T

T

T prefix See tera-.

T1 or T-1 n. A high-speed communications line that can handle digital communications and Internet access at the rate 1.544 Mbps (megabits per second). Although originally designed by AT&T to carry multiple voice calls over standard twisted-pair telephone wiring, this high-bandwidth telephone line can also transmit text and images. T1 speed is attained through multiplexing 24 separate 64 Kbps channels into a single data stream. T1 lines are commonly used by larger organizations for Internet connectivity. Also called: T-1 carrier. See also T-carrier. Compare fractional T1, T2, T3, T4.

T.120 standard n. A family of International Telecommunications Union (ITU) specifications for multipoint data communications services within computer applications, such as conferencing and multipoint file transfer.

T2 or T-2 n. A T-carrier that can handle 6.312 Mbps (megabits per second) or 96 voice channels. See also T-carrier. Compare T1, T3, T4.

T3 or T-3 n. A T-carrier that can handle 44.736 Mbps (megabits per second) or 672 voice channels. See also T-carrier. Compare T1, T2, T4.

T4 or T-4 n. A T-carrier that can handle 274.176 Mbps (megabits per second) or 4032 voice channels. See also T-carrier. Compare T1, T2, T3.

TA n. See terminal adapter.

tab character n. A character used to align lines and columns on screen and in print. Although a tab is visually indistinguishable from a series of blank spaces in most programs, the tab character and the space character are different to a computer. A tab is a single character and therefore can be added, deleted, or overtyped with a single keystroke. The ASCII coding scheme includes two codes for tab characters: a horizontal tab for spacing across the screen or page and a vertical tab for spacing down the screen or page. See also Tab key.

Tab key n. A key, often labeled with both a left-pointing and a right-pointing arrow, that traditionally (as in word processing) is used to insert tab characters into a document. In other applications, such as menu-driven programs, the Tab key is often used to move the on-screen highlight from place to place. Many database and spreadsheet programs allow the user to press the Tab key to move around within a record or between cells. The word tab is short for tabulator, which was the name given to this key on typewriters, where it was used in creating tables. See also tab character.

table n. 1. In programming, a data structure usually consisting of a list of entries, each entry being identified by a unique key and containing a set of related values. A table is often implemented as an array of records, a linked list, or (in more primitive languages) several arrays of different data types, all using a common indexing scheme. See also array, list, record. 2. In relational databases, a data structure characterized by rows and columns, with data occupying or potentially occupying each cell formed by a row-column intersection. The table is the underlying structure of a relation. See also relational database. 3. In word processing, desktop publishing, and in HTML documents, a block of text formatted in aligned rows and columns.

table lookup n. The process of using a known value to search for data in a previously constructed table of values for example, using a purchase price to search a tax table for the appropriate sales tax. See also lookup.

tablet n. See graphics tablet.

Tablet PC n. A touch-sensitive computer screen tablet designed by Microsoft for the entry of handwritten text using a stylus or digital pen. The Tablet PC runs Windows applications and can function as a primary personal computer as well as a note-taking device.

tabulate vb. 1. To total a row or column of numbers. 2. To arrange information in table form.

TACACS n. Acronym for Terminal Access Controller Access Control System. A network access technique in which users log into a single centralized server that contains a database of authorized accounts. After the access server authenticates the user, it forwards the login information to the data server requested by the user. See also authentication, server (definition 2).

tag n. 1. In programming, one or more characters containing information about a file, record type, or other structure. 2. In certain types of data files, a key or an address that identifies a record and its storage location in another file. See also tag sort. 3. In markup languages such as SGML and HTML, a code that identifies an element in a document, such as a heading or a paragraph, for the purposes of formatting, indexing, and linking information in the document. In both SGML and HTML, a tag is generally a pair of angle brackets that contain one or more letters and numbers. Usually one pair of angle brackets is placed before an element, and another pair is placed after, to indicate where the element begins and ends. For example, in HTML, <I>hello world</I> indicates that the phrase hello world should be italicized. See also <>, element, emotag, HTML, SGML. 4. An early-generation raster graphics format used for Macintosh Ready, Set, Go programs and Letraset s ImageStudio. See also raster graphics.

Tagged Image File Format n. See TIFF.

tag sort n. A sort performed on one or several key fields for the purpose of establishing the order of their associated records. Also called: key sort.

tag switching n. A multilayer Internet switching technology developed by Cisco Systems that integrates routing and switching.

talk¹ n. The UNIX command that, when followed by another user s name and address, is used to generate a request for a synchronous chat session on the Internet. See also chat¹ (definition 1).

talk² vb. See chat².

talker n. An Internet-based synchronous communication mechanism most commonly used to support multiuser chat functions. Such systems typically provide specific commands for movement through separate rooms, or chat areas, and allow users to communicate with other users in real time through text messages, indicate simple gestures, use a bulletin board system (BBS) for posting comments, and send internal e-mail. See also BBS (definition 1), chat (definition 1).

talk. newsgroups n. Usenet newsgroups that are part of the talk. hierarchy and have the prefix talk. as part of their names. These newsgroups are devoted to debate and discussion of controversial topics. Talk. newsgroups are one of the seven original Usenet newsgroup hierarchies. The other six are comp., misc., news., rec., sci., and soc. See also newsgroup, traditional newsgroup hierarchy, Usenet.

tandem processors n. Multiple processors wired so that the failure of one processor transfers central processing unit (CPU) operation to another processor. Using tandem processors is part of the strategy for implementing fault-tolerant computer systems. See also central processing unit.

TANSTAAFL n. Acronym for There ain t no such thing as a free lunch. An expression used on the Internet in e-mail, chat sessions, mailing lists, newsgroups, and other online forums; derived from The Moon Is a Harsh Mistress, a science-fiction classic by Robert A. Heinlein. See also chat¹ (definition 1), e-mail¹ (definition 1), mailing list, newsgroup.

tap¹ n. A device that can be attached to an Ethernet bus to enable a computer to be connected.

tap² vb. To use a stylus to quickly touch a device screen to perform an activity. Tapping is analogous to clicking with a mouse.

tap and hold vb. To hold a stylus on a device screen to open a pop-up or shortcut menu. Analogous to right-clicking with a mouse.

tape n. 1. A thin strip of polyester film coated with magnetic material that permits the recording of data. Because tape is a continuous length of data storage material and because the read/write head cannot jump to a desired point on the tape without the tape first being advanced to that point, tape must be read or written sequentially, not randomly (as can be done on a floppy disk or a hard disk). 2. A storage medium consisting of a thin strip of paper used to store information in the form of sequences of punched holes, chemical impregnation, or magnetic ink imprinting.

tape cartridge n. A module that resembles an audio cassette and contains magnetic tape that can be written on and read from by a tape drive. Tape cartridges are primarily used to back up hard disks. See also tape (definition 1).

tape drive n. A device for reading and writing tapes. See also tape (definition 1).

tape dump n. The process of simply printing the data contained on a tape cartridge without performing any report formatting. See also tape cartridge.

tape tree n. A means of audiotape distribution, used in Usenet music newsgroups and mailing lists, in which a recording is copied and sent to a number of branch participants, who in turn send copies to their children, or leaves. See also branch (definition 1), child (definition 2), leaf, tree structure. Compare vine.

TAPI n. Acronym for Telephony Application Programming Interface. In the Windows Open Systems Architecture (WOSA), a programming interface that gives Windows client applications access to a server s voice services. TAPI facilitates interoperability between personal computers and telephone equipment. Also called: Telephony API. See also application programming interface, WOSA. Compare TSAPI.

.tar n. The file extension that identifies uncompressed UNIX archives in the format produced by the tar program.

tar¹ n. Acronym for tape archive. A UNIX utility for making a single file out of a set of files that a user wishes to store together. The resulting file has the extension .tar. Unlike PKZIP, tar does not compress files, so compress or gzip is usually run on the .tar file to produce a file with extensions .tar.gz or .tar.Z. See also compress¹, gzip, PKZIP. Compare untar¹.

tar² vb. To make a single file out of a set of files using the tar utility. See also compress¹, PKZIP. Compare untar¹.

target n. Loosely, the objective of a computer command or operation. Examples are a computer that is to run a program translated for its use, a foreign language (for another computer) into which a program is to be translated, or a group of people for whom a particular product is designed. In MS-DOS usage, the target is often the disk referred to by prompts in a copy operation (for example, insert target diskette ). In terms of the SCSI (small computer system interface) connection, the target is the device that receives commands. See also SCSI, target computer, target disk, target language.

target computer n. The computer that receives data from a communications device, a hardware add-in, or a software package.

target disk n. The disk to which data is to be written, as in a copy operation. See also target. Compare source disk.

target language n. The language into which source code is compiled or assembled. See also assembler, compiler (definition 2), cross-compiler.

task n. A stand-alone application or a subprogram that is run as an independent entity.

taskbar n. A graphic toolbar used in Windows 9x, Windows CE, Windows NT, and Windows 2000 to select, via the mouse, one of a number of active applications. See also task button, toolbar.

task button n. In Windows 9x, Windows CE, Windows NT, and Windows 2000, a button that appears on the taskbar on the screen when an application is run. By clicking on the button, the user can switch from another application to the application corresponding to the button. See also taskbar.

task management n. The operating-system process of tracking the progress of and providing necessary resources for separate tasks that are running on a computer, especially in a multitasking environment.

task swapping n. The process of switching from one application to another by saving the data for the application presently running in the foreground to a storage device and loading the other application. See also foreground(definition 2), task, task switching.

task switching n. The act of moving from one program to another without shutting down the first program. Task switching is a single act, as compared to multitasking, in which the central processing unit rapidly switches back and forth between two or more programs. See also task, task swapping. Compare multitasking.

TB n. See terabyte.

T-carrier n. A long-distance, digital communications line provided by a common carrier. Multiplexers at either end merge several voice channels and digital data streams for transmission and separate them when received. T-carrier service, introduced by AT&T in 1993, is defined at several capacity levels: T1, T2, T3, and T4. In addition to voice communication, T-carriers are used for Internet connectivity. See also T1, T2, T3, T4.

TCB n. Acronym for Trusted Computing Base. The complete set of security mechanisms that create security on a network. The TCB includes all the hardware, software, and firmware components that are responsible for system security.

Tcl/Tk n. Acronym for Tool Command Language/Tool Kit. A programming system that includes a scripting language (Tcl) and a graphical user interface toolkit (Tk). The Tcl language issues commands to interactive programs, such as text editors, debuggers, and shells, which tie together complex data structures into scripts. See also graphical user interface, script, scripting language.

TCM n. See trellis-coded modulation.

