U

U INTERFACE

A 2-wire ISDN circuit-essentially today's standard one pair telephone company local loop made of twisted-wire. The U interface is the most common ISDN interface. See ISDN.

U/L

Universal/Local

UA

IC part number prefix indicating Fairchild Semiconductor. (Actually a "micro" symbol, not a U)

UA

Unnumbered Acknowledgement OR User Agent

UCL

University College London Protocol

UDP

User Defined Primitives (Logic simulation acronym)

UDP

See User Datagram Protocol.

UHF

FCC defined as 300 to 3000MHz (TV 14 through 83).

ULP

Upper Layer Protocols

ULTIMEDIA

IBM's product that supports both Ultimotion and Indeo™ video technology.

ULTIMOTION

IBM's video compression algorithm. Although IBM supports Indeo™ video technology in OS/2 and Windows systems, IBM feels several OS/2 vertical applications are adequately served by the Ultimotion algorithm. Ultimotion does not offer software scalable playback or single step compression.

UMB

See Upper Memory Block.

UNA

See Universal Network Architecture.

UNCONNECTED SOCKET

A socket which has not been bound to a permanent destination. See also Socket.

UNDERFLOW BIT

A bit that is set to indicate that the result of an operation is less than theminimum value that can be contained in a register.

UNIVERSAL NETWORK ARCHITECTURE

(UNA) Novell's proprietary network architecture, based on XNS and very similar to TCP/IP. UNA includes protocols and packet formats that enable the system of data communications between workstations and servers on a NetWare network. The protocols and packet formats include Internetwork Packet Exchange (IPX), Sequenced Packet Exchange (SPX), NetWare Core Protocol (NCP), Router Information Protocol (RIP), and Service Advertising Protocol (SAP).

UNIVERSAL PRODUCT CODE

(UPC) The standard bar code for retail food packages in the United States.

UNIVERSAL RESOURCE LOCATOR

(URL) Internet addresses or URLs describe World Wide Web sites. This lengthy series or words and punctuation marks can be typed in directly.

UNIVERSAL SERVICE ORDER CODE

Old Bell system term for particular service or equipment offered under tariff.

UNIVERSAL SYNCHRONOUS / ASYNCHRONOUS RECEIVER/TRANS-MITTER

(USART) A UART with the added capability for synchronous data communication.

UNIX

A miltitasking, multiuser computer operating system developed by AT&T. Several versions exist, e.g. the Berkeley version.

UNIX TO UNIX COPY PROGRAM

(UUCP) A protocol used for communication between consenting UNIX systems.

UNIXWARE

A UNIX System V Release 4.2 operating system developed and produced by Univel, which includes support for NetWare networking. UnixWare Application Server is an operating system that incorporates NetWare server and routing functions and support for IPX communications. UnixWare Personal Edition is a workstation UNIX operating system that incorporates NetWare workstation connectivity with the capability to run UNIX, DOS, and Windows applications at the desktop under either the X-Windows or Motif graphical user interfaces.

UNKNOWN VIRUS

A virus not yet identified, but can sometimes be detected by observing changes in files that could result from infection.

UNMA

Unified Network Management Architecture

UNRESTRICTED SERVICE LINE

An ISDN trunk capable of operating at 64Kbps. Unrestricted Service Line is standard in Europe, some are available in the United States.

UNSHIELDED TWISTED-PAIR

(UTP) By far, the most popular type of LAN cabling. It is easy to work with, flexible, low cost, has small diameter, is lightweight, and is simple to connect and terminate. It supports wide-ranging applications including voice, ISDN, Ethernet, Token Ring, Fast Ethernet, FDDI, and even Asynchronous Transfer Mode (ATM). UTP commonly consists of four pairs of 24 AWG solid or stranded copper wire surrounded by a thin insulating jacket. The most important standards reference for those interested in LAN cabling is the Electronic Industries Association/Telecommunications Industry Association (EIA/TIA) standard 58A. See UTP Levels. See Twisted Pair.

UNUSED DISK SECTOR VIRUS

Viruses frequently make use of unused disk sectors to conceal their operation. For example, partition table and boot sector infectors frequently make use of the fact that most of the first cylinder of a hard disk is unused. Viruses can copy the original partition table or boot sector to one of these unused sectors without destroying any data. These viruses are therefore able to survive undetected on the disk longer. See Dir-2 virus.

UPC

See Universal Product Code.

UPGRADE

Improved version of a program with the old bugs taken out and new ones put in.

UPPER MEMORY AREA

The part of physical memory that starts at 640K and ends at 1024K (hexadecimal addresses A000 through FFFF). Also called the adapter segment, because that portion of memory is often used by hardware adapters such as display adapters. The unused parts of the upper memory area. For an 80386 or higher computer, information can be mapped (or copied) from another type of memory to upper memory blocks, freeing more conventional memory. See Upper Memory Block.

UPPER MEMORY BLOCK

(UMB) Memory in the range 640-1024Kb, just above the DOS 640Kb limit of conventional memory.

