Barrons Publishing Dictionary of Computer and Internet Terms 10th

thread

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thread

1.a series of messages in a discussion forum, each responding to the previous one. See NEWSGROUP.

2.a task or process in a computer program that uses MULTITASKING. For example, a word processor might have one thread to accept keystrokes from the keyboard, and another thread, running concurrently, to keep the screen updated. The Java programming language is designed to facilitate the creation of programs with more than one thread.

threaded discussion an online discussion where users can post comments. Users can reply to a previous post, which may have been a reply to an earlier post. This keeps the replies organized in a hierarchical pattern so readers can easily follow the thread of one discussion.

threaded interpretive language a programming language in which programs are stored almost exclusively as lists of addresses of subroutines.

See FORTH.

threadjacking the act of deliberately switching the topic of a forum thread; intentional TOPIC DRIFT. An example would be a thread on cooking being threadjacked by someone posting Michelle Obama’s shortbread cookie recipe with a long ramble on politics, switching the thread from its original purpose (recipes) to a new discussion (politics).

three-dimensional graphics the process of representing three-dimensional images on a two-dimensional computer screen. This ability is especially important in CAD and in games. For example, imagine that you are designing a house, and your computer program lets you simulate walking through the different rooms. The computer needs to keep track of three-dimensional coordinates of the points of the house, and it needs to know which points are connected with lines, which planes should be filled in (as in a wall) or left open (as in a door). To allow the user to view the image from different points, the computer needs to be able to translate or rotate the points as directed. Particularly in a game setting, the computer needs to redraw the entire screen very quickly to maintain the illusion of rapid motion.

A simple kind of image is a wireframe view, which shows only the basic structure of an object, not the details of surfaces. This type of image is particularly helpful when designing pieces that need to fit together.

Three-dimensional images can be transmitted to other computers using the VRML language. See VRML.

three-dimensional mouse a handheld joystick-like device that allows movement in three dimensions by rotating, pulling, or pushing along at least three axes.

three-dimensional printer a device analogous to a computer printer that makes three-dimensional objects instead of marks on paper. Threedimensional printers typically work by spraying thin layers of plastic, one

477

thumb

after another, to form the desired shape. The result is a ready-to-use plastic object, such as a prototype of a machine part. See RAPID PROTOTYPING.

FIGURE 262. Three-dimensional graphics

three-finger salute (slang) Ctrl-Alt-Del.

three-tier architecture a database system with a user interface running on a microcomputer, a database engine running on a mainframe computer or other powerful enterprise-wide computer, and a layer of MIDDLEWARE that connects these two tiers. See UML.

thumb the box on an elevator bar (scroll bar). The position of the thumb gives a graphical representation of the window’s current position in the document or list. If you are near the top of the document, the thumb is near the top of the bar; if you are near the bottom of the document, the thumb is near the bottom of the bar. The thumb can be dragged with the mouse to scroll rapidly around the page.

FIGURE 263. Thumbs

thumb drive

478

thumb drive see USB FLASH DRIVE.

thumbnail (from the artists’ term thumbnail sketch) a small image of a graphics file displayed in order to help you identify it.

Thumbs.db a system file in which Windows stores thumbnail representations of graphics. Windows may create a Thumbs.db file in any directory (folder), and the file can be deleted without harm, since it will be re-gen- erated if needed.

THX on-line abbreviation for “thanks.”

TIA online abbreviation for “thanks in advance.”

tick marks short lines that cross another line to mark the points increments of measurement in a graph.

FIGURE 264. Tick marks

ticket a record of a problem that is being diagnosed or repaired. Originally a slip of paper, a ticket is now usually a record maintained online, and “open a ticket” means “make a request for technical assistance.”

tickler a program that examines the computer system’s date and alerts the user about scheduled events.

TIFF (Tag Image File Format) a format for storing bitmapped images on disk, developed by Aldus, Microsoft, and several other companies. TIFF files can store very large images with millions of colors, using several kinds of data compression. Compare GIF; JPEG. See also BITMAP.

tight type set so closely that the letters almost touch. See LETTERSPACING for illustration. See also KERNING; TRACKING.

tilde the character ~. Under UNIX and in many web addresses, the tilde indicates the home directory of a particular user; for example, ~smith is the home directory of the user named smith.

tile

1. to cause windows to divide the screen into sections without overlapping one another (Figure 265). Contrast CASCADE; OVERLAID WINDOWS.

479	timesharing

2.to print a large page (larger than your printer can handle) by having the page broken up into a series of regular-sized sheets, which can then be fastened together.

3.to create a pattern with a simple design by repeating it over and over. Many draw and paint programs have a library of tile designs; you can also design your own.

tiled windows windows that divide the screen into sections without overlapping one another. Contrast CASCADE; OVERLAID WINDOWS.

FIGURE 265. Tiled windows

timeout failure of an operation because it has exceeded the allowable time. This usually means that something else went wrong first, such as loss of a network connection.