TCO n. See total cost of ownership.

TCP n. Acronym for Transmission Control Protocol. The protocol within TCP/IP that governs the breakup of data messages into packets to be sent via IP (Internet Protocol), and the reassembly and verification of the complete messages from packets received by IP. A connection-oriented, reliable protocol (reliable in the sense of ensuring error-free delivery), TCP corresponds to the transport layer in the ISO/OSI reference model. See also ISO/OSI reference model, packet, TCP/IP. Compare UDP.

TCP/IP n. Acronym for Transmission Control Protocol/Internet Protocol. A protocol suite (or set of protocols) developed by the U.S. Department of Defense for communications over interconnected, sometimes dissimilar, networks. It is built into the UNIX system and has become the de facto standard for data transmission over networks, including the Internet.

TCP/IP reference model n. A networking model designed around the concept of internetworking the exchange of information among different networks, often built on different architectures. The TCP/IP reference model, often called the Internet reference model, consists of four layers, the most distinctive of which is the internetwork that deals with routing messages and that has no equivalent in the ISO/OSI reference model or the SNA model. Compare ISO/OSI reference model, SNA.

TCP/IP stack n. The set of TCP/IP protocols. See also protocol stack, TCP/IP.

TDM n. See time-division multiplexing.

TDMA n. Short for Time Division Multiple Access. A multiplexing technology used to divide a single cellular phone channel into multiple subchannels. TDMA works by allocating separate time slots to each user. It is implemented in D-AMPS (Digital Advanced Mobile Phone Service), which relies on TDMA to divide each of the 30 analog AMPS channels into 3 separate subchannels, and GSM (Global System for Mobile Communications). See also D-AMPS, Global System for Mobile Communications. Compare AMPS, FDMA.

team Web site n. See SharePoint team Web site.

Teardrop attack n. An Internet-based attack that breaks a message into a series of IP fragments with overlapping offset fields. When these fragments are reassembled at their destination, the fields don t match, causing the system to hang, reboot, or crash.

tearing n. A visual artifact produced when the screen refresh rate is out of sync with an application s frame rate. The top portion of one frame is displayed at the same time as the bottom portion of another frame, with a discernible tear between the two partial images.

tear-off adj. Capable of being dragged from an original position in a graphical user interface and placed where the user desires. For example, many graphics applications feature tear-off menus of tool palettes that can be dragged to locations other than the menu bar.

techie n. A technically oriented person. Typically, a techie is the person on whom a user calls when something breaks or the user cannot understand a technical problem. A techie may be an engineer or a technician, but not all engineers are techies. See also guru.

technical author n. See tech writer.

technobabble n. Language that includes incomprehensible technical terms and jargon. In ordinary conversation, many of the words in this dictionary might be considered technobabble.

technology n. The application of science and engineering to the development of machines and procedures in order to enhance or improve human conditions, or at least to improve human efficiency in some respect. See also high tech.

technophile n. Someone who is enthusiastic about emerging technology. Compare computerphile.

technophobe n. A person who is afraid of or dislikes technological advances, especially computers. See also Luddite. Compare technophile.

tech writer n. Short for technical writer. One who writes the documentation material for a hardware or software product. Also called: technical author. See also documentation.

telco n. Short for telephone company. A term generally used in reference to a telephone company s provision of Internet services.

telecom closet n. See wiring closet.

telecommunications n. The transmission and reception of information of any type, including data, television pictures, sound, and facsimiles, using electrical or optical signals sent over wires or fibers or through the air.

telecommunications closet n. See wiring closet.

telecommute vb. To work in one location (often at home) and communicate with a main office at a different location through a personal computer equipped with a modem and communications software.

telecommuter n. A member of the workforce who conducts business outside the traditional office setting, collaborating with business associates and colleagues through communications and computer technologies. Some workers telecommute full-time; others part-time. The telecommuting ranks include self-employed home workers, small-business entrepreneurs, and employees of large corporations or organizations. See also distributed workplace, SOHO.

teleconferencing n. The use of audio, video, or computer equipment linked through a communications system to enable geographically separated individuals to participate in a meeting or discussion. See also video conferencing.

telecopy vb. See fax.

telematics n. In communications technology, the linking of computers and telecommunications. Telematics technology is becoming standard in the automotive industry, with dashboard navigation systems, roadside assistance, entertainment, Internet, and cellular services available in vehicles.

telephony n. Telephone technology voice, fax, or modem transmissions based on either the conversion of sound into electrical signals or wireless communication via radio waves.

Telephony API n. See TAPI.

telephony device n. A mechanism designed to translate sound into electrical signals, transmit them, and then convert them back to sound.

Telephony Service Provider n. A modem driver that enables access to vendor-specific equipment through a standard device driver interface. Acronym: TSP. See also Telephony Service Provider Interface.

Telephony Service Provider Interface n. The external interface of a service provider to be implemented by vendors of telephony equipment. A telephony service provider accesses vendor-specific equipment through a standard device driver interface. Installing a service provider allows Windows CE based applications that use elements of telephony to access the corresponding telephony equipment. Acronym: TSPI. See also Telephony Service Provider.

teleprocess vb. To use a terminal or computer and communications equipment to access computers and computer files located elsewhere. Teleprocess is a term originated by IBM. See also distributed processing, remote access.

teleprocessing monitor n. See TP monitor.

Telescript n. A communications-oriented programming language, released in 1994 by General Magic, that was designed to address the need for cross-platform, network-independent messaging and abstraction of complex network protocols. See also communications protocol.

teletext n. All-text information broadcast by a television station to a subscriber s television set.

Teletype n. The Teletype Corporation, developer of the teletypewriter (TTY) and various other printers used with computers and communications systems. See also TTY.

teletype mode n. A mode of operation in which a computer or an application limits its actions to those characteristic of a teletypewriter (TTY). On the display, for example, teletype mode means that only alphanumeric characters can be shown, and they are simply typed on the screen, one letter after the other, and cannot be placed in any desired position. See also Teletype, TTY.

teletypewriter n. See TTY.

teleworker n. A businessperson who substitutes information technologies for work-related travel. Teleworkers include home-based and small business workers who use computer and communications technologies to interact with customers and/or colleagues. See also distributed workplace, SOHO.

telnet¹ n. 1. A client program that implements the Telnet protocol. 2. A protocol in the TCP/IP suite that enables individuals to log on to and use a remote computer as if they were sitting at a terminal directly connected to the machine.

telnet² vb. To access a remote computer over the Internet using the Telnet protocol. See also telnet¹.

Telnet n. A protocol that enables an Internet user to log on to and enter commands on a remote computer linked to the Internet, as if the user were using a text-based terminal directly attached to that computer. Telnet is part of the TCP/IP suite of protocols.

template n. 1. In an application package, an overlay for the keyboard that identifies special keys and key combinations. 2. In image processing, a pattern that can be used to identify or match a scanned image. 3. In spreadsheet programs, a predesigned spreadsheet that contains formulas, labels, and other elements. 4. In MS-DOS, a small portion of memory that holds the most recently typed MS-DOS command. 5. In word processing and desktop publishing programs, a predesigned document that contains formatting and, in many cases, generic text.

temporary file n. A file created either in memory or on disk, by the operating system or some other program, to be used during a session and then discarded. Also called: temp file. See also scratch¹.

temporary storage n. A region in memory or on a storage device that is temporarily allocated for use in storing intermediate data in a computational, sorting, or transfer operation.

ten s complement n. A number in the base-10 system that is the true complement of another number and is derived either by subtracting each digit from 1 less than the base and adding 1 to the result or by subtracting each number from the next higher power of the base. For example, the ten s complement of 25 is 75, and it can be derived either by subtracting each digit from 9, which is 1 less than the base (9 2 = 7, 9 5 = 4) and then adding 1 (74 + 1 = 75) or by subtracting 25 from the next higher power of 10, which is 100 (100 25 = 75). See also complement. Compare nine s complement.

tera- prefix A prefix meaning 10¹²: 1 trillion in the American numbering system, 1 million million in British numbering.Abbreviation: T. See also terabyte.

terabyte n. A measurement used for high-capacity data storage. One terabyte equals 2⁴⁰, or 1,099,511,627,776, bytes, although it is commonly interpreted as simply one trillion bytes.Abbreviation: TB.

teraflops n. One trillion floating-point operations (FLOPS) per second. Teraflops serves as a benchmark for larger computers that measures the number of floating-point operations they can perform in a set amount of time. Also called: TFLOPS. See also FLOPS.

terminal n. 1. In networking, a device consisting of a video adapter, a monitor, and a keyboard. The adapter and monitor and, sometimes, the keyboard are typically combined in a single unit. A terminal does little or no computer processing on its own; instead, it is connected to a computer with a communications link over a cable. Terminals are used primarily in multiuser systems and today are not often found on single-user personal computers. See also dumb terminal, smart terminal, terminal emulation. 2. In electronics, a point that can be physically linked to something else, usually by a wire, to form an electrical connection.

Terminal n. An application that provides command-line access to the Mac OS X UNIX core. The Terminal command-line environment allows UNIX functions from within Mac OS X.

Terminal Access Controller Access Control System n. See TACACS.

terminal adapter n. The correct name for an ISDN modem, which connects a PC to an ISDN line but does not modulate or demodulate signals as a typical modem does.

terminal emulation n. The imitation of a terminal by using software that conforms to a standard, such as the ANSI standard for terminal emulation. Terminal-emulation software is used to make a microcomputer act as if it were a particular type of terminal while it is communicating with another computer, such as a mainframe. See also VT-52, VT-100, VT-200.

terminal server n. In a LAN (local area network), a computer or a controller that allows terminals, microcomputers, and other devices to connect to a network or host computer, or to devices attached to that particular computer. See the illustration. See also controller, LAN, microcomputer, terminal.

