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Glossary Of Computer Terms
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E F G H I J K L M N O
P Q R S T U V W X Y Z
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UART: n. Acronym for universal asynchronous receiver-transmitter. A module,
usually composed of a single integrated circuit, that contains both the receiving and transmitting circuits required
for asynchronous serial communication. A UART is the most common type of circuit used in personal computer modems.
UDP: n. Acronym for User Datagram Protocol. The connectionless protocol within
TCP/IP that corresponds to the transport layer in the ISO/OSI model. UDP converts data messages generated by an
application into packets to be sent via IP but does not verify that messages have been delivered correctly. Therefore,
UDP is more efficient than TCP, so it is used for various purposes, including SNMP; the reliability depends on
the application that generates the message. See also ISO/OSI model, packet, protocol, SNMP, TCP/IP. Compare IP,
UDT: n. Acronym for uniform data transfer. The service used in the OLE extensions
to Microsoft Windows that allows two applications to exchange data without either program knowing the internal
structure of the other.
Ultra DMA/33: n. A recently developed data transfer protocol based on direct
memory access. Ultra DMA/33 improves ATA/IDE performance, doubles burst transfer rates to 33 megabytes per second,
and increases data transfer integrity. See also ATA, direct memory access, IDE (definition 1).
UltraSCSI: n. An extension of the SCSI-2 standard that doubles the transfer
speed of Fast-SCSI to allow a transfer rate of 20 megabytes per second (Mbps) on an 8-bit connection and 40 megabytes
per second (Mbps) on a 16-bit connection. See also SCSI, SCSI-2.
UMA: n. Acronym for upper memory area. The portion of DOS memory between the
first 640K and 1 megabyte. Compare high memory area.
UMB: n. Acronym for upper memory block. A block of memory in the UMA (upper
memory area) that can be used for device drivers or TSRs. A UMB is allocated and managed by special memory manager
programs such as EMM386.EXE. See also device driver, TSR, UMA.
UNC: n. See Uniform Naming Convention.
undelete1: n. The act of restoring deleted information. An undelete is comparable
to (and usually included as part of) an "undo" command; it is more restricted, however, in that undo
reverses any previous act, but undelete reverses only a deletion. Undelete generally refers only to excised text
or deleted files. See also undo.
undelete2: vb. 1. To restore deleted information, usually the last item deleted.
2. In file storage, to restore a file's storage information so that a deleted file becomes available for access
again. Also called unerase. See also file recovery.
undeliverable: adj. Not able to be delivered to an intended recipient. If an
e-mail message is undeliverable, it is returned to the sender with information added by the mail server explaining
the problem; for example, the e-mail address may be incorrect, or the recipient's mailbox may be full.
underline: vb. To format a selection of text so that the text is printed with
a line slightly below it.
Undernet: n. An international network of Internet Relay Chat (IRC) servers,
created in 1992 as an alternative to the larger and more chaotic main IRC network. For information about connecting
to Undernet, see http://www.undernet.org. See also IRC.
underscore: n. An underline character often used to emphasize a letter or a
word; on nongraphics displays, generally used to indicate italic characters.
undo: vb. To reverse the last action--for example, to undo a deletion, thus
restoring deleted text to a document. Many application programs enable the user both to undo and to redo an action.
See also undelete.
undock: vb. 1. To detach a laptop or other portable computer from a docking
station. See also docking station, laptop. 2. To move a toolbar from the edge of a window so that the toolbar becomes
its own free-floating window. See also toolbar.
Unicode: n. A 16-bit character encoding standard developed by the Unicode Consortium
between 1988 and 1991. By using two bytes to represent each character, Unicode enables almost all of the written
languages of the world to be represented using a single character set. (By contrast, 8-bit ASCII is not capable
of representing all of the combinations of letters and diacritical marks that are used just with the Roman alphabet.)
