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. Compare USRT.

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, TCP.

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 information.

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 script.

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 bar code.

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 version.

uplink

n. The transmission link from an earth station to a communications satellite.

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 lowercase.

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.

URI

n. See Uniform Resource Identifier.

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 procedures.

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 secure 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 application.

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