Terminal server.

terminal session n. The period of time spent actively using a terminal. See also session.

terminal strip n. A usually long and narrow assembly containing one or more electrical connectors. Commonly, terminal strips consist of screws on which bare wires are wrapped before the screws are tightened; for example, some consumer-grade stereo receiver/amplifiers incorporate a set of terminal strips on the rear panel for attaching speaker wires to the unit.

terminate vb. 1. With reference to software, to end a process or program. Abnormal termination occurs in response to user intervention or because of a hardware or software error. 2. With reference to hardware, to install a plug, jack, or other connector at the end of a wire or cable.

terminate-and-stay-resident program n. See TSR.

terminator n. 1. A character that indicates the end of a string, such as the null character in an ASCIIZ string. See also ASCII, ASCIIZ string. 2. An item of hardware that must be installed in the last device in a daisy chain or bus network, such as Ethernet or SCSI. The terminator caps the end of a cable in a bus network in order to keep signals from bouncing back along the line. See also terminator cap.

terminator cap n. A special connector that must be attached to each end of an Ethernet bus. If one or both terminator caps are missing, the Ethernet network will not work.

ternary adj. In programming, of, pertaining to, or characteristic of an element with three possible values, a condition that has three possible states, or a base-3 number system. Compare binary¹, unary.

tessellate vb. To break an image into small, square regions for processing or output.

test vb. To check program correctness by trying out various sequences and input values. See also debug, test data.

test automation software n. A program that automatically enters a predetermined set of characters or user commands in order to test new or modified versions of software applications.

test data n. A set of values used to test proper functioning of a program. Reasons for choosing particular test data include verifying known output (anticipated output) and pushing boundary conditions that might cause the program to fail.

test post n. A newsgroup article that contains no actual message but is used simply as a means of checking the connection. See also article, newsgroup.

TeX or T_EX n. A text-formatting software system created by mathematician and computer scientist Donald Knuth for producing typeset-quality scientific, mathematical, or other complex technical documents from plain ASCII text input. Implementations of TeX for UNIX systems, MS-DOS and Windows, and the Apple Macintosh are available free over the Internet (ftp://ftp.tex.ac.uk/tex-archive/) or in commercial distributions (which often include enhancements). Commands in the input file produce format elements and special symbols; for example, ${\pi}r^2$ produces the expression pr ². TeX is extensible through macros, and macro files are available for a wide variety of applications. See also LaTeX.

Texas Instruments Graphics Architecture n. See TIGA.

texel n. A single element in a texture. When a texture has been applied to an object, the texels rarely correspond to pixels on the screen. Applications can use texture filtering to control how texels are sampled and interpolated to pixels.

text n. 1. Data that consists of characters representing the words and symbols of human speech; usually, characters coded according to the ASCII standard, which assigns numeric values to numbers, letters, and certain symbols. 2. In word processing and desktop publishing, the main portion of a document, as opposed to headlines, tables, figures, footnotes, and other elements.

text box n. In a dialog box or HTML form, a box in which the user may enter text.

TextEdit n. A standard set of routines in the Macintosh operating system that are available to programs for controlling the way text is displayed. See also Toolbox.

text editor n. See editor.

text entry n. The inputting of text characters by means of a keyboard.

text file n. A file composed of text characters. A text file can be a word-processing file or a plain ASCII file encoded in a format practically all computers can use. See also ASCII file, text (definition 1).

text mode n. A display mode in which the monitor can display letters, numbers, and other text characters but no graphical images or WYSIWYG ( what-you-see-is-what-you-get ) character formatting (italics, superscript, and so on). Also called: alphanumeric mode, character mode. Compare graphics mode.

text-only file n. See ASCII file.

text-to-speech n. The conversion of text-based data into voice output by speech synthesis devices to allow users to gain access to information by telephone or to allow blind or illiterate people to use computers.

Text-to-Speech n. See TTS (definition 1).

texture n. In computer graphics, shading or other attributes added to the surface of a graphical image to give it the illusion of a physical substance. For example, a surface could be made to appear reflective to simulate metal or glass, or a scanned image of wood grain could be applied to a shape intended to simulate an object made of wood.

texture mapping n. In 3-D graphics, the process of adding detail to an object by creating a picture or a pattern that can be wrapped around the object. For example, a texture map of stones might be wrapped around a pyramid shape to create a realistic image. Texture mapping can also account for changes in perspective as the picture is wrapped around the shape. The technique is valued in 3-D graphics because it enables creation of detailed images without the performance degradation that can result from the computation required to manipulate images created with large numbers of polygons.

TFLOPS n. See teraflops.

TFT n. Acronym for thin film transistor. A transistor created using thin film methodology. See also active matrix display, thin film, transistor.

TFT display n. See active matrix display.

TFT LCD n. Acronym for thin film transistor liquid crystal display. See active matrix display.

TFTP n. See Trivial File Transfer Protocol.

TGA n. 1. Short for Targa. A raster graphics file format from Truevision, Inc., that handles 16-, 24-, and 32-bit color. See also 16-bit color, 24-bit color, 32-bit color, raster graphics, video graphics board. 2. The brand name of a series of high-resolution video graphics boards.

theme n. 1. A set of visual elements that provide a unified look for your computer desktop. A theme determines the look of the various graphic elements of your desktop, such as the windows, icons, fonts, colors, and the background and screen saver pictures. It can also define sounds associated with events, such as opening or closing a program. 2. A set of coordinated graphic elements applied to a document or Web page, or across all pages in a Web site. Themes can consist of designs and color schemes for fonts, link bars, and other page elements.

The Microsoft Network n. See MSN.

thermal printer n. A nonimpact printer that uses heat to generate an image on specially treated paper. The printer uses pins to produce an image, but rather than striking the pins against a ribbon to mark the paper as does a wire-pin dot-matrix printer, it heats the pins and brings them into gentle contact with the paper. The special coating on the paper discolors when it is heated.

thermal transfer printer n. See thermal wax-transfer printer.

thermal wax printer n. See thermal wax-transfer printer.

thermal wax-transfer printer n. A special type of nonimpact printer that uses heat to melt colored wax onto paper to create an image. Like a standard thermal printer, it uses pins to apply the heat. Rather than making contact with coated paper, however, the pins touch a wide ribbon saturated with different colored waxes. The wax melts under the pins and adheres to the paper.

thesaurus n. 1. A book of words and their synonyms. 2. In microcomputer applications, both a file of synonyms stored on disk and the program used to search the file.

The World Public Access UNIX n. One of the oldest public access Internet service providers, based in Boston. In 1990, The World began offering full dial-up Internet access to the public. Other services include World Wide Web access, Usenet, SLIP/PPP support, telnet, FTP, IRC, Gopher, and e-mail. In 1995, The World began supporting local dial-up access via UUNET. See also ISP.

thick Ethernet n. See 10Base5.

thick film adj. A term describing a method used in the manufacture of integrated circuits. Thick film technology uses a stencil-like technique called photosilkscreening to deposit multiple layers of special inks or pastes on a ceramic substrate. The inks or pastes can be conducting, insulating, or resistive. The passive components (wires, resistors, and capacitors) of the integrated circuits are formed by depositing a series of films of different characteristics and patterns. Compare thin film.

ThickNet n. See 10Base5.

ThickWire n. See 10Base5.

thimble n. A type element, similar to a daisy wheel, that bears a full character set, with each character on a separate type bar. As with a daisy wheel, the spokes, or type bars, radiate out from a central hub. On a thimble print element, however, each type bar is bent 90 degrees at its halfway point, so the type bars stick straight up with the type facing away from the hub. See also thimble printer. Compare daisy wheel, daisy-wheel printer.

thimble printer n. A printer that uses a thimble print element, best known in a line of printers from NEC. Because these printers use fully formed characters like those on a typewriter, they generate letter-quality output that is indistinguishable from that of a typewriter. This includes the slight impression created by the type hitting the paper hard through the ribbon, which distinguishes this type of printout from that of laser printers. See also thimble. Compare daisy-wheel printer.

thin client n. A software layer of a small client for a centrally managed, network terminal. The thin client allows the user access to server-hosted applications and data.

thin Ethernet n. See 10Base2.

thin film adj. A method used in the fabrication of integrated circuits. Thin film technology operates on the same basic principles as thick film technology. Rather than using inks or pastes, however, thin film technology uses metals and metal oxides that are evaporated and then deposited on the substrate in the desired pattern to form the integrated circuit s passive components (wires, resistors, and capacitors). See also molecular beam epitaxy. Compare thick film.

thin film transistor n. See TFT.

ThinNet n. See 10Base2.

thin server n. A client/server architecture in which most of an application is run on the client machine, which is called a fat client, with occasional data operations on a remote server. Such a configuration yields good client performance, but complicates administrative tasks, such as software upgrades. See also client/server architecture, fat client, thin client. Compare fat server.

thin space n. An amount of horizontal space in a font, equal to one-quarter the point size of the font. For example, a thin space in a 12-point font is 3 points wide. See also point¹ (definition 1). Compare em space, en space, fixed space.

thin system n. See thin server.

ThinWire n. See 10Base2.

Third Generation n. See 3G.

third-generation computer n. Any of the computers produced from the mid-1960s to the 1970s that were based on integrated circuits rather than on separately wired transistors. See also computer.

third-generation language n. See 3GL.

third normal form n. See normal form (definition 1).

third-party¹ adj. In computer console games, a game made for a specific console by a company other than the console manufacturer.

third party² n. A company that manufactures and sells accessories or peripherals for use with a major manufacturer s computer or peripheral, usually without any involvement from the major manufacturer.

thrashing n. The state of a virtual memory system that is spending almost all its time swapping pages in and out of memory rather than executing applications. See also swap (definition 2), virtual memory.

thread n. 1. In programming, a process that is part of a larger process or program. 2. In a tree data structure, a pointer that identifies the parent node and is used to facilitate traversal of the tree. 3. In electronic mail and Internet newsgroups, a series of messages and replies related to a specific topic.

threaded discussion n. In a newsgroup or other online forum, a series of messages or articles in which replies to an article are nested directly under it, instead of the articles being arranged in chronological or alphabetical order. See also newsgroup, thread (definition 3).

threaded newsreader n. A newsreader that displays posts in newsgroups as threads. Replies to a post appear directly after the original post, rather than in chronological or any other order. See also newsreader, post, thread (definition 3).

threaded tree n. A tree in which the leaf (end) nodes contain pointers to some of the nodes from which they arise. The pointers facilitate searching the tree for information. See also thread (definition 2).

threading n. A technique used by certain interpretive languages, such as many Forth implementations, to speed execution. The references to other support routines in each threaded support routine, such as a predefined word in Forth, are replaced by pointers to those routines. See also Forth, thread (definition 1).

three-dimensional array n. An ordered arrangement of information in which three numbers (integers) are used to locate a particular item. A three-dimensional array treats data as if it were laid out in rows, columns, and layers. See also 3-D array, array, two-dimensional array.

three-dimensional model n. A computer simulation of a physical object in which length, width, and depth are real attributes a model, with x-, y-, and z-axes, that can be rotated for viewing from different angles.

three-finger salute n. Slang term for a warm, or soft, boot, in which the Ctrl, Alt, and Delete keys are pressed simultaneously to restart a computer without first turning off the power. Also called: Vulcan death grip. See also warm boot.

