V

V

V.120 n. The ITU-T (formerly CCITT) standard that governs serial communications over ISDN lines. Data is encapsulated using a protocol similar to the Lightweight Directory Access Protocol (LDAP), and more than one connection may be multiplexed on a communications channel. See also communications channel, communications protocol, International Telecommunications Union, ISDN, Lightweight Directory Access Protocol, multiplexing, standard (definition 1), V series.

V20, V30 n. NEC microprocessors that were slight improvements on Intel s 8088 and 8086, using the same command sets but different microcode.

V.2x, V.3x, V.4x, V.5x series n. See V series.

V.32terbo n. A modem protocol developed by AT&T for 19,200-bps modems, with fallback to the speeds supported by the ITU-T (formerly CCITT) V.32 standard. This protocol is proprietary to AT&T and was not adopted by CCITT or ITU-T. In the V series, V.34 takes the place of V.32terbo. See also International Telecommunications Union, V series.

V.34 n. Data transmission standard that provides for up to 28,800 bits per second (bps) communications over telephone lines. It defines a full-duplex (two-way) modulation technique and includes error-correcting and negotiation. See also bits per second, full-duplex, modulation standards, V.90.

V.42 n. The ITU-T (formerly CCITT) recommendation specifying procedures for error correction in data communications equipment (DCEs) designed for asynchronous-to-synchronous conversion. See also V series.

V.42bis n. The ITU-T (formerly CCITT) recommendation specifying procedures for data compression in data-circuit terminating equipment utilizing error-correction operations. See also V series.

V86 mode n. See virtual real mode.

V.90 n. Data transmission standard that provides for up to 56,000 bits per second (bps) communications over telephone lines. The transmission speed from the client-side modem for uploads is 33,600 bps. The transmission speed for downloads from the host-side modem such as an Internet service provider (ISP) or a corporate network is up to 56,000 bps, with an average speed of 40,000 to 50,000 bps. When the host-side modem does not support this standard, the alternative is V.34. See also bits per second, client, host, ISP, modem, modulation standards, V.34.

VAB n. See voice answer back.

VAC n. See volts alternating current.

vacuum tube n. A set of metal electrodes and intervening metal grids, contained in a glass or metal tube from which all gas has been removed. Voltages on the grids control electrical currents between the electrodes. Formerly used for amplification and switching in electronic circuits, vacuum tubes are now used in applications such as cathode-ray tubes and those requiring very high power levels. A vacuum tube is known as a valve in Great Britain.

validation server controls n. A set of server controls, included with ASP.NET, that verify user input. The input is checked as it comes from HTML server controls and Web server controls (for example, a Web page form) against programmer-defined requirements. Validation controls perform input checking in server code. If the user is working with a browser that supports DHTML, the validation controls can also perform validation using client script. See also ASP.NET server control, HTML server control, Web server control.

validation suite n. A set of tests that measures compliance with a standard, especially a standard definition of a programming language. See also standard (definition 1).

valid date interval n. A span of time during which a computer will maintain the correct date. For many PCs, the valid date interval is 1980 forward.

validity check n. The process of analyzing data to determine whether it conforms to predetermined completeness and consistency parameters.

value n. A quantity assigned to an element such as a variable, symbol, or label. See tone (definition 1).

value-added network n. A communications network that offers additional services, such as message routing, resource management, and conversion facilities, for computers communicating at different speeds or using different protocols. Acronym: VAN.

value-added reseller n. A company that buys hardware and software and resells it to the public with added services, such as user support. Acronym: VAR.

value list n. A list of values used by some application, such as a database, as a search string or as values for a filtered query. See also filter (definition 1), query (definition 1), search string.

value type n. A data type that is represented by the type s actual value. If a value type is assigned to a variable, that variable is given a fresh copy of the value. (This is in contrast to a reference type, where assignment does not create a copy.) Value types are usually created on a method s stack frame, rather than in the garbage-collected heap. A value type can be boxed, which is a process that creates a corresponding reference type. See also reference type.

valve n. See electron tube, vacuum tube.

vampire tap n. A type of transceiver used on Ethernet networks that is equipped with sharp metal prongs that pierce the insulation on thicknet cable to make contact with the copper core over which signals travel.

VAN n. See value-added network.

vanilla adj. See plain vanilla.

vaporware n. Software that has been announced but not released to customers. The term implies sarcastically that the product exists only in the minds of the marketing department. Compare freeware, shareware.

VAR n. See value-added reseller.

variable n. In programming, a named storage location capable of containing data that can be modified during program execution. See also data structure, data type, global variable, local variable. Compare constant.

variable expression n. An expression that depends on the value of at least one variable and, hence, must be evaluated during program execution. See also run time (definition 1), variable. Compare constant expression.

variable-length field n. In a record, a field that can vary in length according to how much data it contains. See also field (definition 1).

variable-length record n. A record that can vary in length because it contains variable-length fields, certain fields only under certain conditions, or both of these. See also variable-length field.

VAX n. Acronym for virtual address extension. A family of 32-bit minicomputers introduced by Digital Equipment Corporation in 1978. The VAX, like the later 68000 microprocessor, has a flat address space and a large instruction set. The VAX was highly favored within the hacker community but has been superseded by microprocessors and RISC workstations. See also flat address space, instruction set, microprocessor, minicomputer, RISC.

VBA n. See Visual Basic for Applications.

vBNS n. Short for very high-speed Backbone Network Service. A network connecting several supercomputer centers and reserved for high-performance, high-bandwidth scientific applications requiring massive computing power. The vBNS was developed by the National Science Foundation and MCI Telecommunications. It began operation in 1995, reaching speeds of 2.4 Gbps, using MCI s network of advanced switching and fiberoptic transmission technologies. Later, vBNS expanded to provide backbone services for Internet2.

VBScript n. See Visual Basic, Scripting Edition.

VBS/VBSWG virus n. Acronym for Visual Basic Script/Visual Basic Script Worm Generator virus. Any virus created using the VBSWG virus creation toolkit. The tools available in VBSWG worm kit allow individuals to write viruses without having significant computer knowledge. Homepage and the Anna Kournikova virus are examples of VBS/VBSWG viruses.

