10BASE2 A specification for thin coaxial cable often used with the IEEE 802.3 LAN standard.
10BASE5 A specification for thick backbone cable often used with the IEEE 802.3 LAN standard.
10BASET A specification for twisted-pair cable often used with the IEEE 802.3 and 802.5 LAN standards.
100BASET Also known as Fast Ethernet. An extension of the IEEE 802.3 LAN standard that boosts the speed of an Ethernet network from 10 Mbps to 100 Mbps. The three layers of 100BASET include 100BASE-TX, supporting Category 5 UTP and STP cabling; 100BASE-T4, supporting Category 3, 4 and 5 UTP cabling; and 100BASE-FX, supporting two-strand fiber optic cable.
20/20 A VAX-based spreadsheet package developed by Access Technology and often used in conjunction with Digital Equipment's ALL-IN-1. See also ALL-IN-1.
360 See System/360.
370 See System/370.
390 See System/390.
802.2 See IEEE 802.2.
802.3 See IEEE 802.3.
802.4 See IEEE 802.4.
802.5 See IEEE 802.5.
2780/3780 IBM Remote Job Entry (RJE) stations. This symmetrical protocol is often used in the context of the IBM bisynchronous contention protocol that directs the flow of activity between these RJE stations and the mainframe. It is also frequently used to implement RJE from one type of computer to another. 2780/3780 stations are non-SNA devices. See also RJE.
3080 An IBM System/370 mainframe.
3090 An IBM System/370 mainframe.
3151 An IBM ASCII workstation (for multivendor compatibility).
3164 An IBM ASCII workstation (for multivendor compatibility).
3174 IBM control unit for the 3270 workstation family. An SNA Physical Unit (PU) Type 2. See also 3270, 3274 and 3276.
3178 A 3270 workstation (LU 2). See 3270.
3179 A 3270 color workstation (LU 2). See 3270.
3180 A 5250 workstation (LU 7). See 5250.
3196 A 5250 workstation (LU 7). See 5250.
3197 A 5250 color workstation (LU 7). See 5250.
3262 A 3270 printer (LU 3). See 3270.
3268 A 3270 printer (LU 3). See 3270.
3270 A family of IBM workstations and printers generally used with IBM mainframes (9370, 4300, and 3090). Members of the 3270 family include the 3178 display station, 3179 color display station, 3278 display station, 3279 color display station, 3287 printer, and others. These units interface with the 3174, 3274, or 3276 control unit. In SNA terms, they are defined as Logical Unit (LU) Types 2 (3270 workstations) and Type 3 (3270 printers).
3274 An IBM control unit for the 3270 workstation family. The 3274 connects one or more 3270 devices with a host computer via a communications control node (3705, 3720, 3725 or 3745) or Integrated Communications Adapter. In SNA terms, the IBM control unit is defined as a Physical Unit (PU) Type 2. See also 3270, 3174, and 3276.
3276 IBM control unit for the 3270 workstation family. The 3276 is a 3274 with a built-in terminal. Like the 3274, it is a Physical Unit (PU) Type 2 but also includes a Logical Unit (LU) Type 2. See also 3270, 3174 and 3274.
3277 A 3270 workstation (LU 2). See 3270.
3278 A 3270 workstation (LU 2). See 3270.
3279 A 3270 color workstation (LU 2). See 3270.
3287 A 3270 printer (LU 3). See 3270.
3289 A 3270 printer (LU 3). See 3270.
3705 An IBM communication control node. Interfaces the mainframe to 3274 control units. In SNA, this is a Physical Unit (PU) Type 4. See also 3270, 3720, 3725, and 3745.
3720 IBM communication control node. In SNA, a Physical Unit (PU) Type 4 device. See also 3270, 3705, 3725, and 3745.
3725 A later model of the IBM 3720 communications control node and an SNA Physical Unit (PU) Type 4 device. See also 3270, 3705, 3720, and 3745.
3745 An IBM communications control node. In SNA, a Physical Unit (PU) Type 4 device. See also 3270, 3705, 3720, and 3725.