three-nines availability n. The availability of a system 99.9% of the time. Three-nines availability equates to approximately 526 minutes of downtime in a standard 365-day year. See also high availability.

three-point editing n. In digital video editing, a feature that simplifies the process of placing new video within a sequence by assisting in calculating edit points. To make an edit, in and out points must be defined in the video clip to be added and in the sequence into which the clip is to be inserted. The user provides any three of these edit points and the editing software determines the fourth.

three-tier client/server n. A client/server architecture in which software systems are structured into three tiers or layers: the user interface layer, the business logic layer, and the database layer. Layers may have one or more components. For example, there can be one or more user interfaces in the top tier, each user interface may communicate with more than one application in the middle tier at the same time, and the applications in the middle tier may use more than one database at a time. Components in a tier may run on a computer that is separate from the other tiers, communicating with the other components over a network. See also client/server architecture. Compare two-tier client/server.

throbber n. An animated icon that moves while an application is completing a task, such as a browser loading a Web page. Throbbers serve to reassure the user that the application is still working on the task and has not frozen. Web browsers and some other applications come with a throbber icon. In some cases, the user can replace the original throbber with a customized icon of the user s choice.

throttle control n. A device that enables the user of a flight simulator or game to control simulated engine power. The throttle control is used along with a joystick (which controls the simulated ailerons and elevators) and possibly a rudder control.

throughput n. 1. The data transfer rate of a network, measured as the number of bits per second transmitted. 2. A measure of the data processing rate in a computer system.

throughput test n. See bandwidth test.

thumb n. See elevator.

thumbnail n. A miniature version of an image or electronic version of a page that is generally used to allow quick browsing through multiple images or pages. For example, Web pages often contain thumbnails of images (which can be loaded much more quickly by the Web browser than the full-size image). Many of these thumbnails can be clicked on to load the complete version of the image.

thumbwheel n. A wheel embedded in a case so that only a portion of the outside rim is revealed. When rolled with the thumb, the wheel can control an on-screen element such as a pointer or a cursor. Thumbwheels are used with three-dimensional joysticks and trackballs to control the depth aspect of the pointer or cursor. See also joystick, relative pointing device, trackball.

thunk¹ n. Code that enables 16-bit code to call 32-bit code, and vice versa. There are three different types of thunk: a flat thunk relies on a thunk compiler to allow 32-bit code to call a 16-bit DLL and 16-bit code to call a 32-bit DLL; a generic thunk enables a 16-bit application to load and call a 32-bit DLL; and a universal thunk allows 32-bit code to load and call a 16-bit DLL. All thunks are Windows-based, but the type of thunk used depends on the Windows version.

thunk² vb. To call 32-bit code from 16-bit code, or vice versa. Thunking involves, in large part, the translation to and from 16-bit segment offset memory addressing and 32-bit flat, or linear, memory addressing. See also address space, flat address space, segmented address space.

TIA n. Acronym for thanks in advance. On the Internet, a popular sign-off to a request of some sort. Also called: aTdHvAaNnKcSe.

tick n. 1. A regular, rapidly recurring signal emitted by a clocking circuit; also, the interrupt generated by this signal. 2. In some microcomputer systems, notably Macintosh, one sixtieth of a second, the basic time unit used by the internal clock that is accessible by programs.

tiebreaker n. A circuit that arbitrates competing circuits and resolves bottlenecks by giving priority to one circuit at a time.

tie line n. A private line leased from a communications carrier and often used to link two or more points in an organization.

Tier 1 n. An Internet Network Access Point that provides access to and interconnection among major national and international network backbone providers, such as MCI WorldCom, Sprint, BBN, and IBM. See also Network Access Point. Compare Tier 2.

Tier 2 n. A regional Internet Network interchange location where local ISPs exchange data. By using a Tier 2 exchange point, ISPs in the same area can move data between their users without the need to transport that data over long distances. For example, if a user in Singapore connects to a Web site in the same city through a local Tier 2 exchange point, it is not necessary to move the data through a major Network Access Point, or NAP, in Japan or North America. Tier 2 locations generally have much smaller capacities than the national and international Tier 1 NAPs. See also Network Access Point. Compare Tier 1.

.tif or .tiff n. The file extension that identifies bitmap images in Tagged Image File Format (TIFF). See also TIFF.

TIFF or TIF n. Acronym for Tagged Image File Format or Tag Image File Format. A standard file format commonly used for scanning, storage, and interchange of gray-scale graphic images. TIFF may be the only format available for older programs (such as older versions of MacPaint), but most modern programs are able to save images in a variety of other formats, such as GIF or JPEG. See also gray scale. Compare GIF, JPEG.

TIFF JPEG n. Acronym for Tagged Image File Format JPEG. A means of saving photographic images compressed according to the JPEG (Joint Photographic Experts Group) standard. TIFF JPEG saves more information about an image than does the lower-end JFIF (JPEG File Interchange Format), but TIFF JPEG files are limited in portability because of differences in implementation among applications. See also JFIF, JPEG.

TIGA n. Acronym for Texas Instruments Graphics Architecture. A video adapter architecture based on the Texas Instruments 340x0 graphics processor.

tiger team n. A group of users, programmers, or hackers who are charged with finding flaws in networks, applications, or security procedures. Tiger teams may be hired or may be composed of volunteers, and may have a single, short-term goal or may be used for a number of investigative purposes over a longer period of time. The term tiger team was originally used by the military to describe infiltration groups, and was first used in the computer industry to refer to hackers hired to expose flaws in network security.

tightly coupled adj. 1. Refers to two computing processes whose successful completion and individual performance rates are highly interdependent. 2. Of, pertaining to, or characteristic of a relationship of interdependency between computers, as in multiprocessing.

tile vb. 1. In computer-graphics programming, to fill adjacent blocks of pixels on the screen with a design or pattern without allowing any blocks to overlap. 2. To fill the space on a monitor or within a smaller area with multiple copies of the same graphic image. 3. In an environment with multiple windows, to rearrange and resize all open windows so that they appear fully on the screen without any overlap.

time and date n. In computing, the timekeeping and datekeeping functions maintained by the computer s operating system, used most visibly as a means of stamping files with the date and time of creation or last revision.

time and date stamp n. See time stamp.

time bomb n. 1. A feature often built into evaluation or beta versions of software that renders the software unusable after a certain period of time. With some evaluation versions of software containing time bombs, users are given codes or registration numbers after purchasing the software that will deactivate the time bomb. 2. See logic bomb. 3. See Year 2000 problem.

Time Division Multiple Access n. See TDMA.

time-division multiplexing n. A form of multiplexing in which transmission time is broken into segments, each of which carries one element of one signal. Acronym: TDM. See also statistical multiplexer. Compare FDM.

time horizon to failure n. See event horizon.

time out or timeout or time-out n. An event that indicates that a predetermined amount of time has elapsed without some other expected event taking place. The time-out event is used to interrupt the process that had been waiting for the other expected event. For example, a dial-up remote system might allow the user 60 seconds to log in after making a connection. If the user fails to enter a valid login name and password within this time, the computer breaks the connection, thus protecting itself against crackers as well as freeing a phone line that may have gone dead.

timer n. A register (high-speed memory circuit) or a special circuit, chip, or software routine used to measure time intervals. A timer is not the same as the system clock, although its pulses can be derived from the system clock frequency. See also time and date. Compare clock (definition 1), clock/calendar.

time server n. A computer that periodically synchronizes the time on all computers within a network. This ensures that the time used by network services and local functions remains accurate.

time-sharing or timesharing n. 1. The use of a computer system by more than one individual at the same time. Time-sharing runs separate programs concurrently by interleaving portions of processing time allotted to each program (user). See also quantum (definition 2), time slice. 2. A method, used primarily in the 1960s and 1970s, for sharing the capabilities (and cost) of a computer, such as a mainframe. Time-sharing allowed different clients to rent time on a large computer and pay for only the portion of time they used.

time shifting n. A method of dealing with programs with Year 2000 problems that entails modifying the date either in data with which a program works (program encapsulation) or in the input/output logic of the program (data encapsulation). In both cases, the date is moved back in time to process the input, and forward in time to the correct date to produce output. See also encapsulation.

time slice n. A brief period of time during which a particular task is given control of the microprocessor in a time-sharing multitasking environment. See also multitasking, preemptive multitasking. Compare quantum (definition 2).

time-slice multitasking n. See preemptive multitasking.

timestamp n. A certification by a trusted third party specifying that a particular message existed at a specific time and date. In a digital context, trusted third parties generate a trusted timestamp for a particular message by having a timestamping service append a time value to a message and then digitally signing the result. See also digital signature, service.

time stamp n. A time signature that is added by a program or system to files, e-mail messages, or Web pages. A time stamp indicates the time and usually the date when a file or Web page was created or last modified or when an e-mail message was sent or received. Most time stamps are created by programs and are based on the time kept by the system clock of a computer on which the program resides. Commercial time stamp services are available on the Web or by e-mail, and offer proof of posting certificates to corroborate the time and date a message was sent. Also called: date and time stamp, date stamp, time and date stamp.

time-synchronization service n. A program used to ensure that all systems on a network use a common time. Time-synchronization services on the Internet typically update real-time clocks to Universal Time Coordinate (UTC) using Network Time Protocol (NTP). Windows Time Synchronization Service (Win32Time) is a time-synchronization service. See also clock (definition 2), Network Time Protocol, Universal Time Coordinate.

Time to Live n. A header field for a packet sent over the Internet indicating how long the packet should be held. Acronym: TTL. See also header (definition 2), packet (definition 1).

timing attack n. An attack on a cryptographic system that exploits the fact that different cryptographic operations take slightly different amounts of time to process. The attacker exploits these slight time differences by carefully measuring the amount of time required to perform private key operations. Taking these measurements from a vulnerable system can reveal the entire secret key. Cryptographic tokens, network-based cryptosystems, and other applications where attackers can make reasonably accurate timing measurements are potentially at risk from this form of attack.

timing signals n. 1. Any of several types of signals used to coordinate activities within a computer system. 2. A signal used to coordinate data transfer operations.

Tinkerbell program n. A program used to monitor network traffic and alert security administrators when connections are made from a predetermined list of sites and individuals. A Tinkerbell program acts as a low-level security reporting feature.

tiny model n. A memory model in the Intel 80x86 processor family. The tiny model allows a combined total of only 64 kilobytes (KB) for code and for data. See also 8086, memory model.

title bar n. In a graphical user interface, a horizontal space at the top of a window that contains the name of the window. Most title bars also contain boxes or buttons for closing and resizing the window. Clicking on the title bar allows the user to move the entire window.

