T1
See DS1.
T3
See DS3.
T9
T9 (Text on 9 keys) is a system that uses software to predict what word you intend to enter on a telephone keypad. Multi-tapping is a system for entering characters into a system using a telephone keypad, EG: The letters A, B, and C are associated with the number 2, so to enter B, you would tap the number 2 twice. I find both systems annoying and prefer a full alphanumeric keypad.
TA
Terminal Adaptor. Aka ISDN adaptor. A device which connects a computer to an ISDN line.
Tagged Image File Format
See TIFF.
tape storage
Data storage medium that uses plastic tape embedded with magnetically sensitive material, very much like audio cassette tapes. Tape storage is inexpensive but the data is accessed sequentially instead of randomly like a disk drive. Tape storage is often used for backing up, archiving, and physically transferring large amounts of data.

In order of capacity, the most common formats are QIC (Quarter Inch Cartridge) (40 MB - 10 GB), 4 mm DAT (Digital Audio Tape) (12 GB) , DLT (Digital Linear Tape) (15 GB), 8 mm DAT (20 GB), DC-6000, and Half Inch Cartridge. The most common DAT format is DDS (Digital Data Storage).
Aka process. A program being executed (run) and the bookkeeping information the OS needs to run it. Some OSes, eg UNIX, OS/2, and Windows NT, can multitask, i.e. run multiple tasks at a time. Some OSes can multithread, i.e. break a task down into simultaneously executed parts called threads.
Tar
.tar. Tape ARchive format. Aka tarball. A file archived using the UNIX archiving utility called tar. These files are usually expanded with the following syntax: tar xvf filename.tar. tar archives (turns many files into one) but does not compress (turns one file into a smaller file).
TCO
Total Cost of Ownership. The cost of a system that includes the cost of the hardware and software as well as the salary of staff, consultations, related software, time, etc.
TCP/IP
Transport Control Protocol/Internet Protocol. Developed by the U.S. Dept. of Defense in 1973. Two communications protocols for transferring data such as files and e-mail on a network of computers of nearly any make and model. It is usually faster than regular modem communication.

TCP/IP is the protocol for the Internet, which is a world wide WAN. TCP/IP networks coexist with other network types such as Ethernet.

Typical internet services supported by the TCP/IP suite of protocols are FTP, SMTP, NNTP, telnet, NFS, and HTTP.

TCP implements the transport layer of the OSI Reference Model by making datagrams. IP implements the network and data link layer of the OSI Reference Model by adding an IP address to the header of the TCP datagram.

A TCP/IP connection is connection oriented, i.e. a communication session is established before data is transmitted. TCP utilizes checksum for data integrity. TCP/IP utilizes sockets for endpoints in transmissions.
TDD/TTY
Tone Dialing for the Deaf/Teletype. Compliant with the equipment used by the hard of hearing for typing messages over a phone line.
TDM
Time Division Multiplexing. The core of the PSTN is TDM. See also multiplex.
telco
TELephone COmpany.
television
See TV.
telnet
Terminal Emulation Protocol. A client application that allows a local user to access a remote computer over the phone. The local user's monitor and keyboard virtually become the remote computer's monitor and keyboard,. The specs for telnet, RFC 318 was proposed in 1972.
Terminate and Stay Resident
See TSR.
ternary
A function or operator that has three arguments. See also nullary, unary, and binary.
TeX
A programming language that provides complete control over typographical formatting. Two common macro packages that make it easier to interface with TeX are LaTeX (by Lamport) and plain TeX (by Knuth). MuTeX is a macro package for TeX that is specifically for musical notation. It was written by Steinbach and Schofer.
texel
TEXture ELement. A 2D image is composed of pixels each of which is a single color whereas a 3D image is composed of texels each of which varies in color depending on conditions such as the position and lighting of the 3D object.
text file
.txt. A file containing just ASCII code, i.e. unformatted words, numbers, or characters. A text file is especially not a binary file, which is composed of 0s and 1s, or an executable program, which contains coding geared to execute commands.. A text file may be read as is or it may have data that is coded for interpretation by an application. EG: HTML files (.htm) are text files that are interpreted by browsers. A text file differs from a document file or an executable file. Other common text files include .ini, .dat, .log, and .bat.
Text To Speech
See TTS.
thick coaxial cable
See 10BASE-X.
thin client
See NC.
thin coaxial cable
See 10BASE-X.
thrash
To move vigorously for naught. This refers to a system that either has too few resources, or does not use its resources efficiently. A thrashing system shuffles data around, esp. in and out of virtual memory, instead of executing programs.
(1) A process is said to be executed in threads. The operating system allocates processing time according to threads.  A thread can execute any part of the process code, including parts concurrently executed by other threads.