3770 An IBM RJE workstation that supports a console, printers, card readers, and card punches. The 3770 is similar to the 2780 and 3780 RJE workstations in function but interacts with the host (mainframe) in a slightly different manner. The 3770 is a Logical Unit (LU) Type 1 SNA device. See also RJE.
3780 See 2780/3780.
3812 A 5250 printer (LU 4). See 5250.
4210 A 5250 printer (LU 4). See 5250.
4214 A 5250 printer (LU 4). See 5250.
4224 A 5250 printer (LU 4). See 5250.
4225 A 5250 printer (LU 4). See 5250.
4234 A 5250 printer (LU 4). See 5250.
4245 A 5250 printer (LU 4). See 5250.
4250 A 3270 printer (LU 3). See 3270.
4300 An IBM System/370 mainframe.
5210 A 3270 printer (LU 3). See 3270.
5219 A 5250 printer (LU 4). See 5250.
5224 A 5250 printer (LU 4). See 5250.
5225 A 5250 printer (LU 4). See 5250.
5250 A family of IBM workstations and printers used with IBM's mid-range computer line (AS/400, System/36, and System/38). Members of this family include the 5251 display station, 5291 display station, 3197 color display station, 5256 printer, and others. These units interface with the 5294 or 5394 control unit. The 5250 family is classified as an SNA Logical Unit (LU) Type 7 device for workstations and a Type 4 device for printers.
5251 A 5250 workstation (LU 7). See 5250.
5256 A 5250 printer (LU 4). See 5250.
5262 A 5250 printer (LU 4). See 5250.
5291 A 5250 workstation (LU 7). See 5250.
5292 A 5250 color workstation (LU 7). See 5250.
5294 An IBM control unit for the 5250 workstation family. The 5294 interfaces with a mid-range host. In SNA terms, the 5294 is an SNA Physical Unit (PU) Type 2. See also 5250 and 5394.
5360 An IBM System/36 mid-range system.
5380 An IBM System/38 mid-range system.
5394 Like the 5294, a control unit for the 5250 workstation family (and a PU 2 device). See also 5250 and 5294.
9402 The system unit designation for the low end of the AS/400 mid-range system line. The 9402 system unit includes the D04 and D06 models.
9404 The system unit designation for the middle of the AS/400 mid-range system line. The 9404 system unit includes the D10 through D25 models.
9406 The system unit designation for the high end of the AS/400 mid-range system line. The 9406 system unit includes the D35 through D80 models.
9370 An IBM System/370 mainframe.
Accumaster Integrator An AT&T network management product that collects and reports network information generated by AT&T's Network Management Protocol (NMP).
ACF Advanced Communications Functions. An IBM prefix attached to products that support SNA functions. For example, ACF/VTAM indicates that this version of VTAM supports SNA devices.
ACK Acknowledgment. A control character transmitted by a receiver as an affirmative response to the sender.
ACU Automatic call unit. A device used with a standard modem to dial the telephone number for the originating equipment. Dedicated ACU devices were popular (and necessary) before the advent of Hayes and Hayes-compatible modems. ACUs work with asynchronous or synchronous modems.
ADCC Asynchronous Data Communication Controller. An HP asynchronous controller card for the CISC models of the HP 3000 computer line. The ADCC is used to interface terminals with the computer via either the RS-232C or RS-422 standards. See also ATP and DTC.
ADCCP Advanced Data Communications Control Protocol. The ANSI implementation of a bit-oriented, symmetrical protocol based on IBM SDLC. Because of the ANSI endorsement, support for ADCCP is often specified in connectivity situations involving the U.S. government.
address A set of bits (or bytes) that uniquely identifies a device on a multidropped (or multipoint) data communications line or in a network.
ADSL Asymmetric Digital Subscriber Line. A transport technology capable of significantly increasing the capacity of existing phone lines.
Aegis A proprietary operating system for Apollo's Domain engineering workstations.
AIX Advanced Interactive Executive. IBM's primary (but not only) implementation of UNIX. Versions of AIX are available for IBM engineering workstations, PS/2s and for the System/370 mainframe systems. See also IX.
ALLBASE/SQL A HP product for the HP 3000 to implement networkwide databases.
ALL-IN-1 DEC's electronic mail and office automation product for the VAX system.
analog transmission Transmissions in which the native data processing digital signals are converted into waveforms for transmission. This transmission is used when sending information over voice-grade phone lines. See also digital transmission.