VBX n. Short for Visual Basic custom control. A software module that, when called by a Visual Basic application, produces a control that adds some desired feature to the application. A VBX is a separate executable file, usually written in C, that is dynamically linked to the application at run time and can be used by other applications, including some applications not developed in Visual Basic. Although VBX technology was developed by Microsoft, most VBXs have been written by third-party developers. VBXs are still in use, but the technology has been superseded by OCXs and ActiveX controls. See also control (definition 2), Visual Basic. Compare ActiveX controls, dynamic-link library, OCX.

VCACHE n. The disk caching software used with VFAT driver in Windows 9x. VCACHE uses 32-bit code, runs in protected mode, and automatically allocates space in RAM rather than requiring the user to reserve space for the cache. See also cache, driver, protected mode, RAM, VFAT.

vCalendar n. A specification defining the format for applications to exchange scheduling information. The vCalendar specification is based on existing industry standards, including international standards for representing dates and times, and permits the exchange of schedules and to-do lists of the sort users commonly enter into personal calendars. Like the companion vCard specification for electronic business cards, it was created by the versit consortium founded by Apple, AT&T, IBM, and Siemens. Handed off to the Internet Mail Consortium (IMC) in 1996, vCalendar is supported by numerous hardware and software vendors. See also vCard.

vCard n. A specification for creating an electronic business card (or personal-information card) and for the card itself. Designed to be exchanged through applications such as e-mail and teleconferencing, a vCard includes information such as name, address, telephone and fax number(s), and e-mail address. It can also include time-zone, geographic location, and multimedia data such as photographs, company logos, and sound clips. Based on the ITU s X.500 directory services specification, vCard was developed by versit, a consortium whose principal members include Apple, AT&T, IBM, and Siemens. The specification is under the guidance of the Internet Mail consortium Version 3.0 of the vCard specification has been approved as a proposed standard by the IETF. A companion specification known as vCalendar supports electronic exchange of scheduling information. See also vCalendar, X series.

V-chip n. Electronic chip for installation in a television, VCR, cable box, or stand-alone device to provide adults with the ability to block programming they deem inappropriate. Intended to provide parents with a means of controlling the programming viewed by children, the V-chip allows adults to screen programs based on a rating level transmitted in the portion of the TV signal known as the vertical blanking interval (the same portion that carries closed captioning information). When programs exceed the chosen level, the V-chip signals the television, which then displays an unauthorized to receive message on a blank screen.

VCOMM n. The communications device driver in Windows 9x that provides the interface between Windows-based applications and drivers on one side, and port drivers and modems on the other. See also driver.

VCPI n. See Virtual Control Program Interface.

VCR-style mechanism n. 1. A user interface for playing movie files that has controls similar to those on a videocassette recorder (VCR). 2. A type of motorized docking mechanism in which a laptop or notebook computer is physically locked into place by the docking station. The advantage to a VCR-style mechanism is that it provides an electrically consistent, secure bus connection. See also docking mechanism, docking station, laptop, portable computer.

VDD n. Acronym for virtual display device driver. See virtual device driver.

VDL n. Acronym for Vienna Definition Language. A meta language, containing both a syntactic and a semantic metalanguage, used to define other languages. See also metalanguage.

VDM n. See video display metafile.

VDSL n. Short for very-high-speed digital subscriber line. The high-speed version of the xDSL (digital subscriber line) communication technologies, all of which operate over existing phone lines. VDSL can deliver up to 52 Mbps downstream, but it is effective only within about 4500 to 5000 feet of the central exchange. The data delivery rate is, in fact, related to the distance the signal must travel. To attain a rate of 52 Mbps, for example, the subscriber must be within 1000 feet of the exchange office. At a distance of 3000 feet, the data rate drops to about 26 Mbps; and at 5000 feet, the data rate drops to about 13 Mbps. See also central office, xDSL.

VDT n. Acronym for video display terminal. A terminal that includes a CRT (cathode-ray tube) and keyboard. See also CRT.

VDU n. Acronym for video display unit. A computer monitor. See also monitor.

vector n. 1. In mathematics and physics, a variable that has both distance and direction. Compare scalar. 2. In computer graphics, a line drawn in a certain direction from a starting point to an endpoint, both of whose locations are identified by the computer using x-y-coordinates on a grid. Vectors are used in the output of some graphics programs instead of groups of dots (on paper) or pixels (on screen). See also vector graphics. 3. In data structures, a one-dimensional array a set of items arranged in a single column or row. See also array, matrix.

vector display n. A CRT (cathode-ray tube), commonly used in oscilloscopes and DVST (direct view storage tube) displays, that allows the electron beam to be arbitrarily deflected, based on x-y-coordinate signals. For example, to draw a line on a vector display, the video adapter sends signals to the X and Y yokes to move the electron beam over the path of the line; there is no background composed of scan lines, so the line drawn on the screen is not constructed of pixels. See also CRT, yoke. Compare raster display.

vector font n. A font in which the characters are drawn using arrangements of line segments rather than arrangements of bits. See also font. Compare bitmapped font.

vector graphics n. Images generated from mathematical descriptions that determine the position, length, and direction in which lines are drawn. Objects are created as collections of lines rather than as patterns of individual dots or pixels. Compare raster graphics.

Vector Markup Language n. See VML.

vector table n. See dispatch table.

Velocity Engine n. A component of Apple s Macintosh G4 processor that processes data in 128-bit chunks. The Velocity Engine is capable of over one gigaflop of floating-point operations per second.

Venn diagram n. A type of diagram, used to express the result of operations on sets, in which a rectangle represents the universe and circles inside the rectangle represent sets of objects. Relationships between sets are indicated by the positions of the circles in relation to one another. The Venn diagram is named after John Venn (1834 1923), an English logician at Cambridge University. See the illustration.

Venn diagram.

verbose adj. Displaying messages as English text rather than as concise (but cryptic) codes.

verify vb. To confirm either that a result is correct or that a procedure or sequence of operations has been performed.