TLA n. Acronym for three-letter acronym. An ironic term, usually used in jest on the Internet in e-mail, newsgroups, and other online forums, referring to the large number of acronyms in computer terminology, particularly those consisting of three letters.

TLD n. See top-level domain.

TLS n. Acronym for Transport Layer Security. A standard protocol that is used to provide secure Web communications on the Internet or intranets. It enables clients to authenticate servers or, optionally, servers to authenticate clients. It also provides a secure channel by encrypting communications. TLS is the latest and a more secure version of the SSL protocol. See also authentication, communications protocol, SSL.

TMS34010 n. See 34010, 34020.

TN display n. See twisted nematic display.

TOF n. See top-of-file.

toggle¹ n. An electronic device with two states or a program option that can be turned on or off using the same action, such as a mouse click.

toggle² vb. To switch back and forth between two states. For example, the Num Lock key on an IBM-style keyboard toggles the numeric keypad between numbers and cursor movement.

ToggleKeys n. A feature of Windows 9x and Windows NT 4 that sounds high and low beeps when one of the toggle keys (Caps Lock, Num Lock, or Scroll Lock) is turned on or off. See also typematic. Compare BounceKeys, Filter Keys, MouseKeys, ShowSounds, SoundSentry, Sticky Keys.

token n. 1. A unique structured data object or message that circulates continuously among the nodes of a token ring and describes the current state of the network. Before any node can send a message, it must first wait to control the token. See also token bus network, token passing, token ring network. 2. Any nonreducible textual element in data that is being parsed for example, the use in a program of a variable name, a reserved word, or an operator. Storing tokens as short codes shortens program files and speeds execution. See also Basic, parse.

token bus n. The IEEE 802.4 specification for token-passing networks based on a bus or tree topology. Token bus networks were designed primarily for manufacturing but the specification also corresponds to the ARCnet architecture used for LANs.

token bus network n. A LAN (local area network) formed in a bus topology (stations connected to a single, shared data highway) that uses token passing as a means of regulating traffic on the line. On a token bus network, a token governing the right to transmit is passed from one station to another, and each station holds the token for a brief time, during which it alone can transmit information. The token is transferred in order of priority from an upstream station to the next downstream station, which might or might not be the next station on the bus. In essence, the token circles through the network in a logical ring rather than a physical one. Token bus networks are defined in the IEEE 802.4 standards. See also bus network, IEEE 802 standards, token passing. Compare token ring network.

token passing n. A method of controlling network access through the use of a special signal, called a token, that determines which station is allowed to transmit. The token, which is actually a short message or a small packet, is passed from station to station around the network. Only the station with the token can transmit information. See also token bus network, token ring network. Compare collision detection, contention, CSMA/CD.

token ring n. Spelled with lowercase t and r, the IEEE specification 802.5 for token ring networks. See also token ring network.

Token Ring n. See Token Ring network.

token ring network n. A LAN (local area network) formed in a ring (closed loop) topology that uses token passing as a means of regulating traffic on the line. On a token ring network, a token governing the right to transmit is passed from one station to the next in a physical circle. If a station has information to transmit, it seizes the token, marks it as being in use, and inserts the information. The busy token, plus message, is then passed around the circle, copied when it arrives at its destination, and eventually returned to the sender. The sender removes the attached message and then passes the freed token to the next station in line. Token ring networks are defined in the IEEE 802.5 standards. See also IEEE 802 standards, ring network, token passing. Compare token bus network.

Token Ring network n. A token-passing, ring-shaped local area network (LAN) developed by IBM that operates at 4 megabits (4 million bits) per second. With standard telephone wiring, the Token Ring network can connect up to 72 devices; with shielded twisted-pair (STP) wiring, the network supports up to 260 devices. Although it is based on a ring (closed loop) topology, the Token Ring network uses star-shaped clusters of up to eight workstations connected to a wiring concentrator (Multistation Access Unit, or MSAU), which, in turn, is connected to the main ring. The Token Ring network is designed to accommodate microcomputers, minicomputers, and mainframes; it follows the IEEE 802.5 standards for token ring networks. See the illustration. See also ring network, STP, token passing.

Token Ring network. An IBM Token Ring configuration with MSAUs.

tone n. 1. A particular tint of a color. Also called: shade, value. See also brightness, color model. 2. One sound or signal of a particular frequency.

tone compression n. In digital graphics, the compression of the complete color range of an image to the narrower range of the chosen output device. Allowing for tone compression in scanning and graphics editing may improve the quality of the final printed image.

toner n. Powdered pigment that is used in office copiers and in laser, LED, and LCD printers. See also electrophotographic printers.

toner cartridge n. A disposable container that holds toner for a laser printer or other page printer. Some types of toner cartridge contain toner only; however, the most popular printer engines pack all expendables, including toner and the photosensitive drum, in a single cartridge. Toner cartridges are interchangeable among printers that use the same engine.

toolbar n. In an application in a graphical user interface, a row, column, or block of on-screen buttons or icons. When these buttons or icons are clicked on with the mouse, macros or certain functions of the application are activated. For example, word processors often feature toolbars with buttons for changing text to italic, boldface, and other styles. Toolbars often can be customized by the user and usually can be moved around on the screen according to the user s preference. See the illustration. See also graphical user interface. Compare menu bar, palette (definition 1), taskbar, title bar.

Toolbar.

toolbox n. A set of predefined (and usually precompiled) routines a programmer can use in writing a program for a particular machine, environment, or application. Also called: toolkit. See also library (definition 1).

Toolbox n. A set of routines stored mostly in the read-only memory of a Macintosh that provides application programmers with the tools needed to support the graphical interface characteristic of the computer. Also called: User Interface Toolbox.

Tool Command Language/Tool Kit n. See Tcl/Tk.

toolkit n. See toolbox.

ToolTips n. Brief descriptions of the names of buttons and boxes on toolbars and in the toolbox. A ToolTip is displayed when the mouse pointer rests on the button or combo box. See also ScreenTips.

top-down design n. A program design methodology that starts with defining program functionality at the highest level (a series of tasks) and then breaks down each task into lower-level tasks, and so on. See also bottom-up programming, top-down programming. Compare bottom-up design.

top-down programming n. An approach to programming that implements a program in top-down fashion. Typically, this is done by writing a main body with calls to several major routines (implemented as stubs). Each routine is then coded, calling other, lower-level, routines (also done initially as stubs). See also bottom-up design, stub, top-down design. Compare bottom-up programming.

topic drift n. The tendency of an online discussion to move from its original subject to other related or unrelated subjects. For example, someone in a conference devoted to television may ask about a news program; then somebody else may say something about a story on that program about food poisoning, which leads somebody else to start a general discussion on the advantages of organic fruits and vegetables.

topic group n. An online discussion area for participants with a common interest in a particular subject.

top-level domain n. In the domain-name system of Internet addresses or DNS hierarchy, any of the broadest category of names, under which all domain names fit. Top-level domains for sites in the United States include .com, .edu, .gov, .net, and .org. See also DNS (definition 1), major geographic domain.

top-of-file n. 1. The beginning of a file. 2. A symbol used by a program to mark the beginning of a file the first character in the file or, in an indexed (ordered) database, the first indexed record. Acronym: TOF. See also beginning-of-file.

topology n. The configuration or layout of a network formed by the connections between devices on a LAN (local area network) or between two or more LANs. See also bus network, LAN, ring network, star network, token ring network, tree network.

top posting n. In e-mail and newsgroup discussions, placing new material before material quoted from earlier posts rather than after. Because top-posted messages are read out of chronological order, top-posting is considered an undesirable practice.

total bypass n. A communications network that uses satellite transmission to bypass both local and long-distance telephone links.

total cost of ownership n. Specifically, the cost of owning, operating, and maintaining a single PC; more generally, the cost to businesses and organizations of setting up and maintaining complex and far-reaching networked computer systems. Total cost of ownership includes the up-front costs of hardware and software added to later costs of installation, personnel training, technical support, upgrades, and repairs. Industry initiatives designed to lower the total cost of ownership include centralized network management and administration, as well as hardware solutions in the form of network-based computers with or without local storage and expansion capability. Acronym: TCO.

touch pad n. A variety of graphics tablet that uses pressure sensors, rather than the electromagnetics used in more expensive high-resolution tablets, to track the position of a device on its surface. See also absolute pointing device, graphics tablet.

touch screen n. A computer screen designed or modified to recognize the location of a touch on its surface. By touching the screen, the user can make a selection or move a cursor. The simplest type of touch screen is made up of a grid of sensing lines, which determine the location of a touch by matching vertical and horizontal contacts. Another, more accurate type uses an electrically charged surface and sensors around the outer edges of the screen to detect the amount of electrical disruption and pinpoint exactly where contact has been made. A third type has infrared light-emitting diodes (LEDs) and sensors around the outer edges of the screen. These LEDs and sensors create an invisible infrared grid, which the user s finger interrupts, in front of the screen. Compare light pen.

touch-sensitive display n. See touch screen.

touch-sensitive tablet n. See touch pad.

touch tone dialing n. The signaling system used in telephones with touch-tone keypads, in which each digit is associated with two specific frequencies. During dialing, these frequencies for example, 1336 Hz and 697 Hz for the number 2 are transmitted to the telephone company. Also called: DTMF, Dual Tone Multiple Frequency.

tower n. A microcomputer system in which the cabinet for the central processing unit (CPU) is tall, narrow, and deep rather than short, wide, and deep. The motherboard is usually vertical, and the disk drives are often perpendicular to the motherboard. A tower cabinet is at least 24 inches tall. See the illustration. See also cabinet, microcomputer, motherboard. Compare minitower.

Tower.

TP n. See transaction processing.

TPC n. See Transaction Processing Council.

TPC-D n. Acronym for Transaction Processing Council Benchmark D. A benchmark standard that addresses a broad range of decision support applications working with complex data structures. See also Transaction Processing Council.

TPI n. See tracks per inch.

TP monitor n. Short for teleprocessing monitor or transaction processing monitor. A program that controls the transfer of data between terminals (or clients) and a mainframe (or one or more servers) so as to provide a consistent environment for one or more online transaction processing (OLTP) applications. A TP monitor may also control the appearance of the screen displays and check input data for proper format. See also client (definition 3), mainframe computer, OLTP, server (definition 1).

trace vb. To execute a program in such a way that the sequence of statements being executed can be observed. See also debugger, single step.

traceroute n. A utility that shows the route a packet takes through a network to arrive at a remote host. A traceroute also reports the IP addresses of all intermediate hosts or routers and the time required for the packet to reach each of them. See also IP address, packet.

track¹ n. One of numerous circular data storage areas on a floppy disk or a hard drive, comparable to a groove on a record but not spiral. Tracks, composed of sectors, are recorded on a disk by an operating system during a disk format operation. On other storage media, such as tape, a track runs parallel to the edge of the medium. See the illustration.