Approximately 39,000 of the 65,536 possible Unicode character codes have been assigned to date, 21,000 of them
being used for Chinese ideographs. The remaining combinations are open for expansion. Compare ASCII.
Uniform Data Transfer: n. See UDT.
Uniform Naming Convention: n. The system of naming files among computers on a network so that a file on a given
computer will have the same pathname when accessed from any of the other computers on the network. For example,
if the directory c:\path1\path2\...pathn on computer servern is shared under the name pathdirs, a user on another
computer would open \\servern\pathdirs\filename.ext to access the file c:\path1\path2\...pathn\filename.ext on
servern. See also URL, virtual path.
Uniform Resource Citation: n. A description of an object on the World Wide
Web, consisting of pairs of attributes and their values, such as the Uniform Resource Identifiers (URIs) of associated
resources, author names, publisher names, dates, and prices. Acronym: URC.
Uniform Resource Locator: n. See URL.
Uniform Resource Name: n. A scheme for uniquely identifying resources that
may be available on the Internet by name, without regard to where they are located. The specifications for the
format of Uniform Resource Names are still under development by the Internet Engineering Task Force (IETF). They
include all Uniform Resource Identifiers (URIs) having the schemes urn:, fpi:, and path:; that is, those that are
not Uniform Resource Locators (URLs). See also IETF, Uniform Resource Identifier, URL. Acronym: URN.
uninstall: vb. To remove software completely from a system, including the elimination
of files and components residing in system locations such as the Registry in Windows 95 or Windows NT. Some applications
have built-in uninstall utilities, and in other cases a separate uninstall program can be used. Also called deinstall.
UNIVAC I: n. Short for Universal Automatic Calculator. The first commercially
available electronic computer, designed by J. Presper Eckert and John Mauchly, also the inventors of ENIAC (generally
considered the first fully electronic computer). UNIVAC I was the first computer to handle both numeric and textual
Universal Time Coordinate: n. For all practical purposes, the same as Greenwich
Mean Time, which is used for the synchronization of computers on the Internet. Also called coordinated universal
time format. Acronym: UTC.
UNIX: n. A multiuser, multitasking operating system originally developed by
Ken Thompson and Dennis Ritchie at AT&T Bell Laboratories in 1969 for use on minicomputers. UNIX is considered
a powerful operating system that, because it is written in the C language, is more portable--that is, less machine-specific--than
other operating systems. UNIX is available in several related forms, including AIX (a version of UNIX adapted by
IBM to run on RISC-based workstations), A/UX (a graphical version for the Apple Macintosh), and Mach (a rewritten
but essentially UNIX-compatible operating system for the NeXT computer). See also BSD UNIX, GNU, Linux.
UNIX shell account: n. A shell account providing command-line access to a UNIX
system. See also shell account.
UNIX shell scripts: n. Sequences of UNIX commands stored as files that can
be run as programs. In MS-DOS, batch (.bat) files provide similar capabilities. See also batch file, shell1, shell
unknown host: n. A response to a request for a connection to a server that
indicates that the network is unable to find the specified address. See also server (defintion 1).
unknown recipients: n. A response to an e-mail message that indicates that
the mail server is unable to identify one or more of the destination addresses.
unload: vb. 1. To remove a storage medium, such as a tape or disk, from its
drive. 2. To remove software from system memory. See also memory.
unmoderated: adj. Of, pertaining to, or characteristic of a newsgroup or mailing
list in which all articles or messages received by the server are automatically available or distributed to all
subscribers. Compare moderated.
unmount: vb. To remove a disk or tape from active use. Compare mount.
unread: adj. 1. Of, pertaining to, or being an article in a newsgroup that
a user has not yet received. Newsreader client programs distinguish between "read" and "unread"
articles for each user and download only unread articles from the server. 2. Of, pertaining to, or being an e-mail
message that a user has received but has not yet opened in an e-mail program.
unrecoverable error: n. A fatal error--one that a program is unable to recover from without the use of external
recovery techniques. Compare recoverable error.
unshielded cable: n. Cable that is not surrounded with a metal shield. If the
wires in an unshielded cable are not at least twisted around each other in pairs, the signals they carry have no
protection from interference by external electromagnetic fields. Consequently, unshielded cable should be used
only over very short distances. Compare coaxial cable, ribbon cable, twisted-pair cable, UTP.
unsubscribe: vb. 1. In a newsreader client program, to remove a newsgroup from
the list of newsgroups to which one subscribes. See also newsgroup. 2. To remove a recipient from a mailing list.