Veronica n. Acronym for very easy rodent-oriented Netwide index to computerized archives. An Internet service developed at the University of Nevada that searches for Gopher archives by keywords. Users can enter Boolean operators, such as AND, OR, and XOR, to help narrow or expand their search. If any matching archives are found, they are listed on a new Gopher menu. See also Boolean operator, Gopher. Compare Archie, Jughead.

version n. A particular issue or release of a hardware product or software title.

version control n. The process of maintaining a database of all the source code and related files in a software development project to keep track of changes made during the project.

version number n. A number assigned by a software developer to identify a particular program at a particular stage, before and after public release. Successive public releases of a program are assigned increasingly higher numbers. Version numbers usually include decimal fractions. Major changes are generally marked by a change in the whole number, whereas for minor changes only the number after the decimal point increases.

verso adj. The publishing term for a left-hand page, which is always even-numbered. Compare recto.

vertex n. The highest point of a curve, the point where a curve ends, or the point where two line segments meet in a polygon or freeform.

vertical application n. A specialized application designed to meet the unique needs of a particular business or industry for example, an application to keep track of billing, tips, and inventory in a restaurant.

vertical bandwidth n. The rate at which a display screen is refreshed entirely, expressed in hertz (Hz). The vertical bandwidth of display systems ranges from 45 Hz to over 100 Hz. Also called: vertical scan rate, vertical sync, V-sync.

vertical blanking interval n. The time required for the electron beam in a raster-scan display to perform a vertical retrace. See also blanking, vertical retrace.

vertical recording n. See perpendicular recording.

vertical redundancy check n. See VRC.

vertical retrace n. On raster-scan displays, the movement of the electron beam from the lower right corner back to the upper left corner of the screen after the beam has completed a full sweep of the screen. See also blanking, vertical blanking interval. Compare horizontal retrace.

vertical scan rate n. See vertical bandwidth.

vertical scrolling n. Movement up or down in a displayed document. See also scroll bar.

vertical sync n. See vertical bandwidth.

vertical sync signal n. The part of a video signal to a raster display that denotes the end of the last scan line at the bottom of the display.

very-high-level language n. See 4GL.

very-high-rate digital subscriber line n. See VDSL.

very-high-speed integrated circuit n. An integrated circuit that performs operations, usually logic operations, at a very high speed. Acronym: VHSIC.

Very Large Database n. A database system containing volumes of data hundreds of gigabytes, or even terabytes, in size. A Very Large Database must often support thousands of users and tables with billions of rows of data, must often be able to operate across several different platforms and operating systems, and must often be able to work with many different software applications. Acronym: VLDB. See also data warehouse.

Very Large Memory n. A memory system designed to handle the huge data blocks associated with a Very Large Database. Very Large Memory uses 64-bit RISC technology to allow the use of addressable main memory and file sizes larger than 2 gigabytes (GB) and to cache as much as 14 GB of memory. Acronym: VLM. See also RISC, Very Large Database.

very-large-scale integration n. A reference to the density with which transistors and other elements are packed in an integrated circuit and to the thinness of the connections between them. Very-large-scale integration is generally considered to encompass the range from 5000 to 50,000 components. Acronym: VLSI. See also integrated circuit. Compare large-scale integration, medium-scale integration, small-scale integration, super-large-scale integration, ultra-large-scale integration.

Very Long Instruction Word n. See VLIW.

very-low-frequency electromagnetic radiation n. See VLF radiation.

VESA¹ adj. Having VL bus expansion slots. Also called: VLB. See also expansion slot, VL bus. Compare VESA/EISA, VESA/ISA.

VESA² n. Acronym for Video Electronics Standards Association. An organization of hardware manufacturers and vendors dedicated to drafting and improving standards for video and multimedia devices. Standards developed by VESA include the Display Data Channel (DDC), Display Power Management Signaling (DPMS), and VESA local bus (VL bus). See also DDC, DPMS, VL bus.

VESA DDC n. See DDC.

VESA Display Data Channel n. See DDC.

VESA Display Power Management Signaling n. See DPMS.

VESA/EISA adj. Having both EISA and VL bus expansion slots. See also EISA, expansion slot, VESA, VL bus. Compare VESA, VESA/ISA¹.

VESA/ISA adj. Having both ISA and VL bus expansion slots. See also expansion slot, ISA, VESA, VL bus. Compare VESA, VESA/EISA².

VESA local bus n. See VL bus.

vesicular film n. A coating for optical discs that facilitates erasing and rewriting. The surface is marked by small bumps, which can be flattened and thereby erased, rather than by the pits used in standard CD-ROM discs.

V.everything n. A marketing term used by some modem manufacturers to describe modems that comply with both the ITU-T (formerly CCITT) V.34 standard and the various proprietary protocols that were used before the standard was adopted, such as V.Fast Class. A V.everything modem should be compatible with any other modem that operates at the same speed. See also V.Fast Class, V series.

V.Fast Class n. A de facto modulation standard for modems implemented by Rockwell International prior to approval of the V.34 protocol, which is the standard. Although both V.Fast Class and V.34 are capable of 28.8-Kbps transmission, V.Fast Class modems cannot communicate with V.34 modems without an upgrade. Acronym: V.FC. See also V series.

VFAT n. Acronym for Virtual File Allocation Table. The file system driver software used under the Windows 9x Installable File System Manager (IFS) for accessing disks. VFAT is compatible with MS-DOS disks but runs more efficiently. VFAT uses 32-bit code, runs in protected mode, uses VCACHE for disk caching, and supports long filenames. See also Installable File System Manager, long filenames, protected mode, VCACHE, Windows. Compare file allocation table.

V.FC n. See V.Fast Class.

VGA n. Acronym for Video Graphics Adapter. A video adapter that duplicates all the video modes of the EGA (Enhanced Graphics Adapter) and adds several more. See also video adapter. Compare EGA.

VHLL n. Acronym for very-high-level language. See 4GL.

VHSIC n. See very-high-speed integrated circuit.

vi¹ n. Short for visual. The first full-screen text editor under UNIX. The vi editor offers many powerful but not very intuitive keyboard commands. It is still in use on UNIX systems, despite the existence of other editors such as Emacs. See also editor, UNIX.

vi² vb. To edit a file using the vi editor. See also vi¹.

VIA n. See Virtual Interface Architecture.