ANI Automatic number identification. A service implemented by ISDN that enables the receiver of a phone call to see the phone number of the caller on a special display. See also ISDN.
ANSI American National Standards Institute. ANSI is a nonprofit, nongovernmental body supported by more than 1,000 trade organizations, professional societies and companies. ANSI is the American representation at ISO.
API Application program interface. Originally an IBM term, API has now taken on a much broader usage. API refers to an interface available to an application for communicating with other applications. See also APPC, IPC, and RPC.
Apollo An engineering workstation manufacturing company that was acquired by HP in 1989. Apollo's products, its Domain line, used both conventional (Motorola MC68000-series processors) and parallel RISC technology (which Apollo termed PRISM).
APPC Advanced Program-to-Program Communications. An IBM term used to refer to an interface that enables two programs running on separate systems to communicate with one another. In most cases, APPC refers to the LU 6.2 interface. See also API, IPC, and RPC.
AppleTalk Apple's CSMA/CD-based LAN technology.
Application Layer The seventh (top) layer of the OSI Reference Model. The Application Layer defines services available to the application and to the user. This layer includes utility functions such as file transfer and virtual terminal services. See also OSI Reference Model.
APPN Advanced Peer-to-Peer Networking. An IBM term that refers to the capability of two intelligent microcomputer systems in a network to communicate directly without involving any higher-level SNA devices. In most cases, APPN refers to the capability of two PU 2.1 devices to communicate with one another.
Arcnet A LAN implementation developed by Datapoint that uses a token-passing discipline operating over a 2.5 Mbps physical network. Arcnet became popular in implementing early PC networks because it offered a reasonable level of performance at a reasonable price. Arcnet can be implemented in many topologies, but it is usually implemented as a star.
ARPA Advanced Research Projects Agency. Now called DARPA. See DARPA.
AS/400 Introduced in 1988 as the flagship of IBM's mid-range product line. The AS/400 (Application System/400) was modeled after both the System/36 and System/38--the two systems the AS/400 was targeted to replace.
AS/400 Office IBM's electronic mail and office automation product for the AS/400.
ASCII American Standard Code for Information Interchange. An ANSI-defined code that defines the bit composition of characters and symbols. ASCII defines 128 different symbols using 7 binary bits (the eighth bit is reserved for parity). DEC, HP, and Sun all use the ASCII encoding system, although larger IBM platforms use EBCDIC--a similar but incompatible code. See also EBCDIC.
ASP Attached Support Processor. An IBM Job Entry Subsystem for the OS/SVS operating system. See also JES.
Asynchronous A data transmission method in which each character (eight bits) transmitted is bounded by a start bit and one or more stop bits. Under asynchronous communications, no timing or clocking information is exchanged between parties. See also Synchronous.
Asynchronous Transfer Mode (ATM) A high-speed protocol that offers every client on the network the capability to send data at speeds up to 155 Mbps.
ATP Advanced Terminal Processor. A HP asynchronous controller card for HP 3000 CISC computers. The ATP interfaces terminals with the computer using either RS-232C or RS-422 standards. The ATP is similar to the ADCC, but can perform more functions locally. See also ADCC and DTC.
AUI Attachment unit interface. The interface on a LAN between a network device (for example, a workstation or computer) and a medium attachment unit. Often used to describe a cable (in other words, the AUI cable attaches the workstation to the MAU). See also MAU and transceiver.
Automounter Part of Sun's Open Network Computing (ONC) architecture. Automounter works with Sun's Network File System (NFS) to automatically mount and dismount files on demand. See also NFS and ONC.
Backbone The main cable of a bus or tree LAN to which nodes or other LAN segments can attach.
Baseband A data communications medium (such as coaxial cable) used to carry data in many LANs. See also Broadband.
Batch A self-contained task that requires little or no operator input to run. Batch jobs are normally run as background tasks in most computers (in other words, no specific terminal or input devices are associated with it).