Track¹. The storage areas on a floppy disk or hard drive.

track² vb. 1. To follow a path. 2. In data management, to follow the flow of information through a manual or an automated system. 3. In data storage and retrieval, to follow and read from a recording channel on a disk or a magnetic tape. 4. In computer graphics, to cause a displayed symbol, such as a pointer, to match on the screen the movements of a mouse or another pointing device.

trackball n. A pointing device that consists of a ball resting on two rollers at right angles to each other, which translate the ball s motion into vertical and horizontal movement on the screen. A trackball also typically has one or more buttons to initiate other actions. A trackball s housing is stationary; its ball is rolled with the hand. See the illustration. Compare mechanical mouse.

Trackball.

tracked change n. A mark that shows where a deletion, insertion, or other editing change has been made in a document.

trackpad n. A pointing device consisting of a small, flat pad that is sensitive to touch. Users move the mouse cursor on screen by touching the trackpad and moving their fingers across the trackpad s surface. Such devices are most commonly installed on laptop computers. See also pointing device.

tracks per inch n. The density with which concentric tracks (data storage rings) are recorded or can be recorded in an inch of radius on a disk. The greater the density (the more tracks per inch), the more information a disk can hold. Acronym: TPI.

tractor feed n. A method of feeding paper through a printer using pins mounted on rotating belts. The pins engage holes near the edges of continuous-form paper and either push or pull the paper through. See also continuous-form paper. Compare pin feed.

trademark n. A word, phrase, symbol, or design (or some combination thereof) used to identify a proprietary product, often accompanied by the symbol ^TM or .

trade show n. A multivendor sales event or exposition that showcases companies products. The computer industry has a number of trade shows every year, including COMDEX.

traditional newsgroup hierarchy n. The seven standard newsgroup categories in Usenet: comp., misc., news., rec., sci., soc., and talk. Newsgroups can be added within the traditional hierarchy only following a formal voting process. See also comp. newsgroups, misc. newsgroups, newsgroup, news. newsgroups, rec. newsgroups, Request for Discussion, sci. newsgroups, soc. newsgroups, talk. newsgroups, Usenet. Compare alt. newsgroups.

traffic n. The load carried by a communications link or channel.

traffic management n. See ITM.

traffic shaping n. A technique for allocating bandwidth and preventing packet loss by enforcing prioritization policies on the transmission of data over a network. Also called: bandwidth shaping. See also bandwidth management, bandwidth reservation, token passing.

trailer n. Information, typically occupying several bytes, at the tail end of a block (section) of transmitted data and often containing a checksum or other error-checking data useful for confirming the accuracy and status of the transmission. See also checksum. Compare header (definition 2).

trailer label n. 1. A small block of information used in tape processing that marks the end of a file or the end of the tape and that can contain other information, such as the number of records in the file or files on the tape. Compare header label. 2. A label used in communications data frames that follows the data and might contain an end-of-message mark, a checksum, and some synchronization bits.

trailing edge n. The latter part of an electronic signal. When a digital signal switches from on to off, the transition is the trailing edge of the signal.

train¹ n. A sequence of items or events, such as a digital pulse train consisting of transmitted binary signals.

train² vb. To teach an end user how to use a software or hardware product.

transaction n. A discrete activity within a computer system, such as an entry of a customer order or an update of an inventory item. Transactions are usually associated with database management, order entry, and other online systems.

transactional e-mail n. A form of Web-based marketing in which goods and services are sold to consumers directly from an e-mail message. Unlike traditional e-mail marketing that requires the e-mail recipient to visit the seller s Web site, transactional e-mail allows an entire sales transaction to be completed from within the marketing e-mail. To take advantage of transactional e-mail buying options, the recipient must view the e-mail message in HTML format.

transaction file n. A file that contains the details of transactions, such as items and prices on invoices. It is used to update a master database file. See also transaction. Compare master file.

transaction log n. See change file.

transaction processing n. A processing method in which transactions are executed immediately after they are received by the system. Acronym: TP. See also transaction. Compare batch processing (definition 3).

Transaction Processing Council n. A group of hardware and software vendors with the goal of publishing benchmark standards. Acronym: TPC.

transaction processing monitor n. See TP monitor.

Transaction Tracking System n. See TTS (definition 2).

Transact-SQL n. A query language. Transact-SQL is sophisticated SQL dialect loaded with additional features beyond what is defined in the ANSI SQL 92 Standard. Also called: T-SQL, TSQL.

transceiver n. Short for transmitter/receiver. A device that can both transmit and receive signals. On LANs (local area networks), a transceiver is the device that connects a computer to the network and that converts signals to and from parallel and serial form.

transceiver cable n. A cable that is used to connect a host adapter within a computer to a LAN (local area network). See also AUI cable, LAN.

transducer n. A device that converts one form of energy into another. Electronic transducers either convert electric energy to another form of energy or convert nonelectric to electric energy.

transfer¹ n. 1. The movement of data from one location to another. 2. The passing of program control from one portion of code to another.

transfer² vb. To move data from one place to another, especially within a single computer. Compare transmit.

transfer rate n. The rate at which a circuit or a communications channel transfers information from source to destination, as over a network or to and from a disk drive. Transfer rate is measured in units of information per unit of time for example, bits per second or characters per second and can be measured either as a raw rate, which is the maximum transfer speed, or as an average rate, which includes gaps between blocks of data as part of the transmission time.

transfer statement n. A statement in a programming language that transfers the flow of execution to another location in the program. See also branch instruction, CALL statement, GOTO statement, jump instruction.

transfer time n. The time elapsed between the start of a data transfer operation and its completion.

transform vb. 1. To change the appearance or format of data without altering its content; that is, to encode information according to predefined rules. 2. In mathematics and computer graphics, to alter the position, size, or nature of an object by moving it to another location (translation), making it larger or smaller (scaling), turning it (rotation), changing its description from one type of coordinate system to another, and so on.

transformer n. A device used to change the voltage of an alternating current signal or to change the impedance of an alternating current circuit.

transient adj. 1. Fleeting, temporary, or unpredictable. 2. Of or pertaining to the region of memory used for programs, such as applications, that are read from disk storage and that reside in memory temporarily until they are replaced by other programs. In this context, transient can also refer to the programs themselves. 3. In electronics, of or pertaining to a short-lived, abnormal, and unpredictable increase in power supply, such as a voltage spike or surge. Transient time is the interval during which a change in current or voltage is building up or decaying.

transient suppressor n. A circuit designed to reduce or eliminate unwanted electrical signals or voltages.

transistor n. Short for transfer resistor. A solid-state circuit component, usually with three leads, in which a voltage or a current controls the flow of another current. The transistor can serve many functions, including those of amplifier, switch, and oscillator, and is a fundamental component of almost all modern electronics. See the illustration. See also base (definition 3), FET, NPN transistor, PNP transistor.

Transistor.

transistor-transistor logic n. A type of bipolar circuit design that utilizes transistors connected to each other either directly or through resistors. Transistor-transistor logic offers high speed and good noise immunity and is used in many digital circuits. A large number of transistor-transistor logic gates can be fabricated on a single integrated circuit. Acronym: TTL.

transitive trust n. The standard type of trust relationship between Windows domains in a domain tree or forest. When a domain joins an existing forest or domain tree, a transitive trust is automatically established. Transitive trusts are always two-way relationships. This series of trusts, between parent and child domains in a domain tree and between root domains of domain trees in a forest, allows all domains in a forest to trust each other for the purposes of authentication. For example, if domain A trusts domain B and domain B trusts domain C, then domain A trusts domain C. See also domain, forest, one-way trust, two-way trust.

translate vb. 1. In programming, to convert a program from one language to another. Translation is performed by special programs such as compilers, assemblers, and interpreters. 2. In computer graphics, to move an image in the space represented on the display, without turning (rotating) the image.

translated file n. A file containing data that has been changed from binary (8-bit) format to ASCII (7-bit) format. BinHex and uuencode both translate binary files into ASCII. Such translation is necessary to transmit data through systems (such as e-mail) that may not preserve the eighth bit of each byte. A translated file must be decoded to its binary form before being used. See also BinHex, uuencode.

translator n. A program that translates one language or data format into another.

transmission channel n. See channel.

Transmission Control Protocol n. See TCP.

Transmission Control Protocol/Internet Protocol n. See TCP/IP.

transmit vb. To send information over a communications line or a circuit. Computer transmissions can take place in the following ways: asynchronous (variable timing) or synchronous (exact timing); serial (essentially, bit by bit) or parallel (byte by byte; a group of bits at once); duplex or full-duplex (simultaneous two-way communication), half-duplex (two-way communication in one direction at a time), or simplex (one-way communication only); and burst (intermittent transmission of blocks of information). Compare transfer².

Transmit Data n. See TXD.

transmitter n. Any circuit or electronic device designed to send electrically encoded data to another location.

transparency n. The quality that defines how much light passes through an object s pixels. If an object is 100 percent transparent, light passes through it completely and renders the object invisible; in other words, you can see through the object.

transparency scanner n. See scanner.

transparent adj. 1. In computer use, of, pertaining to, or characteristic of a device, function, or part of a program that works so smoothly and easily that it is invisible to the user. For example, the ability of one application to use files created by another is transparent if the user encounters no difficulty in opening, reading, or using the second program s files or does not even know the use is occurring. 2. In communications, of, pertaining to, or characteristic of a mode of transmission in which data can include any characters, including device-control characters, without the possibility of misinterpretation by the receiving station. For example, the receiving station will not end a transparent transmission until it receives a character in the data that indicates end of transmission. Thus, there is no danger of the receiving station ending communications prematurely. 3. In computer graphics, of, pertaining to, or characteristic of the lack of color in a particular region of an image so that the background color of the display shows through.

transponder n. A transceiver in a communications satellite that receives a signal from an earth station and retransmits it on a different frequency to one or more other earth stations.

transportable computer n. See portable computer.

transport layer n. The fourth of the seven layers in the International Organization for Standardization s Open Systems Interconnection (OSI) reference model for standardizing computer-to-computer communications. The transport layer is one level above the network layer and is responsible for both quality of service and accurate delivery of information. Among the tasks performed on this layer are error detection and correction. See the illustration. See also ISO/OSI reference model.

Transport layer.

