed to establish uniform methodologies and algorithms for digital audio and video compression.
PDF Portable Document Format: Acrobat file format containing embedded fonts and graphics.
URL Uniform Resource Locator: a logical address that identifies a resource on the Internet.
VHS A VCR format introduced by JVC in 1976 to compete with Sony's Beta format. VHS subsequently become the standard for home and industry, and Beta became obsolete. S-VHS (Super VHS) is a subsequent format that improves resolution.
WWW World Wide Web: a collection of richly formatted graphic/hypermedia documents located on computers around the world and logically linked together by the Internet. With a graphical Web browser users can 'surf' the Web by clicking highlighted words on the screen. Each click activates a hypertext link, connecting the user to another Web location identified by a URL.
16-BIT AUDIO A unit of measure that indicates the resolution of a digitised sound sample. The higher the resolution, the better the audio fidelity. 16-bit audio is the standard used for standard audio Compact Discs (CD-DA).
3D SOUND A blanket term for technologies that alter the way sound is distributed in real-world space. Spatialisation broadens the soundstage (the area in space where the sound seems to be coming from), making it more dramatic and spacious, and gives the illusion of pushing it beyond the physical location of the speakers. Positional audio uses encoded audio streams to position sounds realistically in the space around the listener when the sounds are played back on compatible equipment.
DOLBY DIGITAL A digital audio encoding system from Dolby used in movie and home theaters. First used in 1995, Dolby Digital employs Dolby's AC-3 (Audio Coding-3) coding and compression technology and provides six channels of audio, known as 5.1 for front left, front right, front center, rear left, rear right and subwoofer.
MIDI Musical Instrument Digital Interface: a specification that standardises the interface between computers and digital devices that simulate musical instruments. Rather than transmit bulky digitised sound samples, a computer generates music on a MIDI synthesiser by sending it commands just a few bytes in length. These contain all the information a sound board needs to reproduce the desired sound - the type of instrument, the pitch, duration, volume, attack, decay, etc. are all specified by the protocol. Each channel of a MIDI synthesiser corresponds to a different instrument, or 'voice'. Programming several channels simultaneously produces symphonic sound.
MP3 Standardised as ISO-MPEG Audio Layer-3 (IS 11172-3 and IS 138-3), MP3 employs a lossy compression technique, with bits of information being discarded to allow data to be compressed into files which are relatively small in comparison with WAV files but which retain subjective CD quality.
TAPI Telephony Application Programming Interface: permits Windows applications to program telephone-line-based devices such as modems and fax machines in a device-independent manner.
WAV Waveform Audio: the native digital audio format used in Windows. WAV files use the .wav file extension and allow different sound qualities to be recorded. Either 8-bit or 16-bit samples can be taken at rates of 11025Hz, 22050Hz and 44100Hz. The highest quality (16-bit samples at 44100Hz) uses 88KB of storage per second.