Times Roman a highly legible typeface designed by Stanley Morison in 1931 for The Times of London. Times Roman and its many varieties (Times New Roman, Dutch 801, and others) reproduce well at low resolutions, and this probably led to its current popularity as a laser printer font. This book is set in Adobe Times Roman. See TYPEFACE.

timesharing a technique developed in the 1960s for running more than one program on the same computer at the same time, so that, for example, the computer can serve many users at different terminals simultaneously.

Timesharing is based on the idea that a computer spends most of its time waiting for things to happen. Almost all input-output devices (printers, disks, etc.) operate much more slowly than the CPU itself; the extreme case is a terminal or console where the computer may spend minutes or hours waiting for someone to type something. In a timesharing system, more than one program is loaded into memory at once, and when the computer is unable to proceed with one program, it jumps to another.

In practice, the computer does not stay on one program more than a fraction of a second even if there is nothing to wait for: to do so would prevent other, possibly shorter, programs from being executed. Also, programs that are not executed are frequently “rolled out” of memory (i.e., copied to disk) to make memory space available to programs that are actually running.

tint

480

Modern operating systems such as UNIX and Windows use timesharing to run multiple programs concurrently. See MULTITASKING.

tint a shade of a color; usually expressed as a percentage of a solid color. See Figure 266.

FIGURE 266. Tints of black

title (on a web page) descriptive text that defines the title of a web page and displays it in the browser’s status bar. See WEB PAGE TITLE.

title bar the horizontal bar at the top of a window that contains the application program’s icon and name at the left, the name of the open file (if appropriate), and to the right, the trio of window control buttons (MINIMIZE, RESTORE [or full-screen], and CLOSE). See Figure 267. In Windows, clicking on the application program’s icon will pop up a menu to control the window.

FIGURE 267. Title bar and set of possible buttons

TLA three-letter acronym; three-letter abbreviation. A significant obstacle to progress in the computer industry is the fact that there are only 17,576 TLAs, of which some, such as UGH, do not make good trademarks.

TLD (top-level domain) (TLD) the last part of a web or e-mail address, such as .com, .uk, or the like.

Top-level domains are administered by registrars ultimately licensed by ICANN (see ICANN). Some TLDs are administered by only one registrar, and some, such as .com, are shared by many.

There are three basic types of TLDs. First, the original set, dating from the early days of the Internet:

.com commercial entities

.edu university-level educational institutions

.gov the U.S. government

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toggle

.int international organizations

(such as the ITU and United Nations)

.mil U.S. military sites

.net network service providers

.org non-profit organizations

These are used mostly in the United States, although, except for .mil, they can be assigned anywhere. Other early TLDs, such as .uucp and

.bitnet, stood for connections to other networks, and are no longer used. At the end of the 1990s, several registrars began using .com, .net, and

.org indiscriminately for all types of sites. In 2000, ICANN authorized an additional set of international TLDs, as follows:

.aero	aeronautical industry sites
.biz	business sites of all types
.coop	cooperatives (customer-owned businesses)
.info	sites of all types
.museum	museums
.name	individual persons
.pro	licensed professionals (lawyers, etc.)

Meanwhile, an official set of country code TLDs (ccTLDs) was adopted and maintained. For a complete listing of the ccTLDs, see the tables on pages 552 to 554. Note that the code for the United States, .us, is seldom used.

Most of these ccTLDs are used only in the country to which they belong, but some, such as .tv and .ws, have been resold for use elsewhere—a source of income for small countries, and confusion for everyone else. See also CCTLD; GTLD; ICANN.

In 2008 ICANN announced it would start considering a significant expansion of the number of TLDs by considering proposed new names from other organizations.

tn see TELNET.

tn3270 see TELNET.

TNC terminal-node controller. See PACKET RADIO.

TNX abbreviation for thanks, sometimes written TNXE6 or TNX1E6 to signify “thanks a million” (see EXPONENTIAL NOTATION).

to back; send to back comparable commands that send the selected object to the bottom layer. See also ARRANGE; BACK ONE; BRING FORWARD; DRAW PROGRAM; FORWARD ONE; SEND BACKWARD; SEND TO FRONT; TO FRONT.

to front; bring to front comparable commands that send the selected object to the top layer. See also ARRANGE; BACK ONE; BRING FORWARD; DRAW PROGRAM; FORWARD ONE; SEND BACKWARD; SEND TO BACK; TO BACK.

toggle to switch something back and forth from one state to another. For instance, in some editors, the Ins key “toggles” insert mode; that is, it turns insert mode on if it is off or off if it is on.

token

482

token

1.the special message that is passed around a TOKEN-RING NETWORK to enable the computers to take turns transmitting.

2.one of the items in a set, whether or not distinguishable from the others. For example, the list {a,a,b,c,c} contains five tokens but only three types. Contrast TYPE (definition 3).