Transport Layer Security n. See TLS.

transpose¹ n. The result of rotating a matrix.

transpose² vb. 1. To reverse, as the order of the letters h and t in hte, in correcting the spelling of the; or reversing two wires in a circuit. 2. In mathematics and spreadsheets, to rotate a matrix (a rectangular array of numbers) about a diagonal axis.

transputer n. Short for transistor computer. A complete computer on a single chip, including RAM and an FPU, designed as a building block for parallel computing systems.

trap¹ n. See interrupt.

trap² vb. 1. To intercept an action or event before it occurs, usually in order to do something else. Trapping is commonly used by debuggers to allow interruption of program execution at a given spot. See also interrupt, interrupt handler. 2. To slightly overlap adjacent colors in preparing material for printing. Page layout and prepress programs trap color to prevent gaps between colors caused by minor variations in registration during printing.

trapdoor n. See back door.

trap handler n. See interrupt handler.

Trash n. An icon on the screen in the Macintosh Finder, resembling a garbage can. To delete a file or eject a diskette, the user drags the icon for the file or diskette to the Trash. However, until the user shuts down the system or chooses the menu option Empty Trash, a file in the Trash is not actually deleted; the user can retrieve it by double-clicking the Trash icon and dragging the file s icon out of the resulting window. Compare Recycle Bin.

traverse vb. In programming, to access in a particular order all of the nodes of a tree or similar data structure.

tree n. A data structure containing zero or more nodes that are linked together in a hierarchical fashion. If there are any nodes, one node is the root; each node except the root is the child of one and only one other node; and each node has zero or more nodes as children. See also child (definition 2), graph, leaf, node (definition 3), parent/child (definition 2), root.

tree network n. A topology for a local area network (LAN) in which one machine is connected to one or more other machines, each of which is connected to one or more others, and so on, so that the structure formed by the network resembles that of a tree. See the illustration. See also bus network, distributed network, ring network, star network, token ring network, topology.

Tree network.

tree search n. A search procedure performed on a tree data structure. At each step of the search, a tree search is able to determine, by the value in a particular node, which branches of the tree to eliminate, without searching those branches themselves. See also branch (definition 1), tree structure.

tree structure n. Any structure that has the essential organizational properties of a tree. See also tree.

tree view n. A hierarchical representation of the folders, files, disk drives, and other resources connected to a computer or network. For example, Windows Explorer uses a tree view to display the resources that are attached to a computer or a network. See also resource.

trellis-coded modulation n. An enhanced form of quadrature amplitude modulation that is used by modems that operate at or above 9,600 bps (bits per second). Trellis-coded modulation encodes information as unique sets of bits associated with changes in both the phase and amplitude of the carrier, as well as using extra signal points for error-checking bits. Acronym: TCM. See also quadrature amplitude modulation.

trendline n. A graphic representation of trends in data series, such as a line sloping upward to represent increased sales over a period of months. Trendlines are used for the study of problems of prediction. Also called: regression analysis.

triage¹ n. The process of prioritizing projects or elements of a project (such as bug fixes) to ensure that available resources are assigned in the most effective, time-efficient, and cost-efficient manner. Traditionally, triage has referred to the prioritization of treatment to the wounded during wartime or medical disaster situations. More recently, the term also refers to anticipating and preventing computer system crashes brought on by the Year 2000 (Y2K) problem. See also Year 2000 Problem.

triage² vb. To identify and prioritize the elements of a project or problem to order them in a way that makes best use of labor, funds, and other resources.

tri-band phone n. A wireless phone designed for international travel. Tri-band phones broadcast on the personal communication service (PCS) frequency used in North America as well as PCS frequencies used in other regions of the world.

trichromatic adj. Of, pertaining to, or characteristic of a system that uses three colors (red, green, and blue in computer graphics) to create all other colors. See also color model.

trigger¹ n. 1. In a database, an action that causes a procedure to be carried out automatically when a user attempts to modify data. A trigger can instruct the database system to take a specific action, depending on the particular change attempted. Incorrect, unwanted, or unauthorized changes can thereby be prevented, helping to maintain the integrity of the database. 2. A function built into a virus or worm that controls the release of a malicious payload or similar event. The trigger may be activated at a predetermined time or date or in response to a user-initiated event, such as opening a specific program or file. In some cases, the trigger may reset itself repeatedly until the virus is neutralized.

trigger² vb. To activate a function or program, such as the release of a virus payload, in response to a specific event, date, or time.

trigonometry n. The branch of mathematics dealing with arcs and angles, expressed in functions (for example, sine and cosine) that show relationships for example, between two sides of a right triangle or between two complementary angles.

trilinear filtering n. A technique used in 3-D computer game rendering and other digital animation applications that produces the illusion of depth of field by making distant objects less distinct and detailed than nearer objects.

tri-mode phone n. A wireless phone that broadcasts on 1900 MHz personal communication service (PCS), 800 MHz digital cellular networks, and 800 MHz analog networks.

triple-pass scanner n. A color scanner that performs one scanning pass on an image for each of the three primary colors of light (red, green, and blue). See also color scanner.

tristimulus values n. In color graphics, the varying amounts of three colors, such as red, blue, and green, that are combined to produce another color. See also color, color model.

Trivial File Transfer Protocol n. A simplified version of File Transfer Protocol (FTP) that provides basic file transfer with no user authentication and is often used to download the initial files needed to begin an installation process. Acronym: TFTP. See also communications protocol.

troff n. Short for typesetting run off. A UNIX text formatter often used to format man pages. See also man pages, RUNOFF. Compare TeX.

Trojan horse n. A destructive program disguised as a game, utility, or application. When run, a Trojan horse does something harmful to the computer system while appearing to do something useful. See also virus, worm.

troll vb. To post a message in a newsgroup or other online conference in the hopes that somebody else will consider the original message so outrageous that it demands a heated reply. A classic example of trolling is an article in favor of torturing cats posted in a pet lovers newsgroup. See also YHBT.

troubleshoot vb. To isolate the source of a problem in a program, computer system, or network and remedy it.

troubleshooter n. A person trained and hired to find and resolve problems or breakdowns in machinery and technical equipment or systems. Troubleshooters often work as short-term consultants or freelancers because many organizations and businesses regard troubleshooting as a short-term effort or possibly an exceptional unplanned part of a project or system. See also troubleshoot.

trouble ticket n. A report of a problem with a particular device or system that is tracked through the workflow process. Originally written on paper, electronic trouble tickets are featured by many workflow and help-desk applications. See also help desk (definition 2), workflow application.

True BASIC n. A version of Basic created in 1983 by John Kemeny and Thomas Kurtz, the creators of the original Basic, to standardize and modernize the language. True BASIC is a compiled, structured version of Basic that does not require line numbers. True BASIC includes advanced control structures that make structured programming possible. See also Basic, structured programming.

true color n. See 24-bit color.

true complement n. See complement.

TrueType n. An outline font technology introduced by Apple Computer, Inc., in 1991 and by Microsoft Corporation in 1992 as a means of including high-grade fonts within the Macintosh and Windows operating systems. TrueType is a WYSIWYG font technology, which means that the printed output of TrueType fonts is identical to what appears on the screen. See also bitmapped font, outline font, PostScript.

TrueType Open version 2 n. See OpenType.

truncate vb. To cut off the beginning or end of a series of characters or numbers; specifically, to eliminate one or more of the least significant (typically rightmost) digits. In truncation, numbers are simply eliminated, unlike rounding, in which the rightmost digit might be incremented to preserve accuracy. Compare round.

trunk n. 1. In communications, a channel connecting two switching stations. A trunk usually carries a large number of calls at the same time. 2. In networking, the cable forming the main communications path on a network. On a bus network, the single cable to which all nodes connect. See also backbone.

trunking n. See link aggregation.

Trusted Computing Base n. See TCB.

trust relationship n. A logical relationship established between domains to allow pass-through authentication, in which a trusting domain honors the logon authentications of a trusted domain. User accounts and global groups defined in a trusted domain can be given rights and permissions in a trusting domain, even though the user accounts or groups don t exist in the trusting domain s directory. See also authentication, domain, group, permission, user account.

truth table n. A table showing the value of a Boolean expression for each of the possible combinations of variable values in the expression. See also AND, Boolean operator, exclusive OR, NOT, OR.

try n. A keyword used in the Java programming language to define a block of statements that may throw a Java language exception. If an exception is thrown, an optional catch block can handle specific exceptions thrown within the try block. Also, an optional finally block will be executed regardless of whether an exception is thrown. See also block, catch, exception, finally.

TSAPI n. Acronym for Telephony Services Application Programming Interface. The set of standards for the interface between a large telephone system and a computer network server, developed by Novell and AT&T and supported by many telephone equipment manufacturers and software developers. Compare TAPI.

TSP n. See Telephony Service Provider.

TSPI n. See Telephony Service Provider Interface.

T-SQL or TSQL n. See Transact-SQL.

TSR n. Acronym for terminate-and-stay-resident. A program that remains loaded in memory even when it is not running, so that it can be quickly invoked for a specific task performed while another program is operating. Typically, these programs are used with operating systems that are not multitasking, such as MS-DOS. See also hot key.

TSV n. Filename extension, short for tab separated values, assigned to text files containing tabular (row and column) data of the type stored in database fields. As the name indicates, individual data entries are separated by tabs. Compare CSV (definition 3).

TTFN n. Acronym for Ta ta for now. An expression sometimes used in Internet discussion groups, such as Internet Relay Chat (IRC), to signal a participant s temporary departure from the group. See also IRC.

TTL n. See Time to Live, transistor-transistor logic.

TTS n. 1. Acronym for Text-to-Speech. The process of converting digital text into speech output. TTS is used extensively in fax, e-mail, and other services for the blind, and for telephone-based informational and financial services. 2. Acronym for Transaction Tracking System. A feature developed to protect databases from corruption caused by incomplete transactions. TTS monitors attempted transactions and in the event of a hardware or software failure, TTS will cancel the update and back out to maintain database integrity.

TTY n. Acronym for teletypewriter. A device for low-speed communications over a telephone line, consisting of a keyboard that sends a character code for each keystroke and a printer that prints characters as their codes are received. The simplest video display interface behaves like a TTY. See also KSR terminal, teletype mode.

tunnel vb. To encapsulate or wrap a packet or a message from one protocol in the packet for another. The wrapped packet is then transmitted over a network via the protocol of the wrapper. This method of packet transmission is used to avoid protocol restrictions. See also communications protocol, packet (definition 2).

tunneling n. A method of transmission over internetworks based on differing protocols. In tunneling, a packet based on one protocol is wrapped, or encapsulated, in a second packet based on whatever differing protocol is needed in order for it to travel over an intermediary network. In effect, the second wrapper insulates the original packet and creates the illusion of a tunnel through which the wrapped packet travels across the intermediary network. In real-life terms, tunneling is comparable to encapsulating a present (the original packet) in a box (the secondary wrapper) for delivery through the postal system.

tunnel server n. A server or router that terminates tunnels and forwards traffic to the hosts on the target network. See also host, router, server, tunnel.

tuple n. In a database table (relation), a set of related values, one for each attribute (column). A tuple is stored as a row in a relational database management system. It is the analog of a record in a nonrelational file. See also relation.