VI Architecture n. See Virtual Interface Architecture.

video adj. Of or pertaining to the visual component of a television signal. In relation to computers, video refers to the rendering of text and graphics images on displays. Compare audio.

video accelerator n. See graphics engine (definition 1).

video adapter n. The electronic components that generate the video signal sent through a cable to a video display. The video adapter is usually located on the computer s main system board or on an expansion board, but it is sometimes built into the terminal. Also called: video adapter board, video board, video card, video controller, video display adapter.

video adapter board n. See video adapter.

video board n. See video adapter.

video buffer n. The memory on a video adapter that is used to store data to be shown on the display. When the video adapter is in a character mode, this data is in the form of ASCII character and attribute codes; when it is in a graphics mode, the data defines each pixel. See also bit image, bit plane, color bits, pixel image.

video capture board n. See video capture device.

video capture card n. See video capture device.

video capture device n. An expansion board that converts analog video signals to digital form and stores them in a computer s hard disk or other mass storage device. Some video capture devices are also capable of converting digital video to analog video for use in a VCR. Also called: video capture board, video capture card. See also expansion board.

video card n. See video adapter.

video clip n. A file that contains a short video item, usually an excerpt from a longer recording.

video compression n. Reduction of the size of files containing video images stored in digital form. If no compression were done, 24-bit color video at 640 x 480 pixels would occupy almost one megabyte per frame, or over a gigabyte per minute. Video compression can, however, be lossy without affecting the perceived quality of the image. See also lossy compression, Motion JPEG, MPEG.

video conferencing n. Teleconferencing in which video images are transmitted among the various geographically separated participants in a meeting. Originally done using analog video and satellite links, today video conferencing uses compressed digital images transmitted over wide area networks or the Internet. A 56K communications channel supports freeze-frame video; with a 1.544-Mbps (T1) channel, full-motion video can be used. See also 56K, desktop conferencing, freeze-frame video, full-motion video, T1, teleconferencing. Compare data conferencing.

video controller n. See video adapter.

video digitizer n. A device used in computer graphics that uses a video camera, rather than a scan head, to capture a video image and then stores it in memory with the aid of a special-purpose circuit board. See also digitize. Compare digital camera.

videodisc n. An optical disc used to store video images and associated audio information. See also CD-ROM.

video display n. Any device capable of displaying, but not printing, text or graphics output from a computer.

video display adapter n. See video adapter.

video display board n. A video adapter implementation using an expansion board rather than the computer s main system board. See also video adapter.

video display card n. See video display board.

video display metafile n. A file containing video display information for the transport of images from one system to another. Acronym: VDM.

video display page n. A portion of a computer s video buffer that holds one complete screen image. If the buffer can hold more than one page, or frame, screen updates can be completed more rapidly because an unseen page can be filled while another is being displayed.

video display terminal n. See VDT.

video display tube n. See CRT.

video display unit n. See monitor.

video DRAM n. See video RAM.

video driver n. Software that provides the interface between the video adapter hardware and other programs, including the operating system. The user can access the video driver to specify the resolution and color-bit depth of images on the monitor during the setup process. See also driver, monitor, video adapter.

video editor n. A device or program used to modify the contents of a video file.

Video Electronics Standards Association n. See VESA².

video game n. See computer game.

Video Graphics Adapter or Video Graphics Array n. See VGA.

video graphics board n. A video adapter that generates video signals for displaying graphical images on a video screen.

video look-up table n. See color look-up table.

video memory n. Memory from which a display image is created, located in the video adapter or video subsystem. If both the video processor and the central processing unit (CPU) have access to video memory, images are produced by the CPU s modification of video memory. Video circuitry normally has priority over the processor when both attempt to read or write to a video memory location, so updating video memory is often slower than accessing main memory. See also video RAM.

video mode n. The manner in which a computer s video adapter and monitor display on-screen images. The most common modes are text (character) mode and graphics mode. In text mode, characters include letters, numbers, and some symbols, none of which are drawn on screen dot by dot. In contrast, graphics mode produces all screen images, whether text or art, as patterns of pixels (dots) that are drawn one pixel at a time.

videophone n. A device equipped with camera and screen, as well as a microphone and speaker, capable of transmitting and receiving video signals as well as voice over a telephone line. Using conventional telephone lines, a videophone can transmit only freeze-frame video. See also freeze-frame video.

video port n. A cable connector or port on a computer that outputs video signals to a monitor.

video RAM n. A special type of dynamic RAM (DRAM) used in high-speed video applications. Video RAM uses separate pins for the processor and the video circuitry, providing the video circuitry with a back door to the video RAM. The video circuitry can access the video RAM serially (bit by bit), which is more appropriate for transferring pixels to the screen than is the parallel access provided by conventional DRAM. Acronym: VRAM. See also dynamic RAM.

video server n. A server designed to deliver digital video-on-demand and other broadband interactive services to the public over a wide area network.

video signal n. The signal sent from a video adapter or other video source to a raster display. The signal can include horizontal and vertical synchronization signals, as well as image information. See also composite video display, RGB monitor.

video terminal n. See terminal (definition 1).

videotex n. An interactive information retrieval service designed to be accessed by subscribers over telephone lines. Information can be displayed on a home television screen or a videotex terminal. Subscribers use keypads to choose from menus and to request specific screens, or pages. Also called: videotext.

videotext n. See videotex.

Vienna Definition Language n. See VDL.

view¹ n. 1. The display of data or an image from a given perspective or location. 2. In relational database management systems, a logical table created through the specification of one or more relational operations on one or more tables. A view is equivalent to a divided relation in the relational model. See also relational database, relational model.

view² vb. To cause an application to display information on a computer screen.

viewer n. An application that displays or otherwise outputs a file in the same way as the application that created the file. An example of a viewer is a program to display the images stored in GIF or JPEG files. See also GIF, JPEG.

viewport n. In computer graphics, a view of a document or an image. A viewport is similar to the view in a window, but usually only part of the document or graphical image is visible. Compare window.

vine n. A means of distributing audiotape copies that is similar to a tape tree. Because vine tapes are digital in format, there is no degradation of sound quality as tapes are copied down the vine from one participant to the next. Compare tape tree.