A fiber is a type of thread that must be manually executed by the application. A job object is a number of processes managed as a unit. See also multithreading.

(2) A particular topic being discussed in a chat room, newsgroup, or exchange of e-mails. A thread is usually associated with the "title" of the messages, but often times the thread wanders. It would be helpful to start a new thread with a new title.
throbber
A graphic in a graphical user interface that animates when the application is undergoing some sort of activity. In addition to some sort of branding, they also provide the user with feedback that they're waiting for something.
thunk
Anything to do with conversions between 16-bit memory addressing and 32-bit memory addressing. Intel's 16-bit microprocessors (8086s to the80286s) and Win 3.X used 16-bit flat address spaces. Intel's 32-bit microprocessors (80386s to the Pentium III)  and Win 95+ use 32 bit segmented memory address spaces. The Mac OS has always used flat addressing.
TIA
tickler file
A task reminder system based roughlyt on the physical tickler file system. The physical tickler file consists of 43 folders: 31 daily folders and 12 monthly folders. These URLS explain the concept: http://www.davidco.com/tips_tools/tip17.html and http://www.overhall.com/tickler_file.htm. Make your own tickler files or buy physical tickler files here: http://www.onlineorganizing.com/Product_PaperConnect_Tickler.htm and http://www.orgcoach.net/products/tickle.html.
TIFF
.tif or .tiff. Tagged Image File Format. A graphic file format often used by DTPs. It is good for high resolution rasterized images, especially scanned images and drawings. It can save in 1 bit (monochrome, usu. black and white), 8 bit   (grayscale or 256 colors), or 24 bit (true color at 16.7 million colors). In 24 b images, TIFF supports transparency by designating an alpha channel to be transparent, i.e. the color will change to the background color.
Time Division Multiplexing
See TDM.
TIMTOWTDI
There Is More Than One Way To Do It. Often pronounced Tim Toady.
tint
To add white to a hue/color. It lightens the value and decreases the saturation, creating a pastel or washed-out look.
title bar
The top of a window where the title of the program or document is displayed.
TLA
Three Letter Acronym.
TLD
Top Level Domain. The rightmost portion of a domain name. See also my section on DNS.
TN3270
See IBM 3270.
token

(1) The smallest lexical component of a programming language. EGs: A keyword, an operator, a variable, a scalar. In C, the six kinds of tokens are keywords, operators, punctuators, identifiers, constants, and string constants. Tokens are separated by positioning, whitespace, or syntax. A compiler typically groups all the characters into tokens and then checks to see if the tokens follow the syntax of the language.

(2) A special series of bits that travels around a token-ring network. Only one token exists on the network and the computer that possesses it is the only one that can transmit.

Token Ring
A scheme for forming a network, second in popularity only to Ethernet. Token Ring is standardized as IEEE 802.5 of the OSI Data Link Layer. A Token Ring is set in a ring topology. See also my section on LANs.
tone
To add black to a hue/color. It darkens the value and decreases the saturation, creating a muddy or darker look.
tool bar
An optional collection of buttons for often used features of a program. The tool bar is usually found underneath the menu bar in a window.
Top Level Domain
See TLD.
topology
The geometric configuration of networks both physically and logically. This includes connecting computers and other devices on networks. There are four basic topologies: Bus, Ring, Star, and Mesh. See also my section on Topologies.
TOS
TP
Transaction Processing. Software processes that ensure that transactions are ACID. In a NCA environment, TPs are typically found on the application server. Examples include IBM's CICS (Customer Information Control System), Microsoft's MTS (Microsoft Transaction Server), NCR's Top End, and BEA's Tuxedo.
trace route
A program that traces how a packet of data hopped between your computer to its originator. If you saw the movie "Sneakers" where their signal was chased around the planet in real time, then you saw an example of a super-duper trace route program. Real life trace route programs include PING programs and tracert for Windows 95.
track
(1) The magnetic "grooves" that form concentric circles on a platter of a hard drive. See also b.