UPPER MEMORY BLOCK

(UMB) Also known as High RAM and Upper-Memory. Normally expanded memory only REQUIRES a 64K page frame. But, many LIM 4.0 compatible expanded memory boards (such as Intel memory boards) automatically try to provide as large a page frame as possible, up to 128K (if there are no ROM's within this range also using some of this space), within the C000-DFFF range. These additional pages of expanded memory in the page frame can be used to create Upper Memory Blocks, which are blocks of memory that can be used to load device drivers and TSR's into them in order to free up more conventional memory for your applications. Basically, every extra page of expanded memory outside of the first 64K of the pageframe can be turned into a UMB. There are memory managers available that create these UMB's. UMB providers in 8088, 8086, and 80286 based systems: 1. QRAM 2. MOVEM These memory managers require that the available Upper Memory Blocks first be made mappable by the combination of a LIM 4.0 Expanded Memory Manager and a memory card such as Intel's EMM.SYS devicedriver and an Intel Above Board. The Above Board Plus and Above Board Plus 8 can map extra 16K blocks of memory within the C000-DFFF address range beyond the first 64K (which has to remain intact so that applications that use expanded memory will still be able to use it). UMB providers in i386 and i486 based systems: 1. EMM386.SYS provided with DOS 5.0 2. QEMM 3. 386MAX These memory managers do not require LIM 4.0 expanded memory board because the i386 and i486 microprocessors have "mapping" capabilities built into them. 386 memory managers simply use extended memory to emulate expanded and also UMB's. See Upper Memory Area.

URL

See Universal Resource Locator.

USART

See Universal synchronous/asynchronous receiver/transmitter

USENET

A loosely-organized network of millions of computers worldwide. These computers are linked in a number of ways, including modems and TCP/IP based local area networks. The best known service provided by Usenet is Usenet News.

USER ACCOUNT

A record in the User Account database that contains security specifications for a particular user. It is organized by user ID and includes information such as passphrase and privilege. It is managed by a LAN Distance security administrator.

USER ACCOUNT DATABASE

A directory of LAN Distance user information. It is used to to perform user identification and authentication for establishing LAN Distance connections and restricting access to certain tasks.

USER CONTEXT

A user session created by an operating system in response to a logon request, and typically characterized by privilege sets that strictly define the user's authority to access system resources and information. Contexts restrict unauthorized access to facilities and data and protect the system itself from user and applications interference, accidental or otherwise. Contexts are a feature of most multiuser operating systems, usually integrated with the security system.

USER DATAGRAM PROTOCOL

An unverified (usually called unreliable) connectionless transport protocol.

USER ID

User identification; a unique name that identifies a user.

USER PROFILE

A DOS batch file containing commands that are automatically executed when you log on. These commands can be used to set environment variables and to run programs automatically when you log on.

USER TYPE

A specific type of user that is granted a fixed set of privileges. Each different type of user is granted a different set of privileges. See User, Administrator, and Security Administrator.

USERS

Compact list of users on the system (UNIX command)

USERS

Active Users Protocol

USOC

See Universal Service Order Code.

UTP

See Unshielded Twisted Pair

UTP LEVEL 1 VOICE

Level 1 cables are manufactured to meet minimum telecommunications.cable requirements. Typical uses include analog and digital voice.plus low speed data (20 kbps). Intended for basic communications and power-limited circuit cable. There are no performance criteria for this category. Functional equivalent of UL Level 1. Not rated for any application-Nondatagrade.

UTP LEVEL 2 ISDN AND LOW SPEED DATA

These cables support the IBM Type 3 Media requirement. Most uses are defined through the IBM Cabling System guidelines. This.specification defines electrical requirements through 1 MHz. Low-performance UTP. Typical applications include voice and low-speed data not specified in EIA/TIA 568A for data use Functional equivalent of UL Level or IBM Type 3.

UTP LEVEL 3 LAN & MEDIUM SPEED DATA

These products support the ANSI/EIA/TIA-568 Commercial Building.Telecommincations Wiring Standard specification horizontal cable.(also known as Category 3). This standard defines cable performance through 16 MHz and thus supports high speed LAN applications. IBM Type 3 Voice/PBX Alarm wiring - Nondatagrade. Category 3 applies to UTP cables and associated connecting hardware with transmission characteristics up to 16 MHz. Functional equivalent of UL Level 3 10BASE-T 4 Mbps Token Ring ARCnet 100BASE-VG - Nondatagrade

UTP LEVEL 4 EXTENDED DISTANCE LAN

Level 4 cables are specifically designed for LAN applications. Most.UTP LANs require a higher degree of performance than the standard.telecommunications design offers. Level 4 cables require performance testing through 20 MHz and provide outstanding crosstalk isolation.and attenuations. They are ideal for extended distance 10BaseT.(<=135 meters) and 16 Mbps Token Ring. Applies to UTP cables and associated connecting hardware with characteristics up to 20 MHz. Functional equivalent of UL Level 4. 16 Mbps Token Ring low transmission 10BASE-T - Datagrade

UTP LEVEL 5 HIGH SPEED LAN 100 OHM & 150 OHM - DGM

This level requires the ultimate design for 100 ohm UTP cable. These cables are intended to be used up to and including 100 Mbps CDDI.applications. The 150 ohm shielded twisted pair (STP) data grade media is the cornerstone of the IBM Cabling System. In addition to the many IBM applications, this cable is now supported by a consortium of 5 system vendors for 100 Mbps twisted pair transmission until the ANSI X3T9.5 standard is completed. Applies to UTP, ScTP, or STP cables and associated connecting hardware with transmission characteristics up to 100 MHz. Functional equivalent of UL Level 5. ATM over copper TP-PMD CDDI 100BASE-X - Datagrade

UUCP

See UNIX to UNIX Copy Program.

UUCP-PATH

UUCP Path Service. See UUCP.

UUENCODE/DECODE

A utility that allows binary-file mail transmission by encrypting binary files as text mail messages. The receiver must UUDecode UUEncoded files.