Vines n. A UNIX-based networking operating system from Banyan Systems.

viral marketing n. A marketing concept that relies on computer users to distribute marketing materials, possibly without even being aware of their participation. Viral marketing is often tied in with free e-mail accounts or other free online services, from which users pass along advertisements with every message they send.

virgule n. The forward slash (/) character. Compare backslash.

virtual adj. Of or pertaining to a device, service, or sensory input that is perceived to be what it is not in actuality, usually as more real or concrete than it actually is.

virtual 8086 mode n. See virtual real mode.

virtual 86 mode n. See virtual real mode.

virtual address n. In a virtual memory system, the address that the application uses to reference memory. The memory management unit (MMU) translates this address into a physical address before the memory is actually read or written to. See also physical address, virtual memory. Compare real address.

virtual channel n. In Asynchronous Transfer Mode (ATM), the path taken by data sent from one sender to one receiver. See also ATM (definition 1), virtual path (definition 2).

virtual circuit n. A connection between communicating computers that provides the computers with what appears to be a direct link but can actually involve routing data over a defined but longer path.

virtual community n. See online community.

Virtual Control Program Interface n. A specification for MS-DOS programs to allow access to extended memory under a multitasking environment (for example, Windows) for 386 and higher-level processors. Acronym: VCPI. See also 80386DX, extended memory, multitasking. Compare protected mode.

virtual desktop n. A desktop enhancement tool that provides access to the desktop when it is covered by open windows or that expands the size of the working desktop. See also desktop.

virtual device n. A device that can be referenced but that does not physically exist. Virtual-memory addressing, for example, uses magnetic disk storage to simulate memory larger than that physically available.

virtual device driver n. Software in Windows 9x that manages a hardware or software system resource. If a resource retains information from one access to the next that affects the way it behaves when accessed (for example, a disk controller with its status information and buffers), a virtual device driver must exist for it. Virtual device drivers are described using three-letter abbreviations beginning with V and ending with D; the middle letter indicates the type of device, such as D for a display, P for a printer, T for a timer, and x when the type of device is not under discussion. Acronym: VD. See also device driver.

virtual disk n. See RAM disk.

virtual display device driver n. See virtual device driver.

Virtual File Allocation Table n. See VFAT.

virtual hosting n. A form of hosting that provides a Web server, communication, and other services to customers for their own Web sites. In addition to hardware, software, and communication, virtual hosting can include assistance with domain name registration, e-mail addresses, and other Web-related issues. See also host, hosting.

virtual image n. An image that is stored in computer memory but is too large to be shown in its entirety on the screen. Scrolling and panning are used to bring unseen portions of the image into view. See also virtual screen.

virtual-image file n. A file that specifies the material to be recorded onto a CD-ROM. A virtual-image file generally contains pointers to files that are distributed across a hard disk rather than gathered in one area. Since a complete copy of the material is not assembled, problems may occur in writing the CD-ROM due to delays in assembling the material from a scattered group of files. See also CD-ROM. Compare physical-image file.

Virtual Interface Architecture n. An interface specification that defines a standard low-latency, high-bandwidth means of communication between clusters of servers in a System Area Network (SAN). Developed by Compaq, Intel, Microsoft, and more than 100 industry groups, the Virtual Interface Architecture is processor and operating system independent. By reducing the time required for message-passing between applications and the network, it seeks to reduce overhead and thus deliver enterprise-level scalability for mission-critical applications. Acronym: VIA. Also called: VI Architecture. See also cluster, System Area Network.

virtual LAN n. Short for virtual local area network. A local area network consisting of groups of hosts that are on physically different segments but that communicate as though they were on the same wire. See also LAN.

virtual machine n. Software that mimics the performance of a hardware device, such as a program that allows applications written for an Intel processor to be run on a Motorola chip. Acronym: VM.

virtual memory n. Memory that appears to an application to be larger and more uniform than it is. Virtual memory may be partially simulated by secondary storage such as a hard disk. Applications access memory through virtual addresses, which are translated (mapped) by special hardware and software onto physical addresses. Acronym: VM. Also called: disk memory. See also paging, segmentation.

virtual monitor n. An enhanced monitor viewing system for visually impaired users that uses a virtual-reality headset to move enlarged text across the screen in a direction opposite to head motion. See also virtual reality.

virtual name space n. The set of all hierarchical sequences of names that can be used by an application to locate objects. One such sequence of names defines a path through the virtual name space, regardless of whether the hierarchy of names reflects the actual arrangement of objects around the system. For example, the virtual name space of a Web server consists of all possible URLs on the network on which it runs. See also URL.

virtual network n. A part of a network that appears to a user to be a network of its own. For example, an Internet service provider can set up multiple domains on a single HTTP server so that each one can be addressed with its company s registered domain name. See also domain name, HTTP server (definition 1), ISP.

virtual path n. 1. A sequence of names that is used to locate a file and that has the same form as a pathname in the file system but is not necessarily the actual sequence of directory names under which the file is located. The part of a URL that follows the server name is a virtual path. For example, if the directory c:\bar\sinister\forces\distance on the server miles is shared on the local area network at foo.com under the name \\miles\baz and contains the file elena.html, that file may be returned by a Web request for http://miles.foo.com/baz/elena.html. 2. In Asynchronous Transfer Mode (ATM), a set of virtual channels that are switched together as a unit through the network. See also ATM (definition 1), virtual channel.

virtual peripheral n. A peripheral that can be referenced but does not physically exist. For example, an application might treat a serial port through which data is being transmitted as a printer, but the device receiving the data might be another computer instead.

virtual printer n. A feature in many operating systems that allows printer output to be saved to a file until a printer becomes available.

virtual printer device driver n. See virtual device driver.

virtual private network n. 1. Nodes on a public network such as the Internet that communicate among themselves using encryption technology so that their messages are as safe from being intercepted and understood by unauthorized users as if the nodes were connected by private lines. 2. A WAN (wide area network) formed of permanent virtual circuits (PVCs) on another network, especially a network using technologies such as ATM or frame relay. Acronym: VPN. See also ATM (definition 1), frame relay, PVC.

virtual reality n. A simulated 3-D environment that a user can experience and manipulate as if it were physical. The user sees the environment on display screens, possibly mounted in a special pair of goggles. Special input devices, such as gloves or suits fitted with motion sensors, detect the user s actions. Acronym: VR.