(2) See kern.
transaction
A sequence of operations which must complete in entirety or not at all. If the transaction fails for any reason, the databases involved are rolled back, i.e. returned to their original state. This insures the integrity of a database. Transactions in databases should pass the ACID test. See also ACID.
transaction log
A log of any changes, updates, or deletions by transactions. This aid in rolling back a database to a known state.
transaction monitor
A software system that handles and monitors transactions.
transaction processing
See TP and OLTP.
transceiver
TRANSmitter and reCEIVER. A device that both transmits and receives data. This includes devices like modems and NICs.
transistor
A devices invented in 1947 at Bell Labs that are composed of semiconductors and can amplify a signal or open or close a circuit. Transistors are a key part of electronic devices and digital circuits, including radios, TVs, and computers. The typical chip in a computer has tens of millions of transistors.

Before transistors, digital circuits had to use vacuum tubes. Vacuum tubes were much larger, required more energy, dissipated more heat, and were more prone to failure than transistors
A device which attaches to a flatbed scanner and enables it to scan transparent materials instead of just opaque materials.
Transport Control Protocol/Internet Protocol
See TCP/IP.
Travan
Magnetic tape technology by 3M Corp. It allows higher storage density and is QIC compatible. Travan Level 1 (TR-1) can store 400 MB. TR-2 does 800 MB, TR-3 does 1.6 GB, and TR-4 can store 4 GB. In NS20 format Travan can store 10 GB (20 GB if compressed).
tree
A tree is a conceptual construction which has a finite set of elements called nodes. All the examples below reference the diagram.

A tree has a single node called the root node and all the other nodes are descendants to the root node. The root node is also considered the ancestor of all the other nodes.  EG: G is the root node and all the other nodes are its descendants.

A node can have 0 to n other nodes directly under it called children nodes. EG: D is a child of G and B is a child of D, but B is not a child of G (you could call it a grandchild).

A node that has children is called a parent node. EG: G, D, I, B, and F are all parent nodes.

Nodes that share the same parent node are called sibling nodes. EG: B and F are sibling nodes.

If each node in a tree is limited to 0-1 children, then it is a called a linear tree. If each node in a tree is limited to 0-2 children, then it is a binary tree.

A parent node that is not the root node and all its descendants are called a sub-tree. EG: Node I, H, and J form a sub-tree.

A node that has no children is called a leaf node. EG: C and E are both leaf nodes.