See also mailing list.
unzip: vb. To uncompress an archive file that has been compressed by a program
such as compress, gzip, or PKZIP.
up: adj. Functioning and available for use; used in describing computers, printers,
communications lines on networks, and other such hardware.
UPC: n. Acronym for Universal Product Code. A system of numbering commercial
products using bar codes. A UPC consists of 12 digits: a number system character, a five-digit number assigned
to the manufacturer, a five-digit product code assigned by the manufacturer, and a modulo 10 check digit. See also
update1: n. A new release of an existing software product. A software update
usually adds relatively minor new features to a product or corrects errors (bugs) found after the program was released.
Updates are generally indicated by small changes in software version numbers, such as 4.0b from 4.0. See also version
number. Compare release1.
update2: vb. To change a system or a data file to make it more current.
upgrade1: n. The new or enhanced version of a product.
upgrade2: vb. To change to a newer, usually more powerful or sophisticated
uplink: n. The transmission link from an earth station to a communications
upload1: n. 1. In communications, the process of transferring a copy of a file
from a local computer to a remote computer by means of a modem or network. 2. The copy of the file that is being
or has been transferred.
upload2: vb. To transfer a copy of a file from a local computer to a remote
computer. Compare download.
uppercase: adj. Of, pertaining to, or characterized by capital letters. Compare
UPS: n. Acronym for uninterruptible power supply. A device, connected between
a computer (or other electronic equipment) and a power source (usually an outlet receptacle), that ensures that
electrical flow to the computer is not interrupted because of a blackout and, in most cases, protects the computer
against potentially damaging events, such as power surges and brownouts. All UPS units are equipped with a battery
and a loss-of-power sensor; if the sensor detects a loss of power, it switches over to the battery so that the
user has time to save his or her work and shut off the computer. See also blackout, brownout.
URC: n. See Uniform Resource Citation.
URL: n. Acronym for Uniform Resource Locator. An address for a resource on
the Internet. URLs are used by Web browsers to locate Internet resources. A URL specifies the protocol to be used
in accessing the resource (such as http: for a World Wide Web page or ftp: for an FTP site), the name of the server
on which the resource resides (such as //www.whitehouse.gov), and, optionally, the path to a resource (such as
an HTML document or a file on that server). See also FTP1 (definition 1), HTML, HTTP, path (definition 1), server
(definition 2), virtual path (definition 1), Web browser.
URN: n. See Uniform Resource Name.
usable: adj. Of, pertaining to, or characteristic of the ease and adaptability
with which a product can be applied to the performance of the work for which it is designed. A high degree of usability
implies ease of learning, flexibility, freedom from bugs, and good design that does not involve unnecessarily complicated
USB: n. Acronym for universal serial bus. A serial bus with a bandwidth of
1.5 megabits per second (Mbps) for connecting peripherals to a microcomputer. USB can connect up to 127 peripherals,
such as external CD-ROM drives, printers, modems, mice, and keyboards, to the system through a single, general-purpose
port. This is accomplished by daisy chaining peripherals together. USB supports hot plugging and multiple data
streams. Developed by Intel, USB competes with DEC's ACCESS.bus for lower-speed applications. See also bus, daisy
chain, hot plugging, input/output port, peripheral. Compare ACCESS.bus.
U.S. Department of Defense: n. The military branch of the United Staes government.