Baud A measurement of speed as sampled in seconds. Although baud is often interchanged with bits-per-second (bps), the two units of measurement are not necessarily the same. While bps always refers to bits, baud encompasses greater dimensions. If the sampling resolution is bits, then baud equals bps. If, however, the sampling is based on two bits, then baud and bps are not equal.
BCC Block check character. The result of a transmission verification algorithm performed on the block of data being transmitted. The one- or two-character result is normally appended to the end of the transmission. See also CRC and LRC.
Bell 103 AT&T modem that either originates or answers phone transmissions using asynchronous communications at speeds up to 300 bps.
Bell 113 Same as Bell 103, except the 113 modem can only originate or only answer (and not automatically switch between answering and originating).
Bell 201 AT&T modem providing synchronous data transmission at speeds up to 2400 bps.
Bell 202 AT&T modem providing asynchronous data transmission at speeds up to 1800 bps. Requires a four-wire line for full duplex operation.
Bell 208 AT&T modem providing synchronous data transmission at speeds up to 4800 bps.
Bell 209 AT&T modem providing synchronous data transmission at up to 9600 bps.
Bell 212 AT&T modem providing full duplex, asynchronous or synchronous data transmission at speeds up to 1200 on a dial network.
BSD Berkeley Software Distribution. Part of the University of Berkeley responsible for the on-going maintenance and distribution of Berkeley's version of UNIX.
BIOS Basic Input/Output System. In PCs, the BIOS is a central service loaded from ROM chips that provides the core services for accessing devices (for example, the monitor, keyboard, diskette, hard disk and so forth).
BISDN Broadband Integrated Services Data Network. An ISDN implementation that uses high-speed fiber-optic links. See also ISDN.
Bisync Binary Synchronous Communication. A byte-oriented protocol using synchronous transmission. Bisync was widely used by IBM before its transition to the bit-oriented SDLC protocol.
BIU Basic information unit. The SNA data format that consists of the RH and RU information. See also BLU.
BLU Basic link unit. The information contained in an SDLC frame that is composed of SDLC control data plus PIU plus SDLC control data. The PIU, in turn, is composed of the TH and BIU, with the BIU being the combination of RH and RU information.
BPR Business Process Re-Engineering. A method of restructuring business processes to achieve a greater level of automation, a more efficient flow of information throughout the business, and a better understanding of the critical business processes by its participants.
BRI Basic Rate Interface. The low-end interface of the Integrated Services Data Network (ISDN) that offers two 64-Kbps data/voice lines and a third 16-Kbps management circuit. See also ISDN and PRI.
bridge Normally a set of devices used to connect two remote networks, with each network unaware that the other network is, in fact, remote. Bridges operate on Layer 2 (data link layer) of the OSI model. They can be used to form WANs and differ from gateways and routers in that they do not perform any emulation or translation services. See also gateway and router.
Broadband A data communications medium (such as CATV cable) capable of transmitting voice, video and data simultaneously. See also baseband.
BSC Binary Synchronous Communication. See Bisync.
BTAM Basic Telecommunications Access Method. An IBM mainframe subsystem that handles application access and routing within the network. See also TCAM, RTAM and VTAM.
BTOS An UNIX-like operating system for the Unisys microcomputer line that originated from its Convergent Technology subsidiary. BTOS is a modified version of Convergent's own CTOS operating system. See also CTOS.
Bus topology A LAN topology that features a linear backbone on to which nodes are connected. See also tree topology, ring topology, and star topology.
CAD Computer aided design. Design and engineering processes aided by the use of computers. In most cases, CAD contributes to the initial design and test phases through the use of sophisticated design and modeling packages normally run engineering workstations.
CAM Computer aided manufacturing. Manufacturing processes aided by computers. With respect to manufacturing, CAM contributes in the area of process control and quality assurance.
CASE Computer aided software engineering. An approach to the development of application programming that uses other programs to help generate parts of (or all of) the final product. At a minimum, CASE might be thought of as a programming tool.
CBEMA Computer and Business Equipment Manufacturers Association. An association of U.S. manufacturers that, among other things, sponsors the X.3 standards committee of ANSI. See also ANSI and X.3.
CBX Computerized branch exchange. A telephone routing exchange driven by an intelligent device (in other words, a computer).