treemap
'Treemap is a space-constrained visualization of hierarchical structures. It is very effective in showing attributes of leaf nodes using size and color coding. Treemap enables users to compare nodes and sub-trees even at varying depth in the tree, and help them spot patterns and exceptions. Treemap was first designed by Ben Shneiderman during the 1990s.' [ref]
trigger
A type of stored procedure that executes automatically when certain data is tapped into. Triggers can be used to maintain consistency between related tables and enforce referential integrity.
Trojan
Malicious software disguised as something harmless.
TrueType
Scalable, cross platform, outline fonts developed in 1991. Each letter is described via a mathematical formula outlining the letter and can therefore be shown in any size, unlike bitmapped fonts.
truncate
To shorten by cutting off and usually the fractional portion of a number, eg 3.14159265 becomes 3.
truth table
A table used in boolean algebra or boolean logic to display the results of logical operators in tabular format. The results are either true or false, where true is sometimes expressed as "Yes" or "1", and false is sometimes expressed as "No" or "0". In computers frequently zero inputs --such as "no" and empty string ('')-- are treated as "false", while non-zero input --such as "yes", 17, and "dog"-- are treated as "true". Ambiguous input --undefined and null-- may be processed differently depending upon the system. See also Binary Numbers.
TSR
Terminate and Stay Resident. A program that stays resident in RAM, by loading up very early at start up, often times even before the operating system is loaded.
TTFN
Ta-Ta For Now.
TTS
.tts. Text To Speech. The translation of text to a computer audio impersonation of a human voice. Voice may be impersonated by computer voice synthesis or by diaphone concatenation. Computer speech synthesis generates sounds like the necessary phonemes. Diaphone concatenation is hours of recorded beginning and ending phoneme units, eg "hello" is  silence-h h-eh eh-l l-o o-silence.
TTYL
Talk To You Later.
tunneling
Encapsulating packets of one protocol within another. This is used for transporting data in a LAN protocol across a network of a different protocol. Typically:
• A passenger protocol (eg PPP or SLIP) contains the data.
• An encapsulating protocol (eg L2F) creates, maintains, and destroys the tunnel which encapsulates the passenger protocol.
• A carrier protocol (eg IP) carries the encapsulating protocol.
tuple
In mathematics, a tuple is a finite sequence of objects. Tuples come in lengths: single, pairs, triplets, quadruples, quinttuples, sextuples, setptuples, octuples, etc. EG: A tuple in Cartesian 2D system using only positive integers up to 3, would yield pairs, (x,y) specifying the interesections. The total set of possible tuples would be {(1,1),(1,2),(1,3),(2,1),(2,2),(2,3),(3,1),(3,2),(3,3)}. Tuples can have very context specific meaning in computers. See also my article on Multi-Dimensional cubes.
Turing Machine
A theoretical machine developed by Alan Turing in 1936. It demonstrates that a simple machine can solve any problem. Computers and programs are nothing but soupped up Turing Machines. The essential elements of a Turing Machine are:
1. A finite set of symbols (including the blank symbol), which the machine can discriminate and recognize.
2. A tape (which is as long as needed to hold the input, the computation, and the output); the tape is divided into cells, with one of the symbols printed in each cell.
3. A set of four tape operations: read(), write(aSymbol), moveLeft(), and moveRight(). read() returns the symbol printed in the currently scanned cell while write(aSymbol) prints aSymbol on the currently scanned cell; moveLeft() moves left one cell to an adjacent cell while moveRight() moves right one cell to an adjacent cell.
4. A finite set of states, one of which is a "halt" state (which signifies that the machine has finished its computation);
5. A set of situation-reaction rules, where a situation is the current state and the current scanned symbol; the reaction is a transition to the next state (which may be the same as the current state) and a tape operation or operations (writing, optionally, a new symbol on the current cell and moving left or right to one of the two adjacent cell). One situation is singled out as the machine's initial situation.
Turing Test
A subjective test developed by Alan Turing in 1950 to answer the question, "Can machines think?". If a computer acts, reacts and interacts like a sentient being, then it is sentient. Here is the basic test: a human interrogator is isolated and given the task of distinguishing between a human and a computer based on their replies to questions that the interrogator poses. After a series of tests are performed, the interrogator attempts to determine which subject is human, and which is an artificial intelligence. The computer's success at thinking can be quantified by its probability of being misidentified as the human subject.
TV

TeleVision. A mechanical version of the TV was invented by German Paul Gottlieb Nipkow in 1884. In the 1920s the MTV was further developed by John Logie Baird for Britain and Charles Francis Jenkins for the US. German Karl Braun invented the CRT (Cathode Ray Tube), i.e. the electronic TV in 1897. The CRT was further developed by Russian Dr. Vladimir Kosma Zworykin in 1929. Philo T. Farnsworth was the first to transmit TV signals in 1927.  See also my article on Video.

TWAIN
Technology (or Toolkit) Without An Interesting Name. The de facto driver for scanners.
twip
A unit of measurement created by Microsoft.
     1 in =     6 pc =   72 pt = 1440 twip
1/6 in =     1 pc =   12 pt =  240 twip
1/72 in =  1/12 pc =    1 pt =   20 twip
1/1440 in = 1/240 pc = 1/20 pt =    1 twip
txt
See ASCII Text.
type
A variable (or its corresponding literals) are said to be of a particular variety or type. There are so called "primitive" types like boolean, number, string, undefined, and null. There are so called "non-primitive types like arrays and objects.
Type 1, Type 3
See PS.
typeface
An alphabet and the accompanying miscellaneous characters with a particular design.
A compound document file that has information about types and objects exposed to other applications by a server. A type library is often shipped as a .dll, a .exe, or as a stand alone binary file.