Turing machine n. 1. A theoretical model created by British mathematician Alan Turing in 1936 that is considered the prototype for digital computers. Described in a paper ( On Computable Numbers with an Application to the Entscheidungsproblem ) published in the Proceedings of the London Mathematical Society, the Turing machine was a logical device that could scan one square at a time (either blank or containing a symbol) on a paper tape. Depending on the symbol read from a particular square, the machine would change its status and/or move the tape backward or forward to erase a symbol or to print a new one. See also status. 2. A computer that can successfully mimic human intelligence in the Turing test.

Turing test n. A test of machine intelligence proposed by Alan Turing, British mathematician and developer of the Turing machine. In the Turing test, also known as the Imitation Game, a person uses any series of questions to interrogate two unseen respondents, a human and a computer, to try to determine which is the computer.

turnaround time n. 1. The elapsed time between submission and completion of a job. 2. In communications, the time required to reverse the direction of transmission in half-duplex communication mode. See also half-duplex transmission.

turnkey system n. A finished system, complete with all necessary hardware and documentation and with software installed and ready to be used.

turnpike effect n. The communications equivalent of gridlock; a reference to bottlenecks caused by heavy traffic over a communications system or network.

turtle n. A small on-screen shape, usually a triangle or a turtle shape, that acts as a drawing tool in graphics. A turtle is a friendly, easily manipulated tool designed for children learning to use computers. It takes its name from a mechanical, dome-shaped turtle that was developed for the Logo language and moved about the floor in response to Logo commands, raising and lowering a pen to draw lines.

turtle graphics n. A simple graphics environment, present in Logo and other languages, in which a turtle is manipulated by simple commands. Some versions display the turtle and its track on screen; others use electromechanical turtles that write on paper.

tutorial n. A teaching aid designed to help people learn to use a product or procedure. In computer applications, a tutorial might be presented in either a book or a manual or as an interactive disk-based series of lessons provided with the program package.

Tux n. The mascot of the Linux operating system. Tux is a rotund cartoonish penquin and the Tux image is available for use by any provider of Linux products or services. The name Tux is both short for tuxedo, in reference to a penguin s appearance, and an acronym for Torvalds s UniX, after Linus Torvalds, the creator of the Linux operating system.

TV tuner card n. A PCI card that allows a computer to receive television programming and display it on the computer s monitor. See also PCI card.

TWAIN n. The de facto standard interface between software applications and image-capturing devices such as scanners. Nearly all scanners contain a TWAIN driver, but only TWAIN-compatible software can use the technology. The TWAIN specification was developed by the TWAIN Working Group, a consortium of industry vendors formed in 1992. The name is thought by some to be an acronym for the phrase technology without an interesting name, although the TWAIN Working Group maintains the name is not an acronym. Others attribute the name to the quote Ne er the twain shall meet, because the TWAIN driver and the application receiving the image are separated. See also scanner.

tweak vb. To make final small changes to improve hardware or software performance; to fine-tune a nearly complete product.

tween vb. In a graphics program, to calculate intermediary shapes during the metamorphosis of one shape into another.

twinaxial adj. Having two coaxial cables contained in a single insulated jacket. See also coaxial cable.

twip n. A unit of measure used in typesetting and desktop publishing, equal to one-twentieth of a printer s point, or 1/1440^th of an inch. See also point¹ (definition 1).

twisted nematic display n. A type of passive-matrix liquid crystal display (LCD) in which the glass sheets enclosing nematic liquid crystal material are treated in such a way that the crystal molecules twist 90 degrees between top and bottom in other words, the orientation at the bottom of the crystal is perpendicular to the orientation at the top. When an electrical charge is applied selectively to these crystals, they become temporarily untwisted and block the passage of polarized light. This blockage is what produces the dark pixels on an LCD display. The nematic part of the description refers to microscopic threadlike bodies that characterize the type of liquid crystals used in these displays. Also called: TN display.

twisted-pair cable n. A cable made of two separately insulated strands of wire twisted together. It is used to reduce signal interference introduced by a strong radio source such as a nearby cable. One of the wires in the pair carries the sensitive signal, and the other wire is grounded.

twisted-pair wiring n. Wiring consisting of two insulated strands of copper twisted around one another to form a cable. Twisted-pair wiring comes in two forms, unshielded twisted pair (UTP) and shielded twisted pair (STP), the latter named for an extra protective sheath wrapped around each insulated pair of wires. Twisted-pair wiring can consist of a single pair of wires or, in thicker cables, two, four, or more pairs of wires. Twisted-pair wiring is typical of telephone cabling. Compare coaxial cable, fiberoptic cable.

two-digit date storage n. A limitation in many computer systems and programs that store the year portion of a date as two digits instead of four. This practice in programming dates from the earliest days of computers when space on punch cards and memory in the computer were very limited, and many programmers used a two-digit year in date fields to economize on space or memory requirements.

two-digit shortcut n. The practice of using two digits to indicate the year in a program, particularly those written in programming languages or running on systems that have the capability to work with a four-digit year (hence the term shortcut).

two-dimensional adj. Existing in reference to two measures, such as height and width for example, a two-dimensional model drawn with reference to an x-axis and a y-axis, or a two-dimensional array of numbers placed in rows and columns. See also Cartesian coordinates.

two-dimensional array n. An ordered arrangement of information in which the location of any item is described by two numbers (integers) identifying its position in a particular row and column of a matrix.

two-dimensional model n. A computer simulation of a physical object in which length and width are real attributes but depth is not; a model with x- and y-axes. Compare three-dimensional model.

two-nines availability n. The availability of a system 99% of the time. Two-nines availability equates to approximately 87.6 hours of downtime in a standard 365-day year. See also high availability.

two-out-of-five code n. An error-sensitive code for data transmission that stores each of the ten decimal digits (0 through 9) as a set of five binary digits: either two of the digits are 1s and the other three digits are 0s or two of the digits are 0s and the other three digits are 1s.

two s complement n. A number in the base-2 system (binary system) that is the true complement of another number. A two s complement is usually derived by reversing the digits in a binary number (changing 1s to 0s and 0s to 1s) and adding 1 to the result. When two s complements are used to represent negative numbers, the most significant (leftmost) digit is always 1. See also complement.

two-tier client/server n. A client/business logic layer and the database layer. Fourth-generation languages (4GL) have helped to popularize the two-tier client/server architecture. Compare three-tier client/server.

two-way trust n. A type of trust relationship in which both of the domains in the relationship trust each other. In a two-way trust relationship, each domain has established a one-way trust with the other domain. For example, domain A trusts domain B and domain B trusts domain A. Two-way trusts can be transitive or nontransitive. All two-way trusts between Windows domains in the same domain tree or forest are transitive. See also domain, forest, one-way trust, transitive trust.

TXD n. Short for Transmit (tx) Data. A line used to carry transmitted data from one device to another, as from computer to modem; in RS-232-C connections, pin 2. See also RS-232-C standard. Compare RXD.

.txt n. A file extension that identifies ASCII text files. In most cases, a document with a .txt extension does not include any formatting commands, so it is readable in any text editor or word processing program. See also ASCII.

Tymnet n. A public data network available in over 100 countries, with links to some online services and Internet service providers.

type¹ n. 1. In programming, the nature of a variable for example, integer, real number, text character, or floating-point number. Data types in programs are declared by the programmer and determine the range of values a variable can take as well as the operations that can be performed on it. See also data type. 2. In printing, the characters that make up printed text, the design of a set of characters (typeface), or, more loosely, the complete set of characters in a given size and style (font). See also font, typeface.

type² vb. To enter information by means of the keyboard.

Type I PC Card n. See PC Card.

Type II PC Card n. See PC Card.

Type III PC Card n. See PC Card.

type-ahead buffer n. See keyboard buffer.

type-ahead capability n. The ability of a computer program to gather incoming keystrokes in a temporary memory reservoir (buffer) before displaying them on the screen. This capability ensures that keystrokes are not lost if they are typed faster than the program can display them.

type ball n. A small ball mounted on the print head of a printer or a typewriter (for example, the IBM Selectric) that bears all the characters in the character set on its surface. The ball rotates to align the correct character with the paper and with an inked or carbon ribbon before striking against the paper. See the illustration.

Type ball.

type checking n. The process performed by a compiler or interpreter to make sure that when a variable is used, it is treated as having the same data type as it was declared to have. See also compiler (definition 2), data type, interpreter.

type declaration n. A declaration in a program that specifies the characteristics of a new data type, usually by combining more primitive existing data types.

typeface n. A specific, named design of a set of printed characters, such as Helvetica Bold Oblique, that has a specified obliqueness (degree of slant) and stroke weight (thickness of line). A typeface is not the same as a font, which is a specific size of a specific typeface, such as 12-point Helvetica Bold Oblique. Nor is a typeface the same as a typeface family, which is a group of related typefaces, such as the Helvetica family including Helvetica, Helve tica Bold, Helvetica Oblique, and Helvetica Bold Oblique. See also font.

type font n. See font.

typematic adj. The keyboard feature that repeats a keystroke when a key is held down longer than usual. Also called: auto-key, auto-repeat. See also repeat key, RepeatKeys.

typeover mode n. See overwrite mode.

type size n. The size of printed characters, usually measured in points (a point is approximately ¹/₇₂ inch). See also point¹ (definition 1).

type style n. 1. The obliqueness, or degree of slant, of a typeface. 2. Loosely, the overall design of a typeface or a typeface family. 3. One of the variant forms of a type character, including roman, bold, italic, and bold italic.

typography n. 1. The art of font design and typesetting. See also computer typesetting, font. 2. The conversion of unformatted text into camera-ready type, suitable for printing. See also camera-ready.

typosquatter n. A form of cybersquatter that takes advantage of typographical errors to snare Web surfers. The typosquatter registers variations of popular trademarked domain names that contain the most likely spelling errors (for example: JCPenny). A user who makes a mistake typing in a Web site address will be taken to the typosquatter s site, which typically is loaded with banner and pop-up ads. The typosquatter is paid by the number of users who see the ads. See also cybersquatter.