3.a basic meaningful unit of a language. For example, the one-line BASIC program

10 PRINT ”The square root of 2 is ”;SQR(2)

consists of ten tokens:

(Some people do not count the spaces as tokens.) Breaking the input into tokens is the first step in processing any computer language.

token-identical absolutely identical, not just similar; the same instance of the same object. For example, the capital of the United States is tokenidentical with the city of Washington; they are the same thing, described two different ways. Contrast TYPE-IDENTICAL.

token-ring network a type of network in which the computers are connected together in a ring. A special message, called the token, is passed from one machine to another around the ring, and each machine can transmit only while it is holding the token. IBM marketed a token-ring network for the PC family of computers. See LOCAL-AREA NETWORK.

tokenize to break a character string into the smallest units that are significant in a language (see TOKEN, definition 3).

toner the black powder that is used by laser printers and photocopy machines to create the image on paper. It consists of tiny particles of easily melted plastic. If you spill toner where it isn’t wanted, make sure it doesn’t become hot before cleaning up; if the tiny particles melt, they will stick permanently to any surface.

toner cartridge replaceable assembly in a laser printer that contains the toner (a powdery ink) that will be used to make marks on the paper. Most toner cartridges also contain other parts that are likely to wear out (e.g., the electrophotographic drum), and replacing the cartridge replaces quite a bit of the inner workings of the laser printer. (This contributes to the cost of the toner cartridge.) Some types of toner cartridges are recyclable and refillable; however, the quality of refilled cartridges is not always equal to that of new ones.

tool a specialized version of the mouse cursor that gives the cursor new abilities and properties. For example, in a paint program, the brush tool

483

torrent

will have a special shape, size, and color—any pixels touched by the “brush” will change to the brush color.

toolbox a collection of icons that represent frequently used commands. A toolbox may be displayed across the top or side of the screen or you may be able to relocate it by dragging it with the mouse. The more complicated paint programs sometimes have several toolboxes, with similar tools grouped together. See DOCK.

FIGURE 268. Toolbox

top-down programming a technique of programming by defining the overall outlines of the program first and then filling in the details.

The top-down approach is usually the best way to write complicated programs. Detailed decisions are postponed until the requirements of the large program are known; this is better than making the detailed decisions early and then forcing the major program strategy to conform to them. Each part of the program (called a module) can be written and tested independently. See also STUB.

topic drift the tendency of the topic of an online discussion to shift while the title of the messages remains the same, because everyone is replying to an existing message and therefore automatically keeping the same title. After a while, a THREAD titled “Windows Vista setup” may actually be discussing chili recipes. Topic drift can be particularly amusing when reading a newsgroup frequented by individuals with wide-ranging interests. See LURK; NEWSGROUP; THREAD.

topology the mathematical study of how points are connected together. If an object is stretched or bent, then its geometric shape changes but its topology remains unchanged.

The topology of a computer network is the pattern of connections between the machines in the network. Figure 269 illustrates some common topologies: a ring network, a star network, and a bus network. See

LOCAL-AREA NETWORK.

torrent a file ready to be downloaded by the BitTorrent method. See BITTORRENT.

touchpad

484

FIGURE 269. Topologies of computer networks

touchpad a substitute for a MOUSE on a laptop or notebook computer (Figure 270). The user uses a finger to make strokes on a rectangular touch sensor. Just as with a mouse, the direction and length of the strokes is significant, but not their absolute position.

FIGURE 270. Touchpad (on a laptop computer).

touchscreen a computer screen that is sensitive to touch, so that the user can point to things on it by touching the screen itself, without using a mouse.

trace

1.to execute a program step by step, observing the results of each step.

2.(in a draw program) to create a path or outline around the contours of a bitmapped shape. It is necessary to trace bitmaps to convert them into VECTOR GRAPHICS. Tracing can be done by a separate utility program or

from within the drawing program.

track

1.one of the concentric circles in which data is recorded on a disk (Figure 271), or one of the parallel strips in which data is recorded on tape.

2.a music selection on a CD-ROM.

3.a video selection on a DVD.

4.a portion of a MIDI file that specifies the performance details of a single instrument.

485	trade secret

FIGURE 271. Track

trackball a computer pointing device similar in function to a mouse. Instead of rolling the mouse around the desktop, the user rotates the ball on the trackball in the direction desired. The trackball unit itself does not move, which is an advantage if there is not enough desktop space to conveniently operate a mouse.

FIGURE 272. Trackball

tracking letterspacing (spacing between letters in words). See LETTERSPACING for an illustration.

tracking cookie a COOKIE that sends reports listing what web pages you visit back to the source of the cookie. Unlike other cookies that may improve your web browsing by storing your preferences for viewing certain web pages, the tracking cookies are solely for the benefit of advertisers and are often installed on your machine without your knowledge.

tractor feed a mechanism that uses toothed gears to pull the paper forward in a dot-matrix computer printer. The teeth fit into the feed holes in the side of the paper.

trade secret a piece of information (usually about the design or manufacturing of a product) that is kept secret because it gives the maker an advantage over competitors. A famous trade secret is the formula for Coca-Cola.

The security of a trade secret depends on successfully keeping outsiders from knowing it. Patents, by contrast, are openly disclosed to the public, with a prohibition against unauthorized use.

The internal workings of most software packages are trade secrets, but it is somewhat unclear whether software licenses can actually