Virtual Reality Modeling Language n. See VRML.

virtual real mode n. A feature of the Intel 80386 (SX and DX) and later microprocessors that allows them to emulate several 8086 (real-mode) environments at the same time. The microprocessor provides a set of virtual registers and virtual memory space to each virtual 8086 environment. A program running in a virtual 8086 environment is completely protected from other virtual 8086 environments in the system and behaves as if it had control of the entire system. Also called: V86 mode, virtual 8086 mode, virtual 86 mode. See also real mode.

virtual root n. The root directory that a user sees when connected to an Internet server, such as an HTTP or FTP server. The virtual root is actually a pointer to the physical root directory, which may be in a different location, such as on another server. The advantages of using a virtual root include being able to create a simple URL for the Internet site and to move the root directory without affecting the URL. Also called: v-root. See also pointer (definition 1), root directory, server (definition 2), URL.

virtual route n. See virtual circuit.

virtual screen n. An image area that extends beyond the dimensions of the physical screen on the monitor, allowing manipulation of large documents or of multiple documents that lie partially outside the normal screen view. See also monitor.

virtual server n. A virtual machine that resides on an HTTP server but has the appearance to the user of being a separate HTTP server. Several virtual servers can reside on one HTTP server, each capable of running its own programs and each with individualized access to input and peripheral devices. Each virtual server has its own domain name and IP address and appears to the user as an individual Web site. Some Internet service providers use virtual servers for those clients who want to use their own domain names. See also domain name, HTTP server (definition 2), IP address.

virtual storefront n. A company s point of presence on the Web, providing opportunities for online sales. Also called: electronic storefront.

virtual terminal n. See terminal emulation.

virtual timer device driver n. See virtual device driver.

virtual world n. 1. A 3-D modeled environment, often created in VRML, where a user can interact with the viewer to change variables. See also viewer, VRML. 2. An electronic environment that has no basis in the physical world. Multiuser dungeons (MUDs), talkers, and chat rooms are often considered virtual worlds. See also chat(definition 1), MUD, talker.

virus n. An intrusive program that infects computer files by inserting in those files copies of itself. The copies are usually executed when the file is loaded into memory, allowing the virus to infect still other files, and so on. Viruses often have damaging side effects sometimes intentionally, sometimes not. For example, some viruses can destroy a computer s hard disk or take up memory space that could otherwise be used by programs. See also Good Times virus, Trojan horse, worm.

virus signature n. A portion of unique computer code contained in a virus. Antivirus programs search for known virus signatures to identify infected programs and files. See also virus.

visible page n. In computer graphics, the image that is being displayed on the screen. Screen images are written into display memory in sections called pages, each of which contains one screen display.

Visio n. A software application offered by Microsoft that allows users to create diagrams and visual presentations in electronic form. Visio enables users to share ideas and concepts visually by using diagrams to augment written material in documents or by expanding visual elements in a public presentation. Microsoft acquired the Visio application in 1999, when it purchased Visio Corporation.

visit n. A session during which a person views one or more pages in a particular Web site.

visitor n. A person who views a Web page or Web site.

Visor n. A product line of handheld personal digital assistants (PDAs) developed by Handspring Corporation. Features include an address list, an appointments calendar, a to-do list, and memos. Visor also features a 68-pin Springboard socket that allows plug-ins of additional devices offered by Handspring. See also Springboard.

Visual Basic n. A trademarked name owned by Microsoft Corporation for a high-level, visual-programming version of Basic. Visual Basic was designed for building Windows-based applications. See also Basic, Visual Basic for Applications, Visual Basic, Scripting Edition, visual programming.

Visual Basic Editor n. An environment in which you write new and edit existing Visual Basic for Applications code and procedures. The Visual Basic Editor contains a complete debugging toolset for finding syntax, run-time, and logic problems in your code.

Visual Basic for Applications n. A macro-language version of Visual Basic that is used to program many Windows 9x applications and is included with several Microsoft applications. Acronym: VBA. See also macro language, Visual Basic.

Visual Basic Script n. See Visual Basic, Scripting Edition.

Visual Basic, Scripting Edition n. A subset of the Visual Basic programming language, optimized for Web-related programming. As with JavaScript, code for Visual Basic, Scripting Edition is embedded in HTML documents. This version is included with the Internet Explorer Web browser. Also called: VBScript, Visual Basic Script. See also Visual Basic for Applications.

Visual C++ n. A Microsoft application development system for the programming language C++ that runs under MS-DOS and Windows. Visual C++ is a visual programming environment. See also visual programming. Compare Visual Basic, Visual J++.

Visual Caf n. The Java-based suite of software development tools from Symantec Corporation. Visual Caf is available in several product packages. The Standard Edition, intended for beginning Java programmers, includes an integrated editor, debugger, and compiler, as well as a JavaBean library, wizards, and utilities. The Professional Edition provides a larger library of JavaBeans and more sophisticated tools for development and debugging. The Database Edition, as the name indicates, adds support for database functionality. The Enterprise Suite provides a high-end environment for development of enterprise applications. See also Java.

Visual FoxPro Database and Command Language n. A Microsoft product for developing database applications that includes a rich object-oriented programming language derived from the Xbase language.

Visual InterDev n. Microsoft s integrated development environment for Web applications. Visual InterDev includes tools for end-to-end (design through deployment) development, as well as integrated tools for database programming and design. The first version of Microsoft Visual InterDev was released in 1997.

visual interface n. See graphical user interface.

visualization n. A feature of an application that displays data in the form of a video image. For example, some databases can interpret and show data in the form of a two- or three-dimensional model.

Visual J++ n. Microsoft s Java visual programming environment, which can be used to create applets and applications in the Java language. See also applet, Java, Java applet, visual programming.

visual programming n. A method of programming using a programming environment or language in which basic program components can be selected through menu choices, buttons, icons, and other predetermined methods.

Visual SourceSafe n. A project-oriented version control system designed by Microsoft to manage software and Web site development. Visual SourceSafe stores files in a secure repository that provides easy access to authorized users and tracks all changes made to files. Visual SourceSafe works with any type of file produced by any development language, authoring tool, or application.