CCIR Consultative Committee for International Radio. An international standards body that sets the rules and requirements for radio communications. CCIR is a committee within the International Telecommunications Union (ITU). See also ITU and CCITT.
CCITT Consultative Committee for International Telegraphy and Telephony. An international standards body which sets the rules and requirements for international communications. CCITT is a committee within the larger International Telecommunications Union (ITU) and is best known for the development of the X.25 standard for public data networks. See also CCIR and ITU.
CCN Cluster controller node. See cluster controller.
CD Carrier Detect. A lead in the RS-232C interface that signals that information is being received over the data link. CD is also sometimes called Data Carrier Detect (DCD). In the full 25-pin RS-232C standard, CD is pin 8. In the abbreviated 9-pin PC interface, CD is pin 1. See also CTS, RS-232C and RTS.
CDE Common Desktop Environment. Part of the COSE agreement between major UNIX vendors to present a common interface to all UNIX implementations.
CGM Computer Graphics Metafile. A device-independent format for the presentation of graphics. Defined as ISO standard 8632.
CI Computer Interconnect. A high-speed, fault-tolerant connection between DEC VAX systems and a Star Coupler in VAXclusters. See also Star Coupler and VAXclusters.
CICS Customer Information Control System. An IBM transaction-oriented, database/data communications system for mainframes.
CIM Computer integrated manufacturing. A total solution to the computerization of manu-facturing operations that integrates as many related functions as possible (for example, administration, engineering, purchasing, and manufacturing).
CISC Complex (or complete) instruction set computer. The traditional architecture for computers in which useful software functions are supported by hardware. See also RISC.
CIXCD DEC's improved version of its basic CI link between VAX systems and Star Couplers in VAXclusters. The CIXCD is used with the VAX 9000 systems.
Classic HP applied the term Classic to its HP 3000 CISC models after it released its HP 3000 RISC models.
Cluster controller A device used to control the interface to multiple workstations. Cluster controllers are commonly used in remote locations to interface multiple workstations with a single data communications line. IBM cluster controllers (often referred to as CCNs) include the 3274 and 5294. Under SNA, a cluster controller is a PU 2 device.
CMIP Central Management Information Protocol. An OSI standard for the low-level functions required to perform network management. See also CMIS.
CMIS Central Management Information Service. An OSI standard for the high-level functions required to perform network management. See also CMIP.
CMS Conversational Monitor System. In an IBM mainframe environment, CMS is the interface between the user and the central Control Program (CP) of the VM operating system. Multiple copies of CMS are used to support multiple users (but still only one CP). See also CP.
coaxial In general, a cabling system that uses a central conducting core that is surrounded by an insulating medium that is, in turn, surrounded by a protective sheathing. Coaxial cable is used by IBM to connect its 3270 family of workstations. See also twinaxial.
COMMAND.COM A program supplied with MS-DOS and PC-DOS that performs the built-in DOS commands. For example, DIR and TYPE are internal commands, while FORMAT and COPY are external commands. All internal commands are contained within COMMAND.COM.
common communications support One of three SAA interfaces. The common communications support interface defines the data formats and protocols that can be used in an SAA environment. This includes, for example, the SNA 3270 data format, DIA/DCA and SNADS. See also common programming interface, common user interface, DCA, DIA, SAA, and SNADS.
common programming interface One of three SAA interfaces. The common programming interface defines a set of routines for accessing files, programs and communications devices under SAA. See also common communications support, common user interface, and SAA.
common user interface One of three SAA interfaces. The common user interface defines the characteristics of text and graphics screens generated by SAA-compliant programs and how the user interacts with those displays. See also common communications support, common programming interface, and SAA.
communications controller In an IBM mainframe environment, a communications controller is channel-attached to the host and serves to control the data communication network. IBM communication controllers (often referred to as either CUCNs or FEPs) include the 3705, 3725, and 3745. Under SNA, a communications controller is a PU 4 device. See also FEP and ICA.
compound document A document that can include text, graphics, video and voice data.
conditioning A process applied to standard analog phone lines to provide filtering in support of less error-prone data transmission. Various levels of conditioning are available at various costs and are implemented through specialized equipment.
connectionless A type of networking service in which the sending side requires no direct or indirect access to the receiving side(s).
connection-oriented A type of networking service in which the sending and receiving sides are in direct or indirect contact with one another.