The Department of Defense developed ARPANET, the origin of today's Internet and MILNET, through its Advanced Research
Projects Agency. See also ARPANET, Internet, MILNET.
Usenet or USENET or UseNet: n. A worldwide network of UNIX systems that has a decentralized administration
and is used as a bulletin board system by special-interest discussion groups. Usenet, which is considered part
of the Internet (although Usenet predates it), is composed of thousands of newsgroups, each devoted to a particular
topic. Users can post messages and read messages from others in these newsgroups in a manner similar to users on
dial-in BBSs. Usenet was originally implemented using UUCP (UNIX-to-UNIX Copy) software and telephone connections;
that method remains important, although more modern methods, such as NNTP and network connections, are more commonly
used. See also BBS (definition 1), newsgroup, newsreader, NNTP, UUCP.
Usenet User List: n. A list maintained by the Massachusetts Institute of Technology
that contains the name and e-mail address of everyone who has posted to the Usenet. See also Usenet.
user account: n. On a security-enhanced or multiuser computer system,
an established means for an individual to gain access to the system and its resources. Usually created by the system's
administrator, a user account consists of information about the user, such as password,
rights, and permissions. See also group1, logon, user profile.
user-friendly: adj. Easy to learn and easy to use.
user group: n. A group of people drawn together by interest in the same computer
system or software. User groups, some of which are large and influential organizations, provide support for newcomers
and a forum where members can exchange ideas and information.
user name: n. The name by which a person is known and addressed on a communications
network. See also alias (definition 2).
username: n. The name by which a user is identified to a computer system or
network. During the logon process, the user must enter the username and the correct password. If the system or
network is connected to the Internet, the username generally corresponds to the leftmost part of the user's e-mail
address. See also e-mail address, logon.
user profile: n. A computer-based record maintained about an authorized user
of a multiuser computer system. A user profile is needed for security and other reasons; it can contain such information
as the person's access restrictions, mailbox location, type of terminal, and so on. See also user account.
USRT: n. Acronym for universal synchronous receiver-transmitter. A module,
usually composed of a single integrated circuit, that contains both the receiving and transmitting circuits required
for synchronous serial communication. Compare UART.
utility: n. A program designed to perform a particular function; the term usually
refers to software that solves narrowly focused problems or those related to computer system management. See also
utility program: n. A program designed to perform maintenance work on the system
or on system components (e.g., a storage backup program, disk and file recovery program, or resource editor).
UTP: n. Acronym for unshielded twisted pair. A cable containing one or more
twisted pairs of wires without additional shielding. UTP is more flexible and takes up less space than shielded
twisted-pair (STP) cable but has less bandwidth. See also twisted-pair cable. Compare STP.
UUCP: n. Acronym for UNIX-to-UNIX Copy. A set of software programs that facilitate
transmission of information between UNIX systems using serial data connections, primarily the public switched telephone
network. See also uupc.
uudecode1: n. A UNIX program that converts a uuencoded file back into its original
binary format. This program (along with uuencode) allows binary data, such as images or executable code, to be
disseminated through e-mail or newsgroups. Compare uuencode1.
uudecode2: vb. To transform a uuencoded file back into its binary original
using the uudecode program. Compare uuencode2.
uuencode1: n. A UNIX program that converts a binary file, in which all 8 bits
of every byte are significant, into printable 7-bit ASCII characters without loss of information. This program
(along with uudecode) allows binary data, such as images or executable code, to be disseminated through e-mail
or newsgroups. A file thus encoded is one-third again as long as the original. Compare uudecode1.
uuencode2: vb. To transform a binary file into printable 7-bit ASCII text using
the uuencode program. Compare uudecode2.
uupc: n. The version of UUCP for IBM PCs and PC-compatibles running DOS, Windows,
or OS/2. This version is a collection of programs for copying files to, logging in to, and running programs on
remote networked computers. See also UUCP.
The contributors of these definitions is far too numerous to mention, however
if you see something that you feel shouldn't be here let us know.