Visual Studio n. Microsoft s suite of software development tools for rapid development of business applications and components. Visual Studio is provided in two editions. The Professional Edition, for professional programmers, includes the Visual Basic and Visual C++ languages, Visual FoxPro for database development, Visual InterDev for Web development, and Visual J++ for Java development. The Enterprise Edition, for enterprise-level development, also includes Visual SourceSafe (a team-based source code control system) and the Developer Edition of Microsoft BackOffice Server.

Visual Studio .NET n. A development environment for creating XML Web services and applications on the Microsoft .NET platform. See also .NET, .NET My Services.

VLAN n. See virtual LAN.

VLB¹ adj. See VESA¹.

VLB² n. See VL bus.

VL bus n. Short for VESA local bus. A type of local bus architecture introduced by the Video Electronics Standards Association. The VL bus specification allows up to three VL bus slots to be built into a PC motherboard and allows for bus mastering (wherein intelligent adapter cards can do some processing independently of the CPU). A VL bus slot consists of a standard connector plus an additional 16-bit Micro Channel Architecture connector and must be built into the motherboard by the manufacturer. Standard connectors cannot simply be converted to VL bus slots. A non VL bus adapter card can be used in a VL bus slot, but it cannot use the local bus and so performs as it normally would in a non VL bus slot. Also called: VL local bus. See also local bus, PCI local bus.

VLF radiation n. Short for very-low-frequency radiation. Electromagnetic radiation (radio) at frequencies within the range of approximately 300 Hz to 30,000 Hz (30 kHz). Computer monitors emit this type of radiation. A voluntary standard, MPR II, regulates the amount of VLF radiation that a monitor can emit. See also MPR II.

VLIW n. Acronym for Very Long Instruction Word. An architecture that combines many simple instructions into a single long instruction word that uses different registers.

VL local bus n. See VL bus.

VLSI n. See very-large-scale integration.

VM n. Acronym for Virtual Machine. An operating system for IBM mainframes that provides virtual-machine capability. VM was developed by IBM customers and later taken over by IBM itself under the name OS/VM. See virtual memory. See also virtual machine.

VML n. Acronym for Vector Markup Language. An XML-based specification for the exchange, editing, and delivery of 2-D vector graphics on the Web. An application of XML (Extensible Markup Language), VML uses XML tags and Cascading Style Sheets to create and place vector graphics, such as circles and squares, in an XML or HTML document, such as a Web page. These graphics, which are rendered in the native operating system, can include color and are editable in a variety of graphics programs. See also Cascading Style Sheets, XML.

VoATM n. Short for Voice over Asynchronous Transfer Mode. The transmission of voice and other telephony over an ATM network. See also ATM, VoFR, VoIP.

VoFR n. Short for Voice over Frame Relay. Voice transmission over a frame relay network. See also frame relay, VoATM, VoIP.

voice answer back n. The use of sound-recorded messages by a computer in responding to commands or queries. Acronym: VAB.

voice-capable modem n. A modem that can support voice messaging applications along with its data-handling functions.

voice chat n. A feature offered by Internet service providers (ISPs) that allows users to converse with each other directly through an Internet connection. See also Internet telephone.

voice coil n. A device that moves a disk drive actuator arm using electromagnetism. It works more quickly than a stepper motor. See also actuator. Compare stepper motor.

voice-grade channel n. A communications channel, such as a telephone line, with an audio bandwidth of 300 to 3000 Hz, suitable for carrying speech. A voice-grade channel can also be used for transmitting facsimile, analog, and digital information at rates up to 33 kilobits per second (Kbps).

voice input n. Spoken instructions that a computer translates into executable commands using speech recognition technology or that are embedded into documents with the aid of a microphone. See also speech recognition.

voice mail n. A system that records and stores telephone messages in a computer s memory. Unlike a simple answering machine, a voice mail system has separate mailboxes for multiple users, each of whom can copy, store, or redistribute messages.

voice messaging n. A system that sends and receives messages in the form of sound recordings.

voice modem n. A modulation/demodulation device that supports a switch to change between telephony and data transmission modes. Such a device might contain a built-in loudspeaker and microphone for voice communication, but more often it uses the computer s sound card. See also modem, sound card, telephony.

voice navigation n. The use of spoken commands to control a Web browser. Voice navigation is a feature of some plug-in applications that embellish Web browsers to allow the user to navigate the Web by means of his or her voice. See also Web browser.

voice-net n. A term used on the Internet to refer to the telephone system, often preceding the user s telephone number in an e-mail signature.

voice output n. See speech synthesis.

Voice over Asynchronous Transfer Mode n. See VoATM.

Voice over Frame Relay n. See VoFR.

Voice over IP n. See VoIP.

voice recognition n. The capability of a computer to understand the spoken word for the purpose of receiving commands and data input from the speaker. Systems that can recognize limited vocabularies as spoken by specific individuals have been developed, but developing a system that deals with a variety of speech patterns and accents, as well as with the various ways in which a request or a statement can be made, is more difficult, although advances are being made in this area. Also called: speech recognition. See also artificial intelligence, dictation software, neural network.

voice synthesis n. See speech synthesis.