CORBA Common Object Request Broker Architecture. A specification for the development of ORBs. CORBA establishes an environment for software objects to communicate with each other.
CP Control Program. In an IBM mainframe environment, CP is the central management facility under the VM operating system.
CPF Control Program Facility. An IBM operating system used on the System/38 computers.
CP/M An operating system for microcomputers created by Digital Research. CP/M was king of the hill among microcomputer operating systems prior to IBM's adoption of MS-DOS (PC-DOS).
cps Characters per second. A measurement of data communications speed and throughput.
CPU Central processing unit. The core processing unit of a computer system, in most cases contained in a single chip.
CRC Cyclic Redundancy Check. An error detection scheme in which the block check character (BCC) is derived from dividing all the serialized bits in a block by a predetermined binary number. See also BCC and LRC.
CSMA/CD Carrier Sense Multiple Access with Collision Detection. The LAN discipline (protocol) used by both Ethernet and the IEEE 802.3 standard. Under CSMA/CD, a device that wishes to transmit on the network first listens for other activity. If the network is quiet, the device then attempts to transmit. Data collisions are detected and result in both transmitters retrying their transmissions after a random amount of time.
CSU Channel service unit. The interface to a Digital Data Service line. The CSU takes data off the DDS line and feeds it to a Data Service Unit (DSU) that, in turn, interfaces with the terminal or computer equipment. In many cases, a CSU is combined with a DSU, into a single unit called an integrated service unit (ISU). See also DDS, DSU, and ISU.
CTERM A DECnet protocol used by one DEC host to forward information from a terminal to another host. This is the protocol used by the standard DECnet SET HOST command.
CTOS An operating system produced by Convergent Technology (Unisys) for its line of microcomputers. CTOS is a multitasking, multiuser operating system that is similar in structure to UNIX.
CTS Clear to Send. A lead in the RS-232C interface. CTS is raised in response to receipt of the Request to Send (RTS) signal. In brief, when one side of the link wishes to transmit, it raises the RTS line. If the other side is ready to receive, it responds by raising the CTS line. Once transmission has begun, the Carrier Detect (CD) line is also raised. In the full 25-pin RS-232C standard, CTS is pin 5. In the abbreviated 9-pin PC interface, CTS is pin 8. See also CD, RS-232C, and RTS.
CTS-300 DEC's commercial operating system for the PDP-11 family of computers. See also DSM-11, RSTS, and RSX.
CUCN Communications controller node. See communications controller.
CUT Control unit terminal. Another term used by IBM for its general-purpose workstations.
DAP Data Access Protocol. A low-level DECnet protocol responsible for the movement of information from system to system.
DARPA Defense Advanced Research Project Agency, formerly known as ARPA. An agency within the U.S. Department of Defense that was instrumental in the development of TCP/IP. The agency's ARPANET network was the precursor of the modern Internet. See also TCP/IP.
DASD Direct access storage device. An IBM term that refers to IBM mass storage devices (disk drives).
Data Link Layer The second (from the bottom) layer of the OSI Reference Model. The Data Link layer defines the protocols used to move data across the Physical Layer (for example, HDLC, LAP-B or IEEE 802.2). The Data Link Layer is sometimes also called the Logical Link Layer. See also OSI Reference Model.
DB2 IBM's relational database for mainframes running the MVS or VM operating systems.
DCA Document Content Architecture. An IBM document specification that defines the structure and contents of documents in both revisable and final forms. Under DCA, revisable documents include their editing history, while final form documents are the net result of all edits.
DCD Data Carrier Detect. See CD.
DCE Data communications equipment. A device such as a modem that facilitates a data communications link. The DCE interfaces with the data terminal equipment (DTE), which is the origin or destination of the information. A complete link includes a DTE interfacing with a DCE that interfaces with another DCE that, in turn, interfaces with another DTE. In direct connection environments, one side of the connection (normally the computer) emulates a DCE interface. See also DTE.
DDCMP Digital Data Communications Message Protocol. A DECnet byte-oriented protocol that ensures the integrity and correct sequencing of messages between adjacent nodes. DDCMP can be used for synchronous or asynchronous transmissions and is most frequently used to implement DECnet wide-area connections over conventional leased lines.