VoIP n. Acronym for Voice over IP. The use of the Internet Protocol (IP) for transmitting voice communications. VoIP delivers digitized audio in packet form and can be used for transmitting over intranets, extranets, and the Internet. It is essentially an inexpensive alternative to traditional telephone communication over the circuit-switched Public Switched Telephone Network (PSTN). VoIP covers computer-to-computer, computer-to-telephone, and telephone-based communications. For the sake of compatibility and interoperability, a group called the VoIP Forum promotes product development based on the ITU-T H.323 standard for transmission of multimedia over the Internet. Also called: Internet telephony. See also H.323.

volatile memory n. 1. Memory, such as RAM, that loses its data when the power is shut off. Compare nonvolatile memory. 2. Memory used by a program that can change independently of the program, such as memory shared by another program or by an interrupt service routine.

volt n. The unit used to measure potential difference or electromotive force. One volt is defined as the potential across which 1 coulomb of charge will do 1 joule of work, or the potential generated by 1 ampere of current flowing through 1 ohm of resistance. See also electromotive force.

voltage n. See electromotive force.

voltage regulator n. A circuit or circuit component that maintains a constant output voltage despite variations in input voltage.

volts alternating current n. The measure of the peak-to-peak voltage swing of an electrical signal. Acronym: VAC.

volume n. 1. A disk or tape that stores computer data. Sometimes, large hard disks are divided into several volumes, each of which is treated as a separate disk. 2. The loudness of an audio signal.

volume label n. A name for a disk or tape. MS-DOS systems, which seldom use disk names except in directory listings, use the term volume label. Apple Macintosh systems, which often refer to disks by name, use the term volume name.

volume name n. See volume label.

volume reference number n. See volume serial number.

volume serial number n. The optional identifying volume number of a disk or tape. MS-DOS systems use the term volume serial number. Apple Macintosh systems use the term volume reference number. A volume serial number is not the same as a volume label or volume name. Compare volume label.

VON n. Acronym for voice on the net. A broad category of hardware and software technology for real-time voice and video transmission over the Internet. The term was coined by Jeff Pulver, who formed a group called the VON Coalition, which opposes regulation of VON technology and promotes VON to the public.

von Neumann architecture n. The most common structure for computer systems, attributed to the mathematician John von Neumann. It uses the concept of a program that can be permanently stored in a computer and manipulated or made self-modifying through machine-based instructions. Sequential processing is characteristic of von Neumann architecture. Parallel architectures have evolved to improve on the encumbrances of sequential instructions. See also parallel computer.

von Neumann bottleneck n. Competition between data and instructions for CPU time. Mathematician John von Neumann was the first to show that a computer based on architecture linking a single processor with memory will actually spend more time retrieving data from memory than processing it. The bottleneck arises when the processor has to trade off between executing a large number of instructions per second and reading in a large amount of data in the same time. See also CPU.

VPD n. Acronym for virtual printer device driver. See virtual device driver.

VPN n. See virtual private network.

VR n. See virtual reality.

VRAM n. See video RAM.

VRC n. Acronym for vertical redundancy check. A method for checking the accuracy of transmitted data. VRC generates an extra bit (parity bit) for each character transmitted. The parity bit indicates whether the character contains an odd or an even number of 1 bits. If its value does not match the type of the character, that character is assumed to be incorrectly transmitted. See also parity. Compare LRC.

VRML n. Acronym for Virtual Reality Modeling Language. A scene description language for creating 3-D interactive Web graphics similar to those found in some video games, allowing the user to move around within a graphic image and interact with objects. VRML, a subset of Silicon Graphics Inventor File Format (ASCII), was created by Mark Pesce and Tony Parisi in 1994. VRML files can be created in a text editor, although CAD packages, modeling and animation packages, and VRML authoring software are the tools preferred by most VRML authors. VRML files reside on an HTTP server; links to these files can be embedded in HTML documents, or users can access the VRML files directly. To view VRML Web pages, users need a VRML-enabled browser or a VRML plug-in for Internet Explorer or Netscape Navigator. See also 3-D graphic, HTML document, HTTP server (definition 1).

v-root n. See virtual root.

V series n. The series of ITU-T (formerly CCITT) recommendations relating to modems and modem communications over the public phone system, including signaling, coding, and circuit characteristics. See the table.

Table V.1 Recommendations in the V Series for Modem Communications.

Recommendation Number	What It Covers
V.17	14,000-bps two-wire modems used for facsimile applications
V.21	300-bps modems used with dial-up lines; full-duplex transmission; not the same as Bell 103 (in North America)
V.22	1200-bps modems used with dial-up and leased lines; full-duplex transmission; not the same as Bell 212A (in North America)
V.22bis	2400-bps modems used with dial-up and leased lines; full-duplex transmission
V.23	600/1200-bps synchronous or asynchronous modems used with dial-up and leased lines; half-duplex transmission
V.26	2400-bps modems used with four-wire leased lines; full-duplex transmission
V.26bis	1200/2400-bps modems used with dial-up lines; full-duplex transmission
V.26ter	2400-bps modems used with dial-up and two-wire leased lines; DPSK modulation; fallback to 1200 bps; echo canceling to remove phone-line echo; full-duplex transmission
V.27	4800-bps modems used with leased lines; manual equalizer; full-duplex transmission
V.27bis	2400/4800-bps modems used with leased lines; automatic equalizer; full-duplex transmission
V.27ter	2400/4800-bps modems used with dial-up lines; full-duplex transmission
V.29	9600-bps modems used with point-to-point leased circuits; half-duplex transmission or full-duplex transmission
V.32	9600-bps modems used with dial-up lines; echo canceling to remove phone-line echo; full-duplex transmission
V.32bis	4800/7200/9600/12,000/14,400-bps modems used with dial-up lines; echo canceling; full-duplex transmission
V.33	12,000/14,400-bps modems used with four-wire leased lines; synchronous; QAM modulation; time-division multiplexing; full-duplex transmission
V.34	28,800-bps modems; full-duplex transmission
V.35	Group band modems, which combine the bandwidth of more than one telephone circuit
V.54	Operation of loop test devices in modems
V.56	Network transmission model for evaluating modem performance over standard voice-grade telephone connections
V.56bis	Network transmission model for evaluating modem performance over two-wire voice-grade connections
V.56ter	Network transmission model for evaluating modem performance over two-wire, 4-kilohertz duplex modems
V.61	4800-bps modems operating at voice plus data rate or 14,000-bps modems operating at data-only rate over standard switched telephone circuits or on point-to-point, two-wire phone circuits

V-sync n. See vertical bandwidth.

VT-52, VT-100, VT-200 n. A popular set of control codes used in terminals with those model numbers that were originally manufactured by Digital Equipment Corporation. Appropriate software can enable a microcomputer to use these codes to emulate such terminals.

VTD n. Acronym for virtual timer device driver. See virtual device driver.

Vulcan death grip n. A warm boot by pressing the Alt+Crl+Delete keys. The name is a reference from Star Trek. See also three-finger salute, warm boot.

V x D n. See virtual device driver.