DDM Distributed Data Management. An IBM product geared for its mid-range machines. DDM enables a system to access remote files over a network at both the record and the file level. See also DIA and SNADS.
DDN Defense Data Network. The multivendor WAN used by the U.S. Department of Defense.
DDS Digital Data Service. A leased line using digital transmission that can provide data communications rates up to 56 Kbps. When DDS is employed, the modems used with analog lines are replaced by a Channel Service Unit (CSU) and a Data Service Unit (DSU). See also CSU and DSU.
DEBNA Digital Ethernet VAXBI Network Adapter. Replaced by the DEBNI. See DEBNI.
DEBNI Digital Ethernet VAXBI Network Interface. A DEC controller card for VAX computers that interfaces the VAXBI bus with the Ethernet LAN. The DEBNI replaced the DEBNA. See DEBNA.
DEC Digital Equipment Corporation.
DECmate An office automation (word processing) microcomputer.
DECnet Digital's line of products that allow communications between DEC systems.
DECnet-DOS A DEC software product for PCs and PS/2s running MS- DOS (or PC-DOS). DECnet-DOS enables the PC to participate in a DECnet network (normally through a Ethernet adapter in the PC). The functions provided by DECnet-DOS include task-to-task communications, remote file access and VT 220 terminal emulation.
DECnet/SNA Gateway A LAN-attached gateway between SNA and DECnet. The IBM side of the gateway might attach via an SNA SDLC connection or via a direct channel attachment to a mainframe. Specific SNA services are run in other DEC hosts to provide functional services across the gateway (such as terminal access, file transfer and document exchange). See gateway.
DECrouter LAN-attached bridges to facilitate wide-area connections within DECnet networks. A router can be used to connect two Ethernet LANs using DDCMP or X.25. A router on one LAN can communicate with another router or with an integrated communications card within a DEC host system.
DECserver Digital's LAN terminal server. See terminal server.
DECstation Digital's line of PCs based on Intel processors and their line of engineering workstations based on RISC technology. The DECstation 3100 and 5000 use a RISC design while the DECstation 200, 300, and 400 models use standard PC architectures. See also VAXstation.
DECwindows DEC's architecture for a graphical user interface that provides a common, multiwindowed graphical environment from which the end user can access applications residing on other systems. DECwindows is part of DEC's Network Application Support (NAS). See also NAS.
DELNI Digital Ethernet Local Network Interconnect. Provides connection to eight Ethernet segments with a ninth connection that can be used to optionally attach the DELNI to the LAN backbone. The DELNI can be used as a stand-alone device to create a small DECnet network, or can be networked into a main LAN as described.
DELQA Digital Ethernet LAN-Q-bus Adapter. A DEC controller card for Q-bus computers that interfaces the computer with the Ethernet LAN. The DELQA replaces the DEQNA.
DELUA Digital Ethernet LAN-Unibus Adapter. A DEC controller card for Unibus computers that interfaces the computer with the Ethernet LAN. The DELUA replaces the DEUNA.
DEMCA Digital Ethernet MicroChannel Adapter. An Ethernet ThinWire adapter card for PS/2 computers. DEMCA uses a standard MCA slot.
DEMPR Digital Ethernet Multi-Point Repeater. A DEC LAN product that provides eight ThinWire ports, with a ninth port to optionally connect to the standard Ethernet cable. Like a DELNI, a DEMPR can be used to implement a standalone ThinWire LAN or to integrate ThinWire devices into a main Ethernet LAN.
DEPCA Digital Ethernet PC Adapter. An Ethernet ThinWire adapter card for PCs. DEPCA uses a standard 8-bit PC slot.
DEQNA Digital Ethernet Q-bus Network Adapter. The DEQNA was replaced by the DELQA. See DELQA.
DeskManager HP's electronic mail and office automation product for the HP 3000 computer.
DESPR Digital Ethernet Single-Port Repeater. A DESPR provides conversion between an Ethernet transceiver connection and a ThinWire connection. A DESPR is used to attach a ThinWire device to a standard Ethernet transceiver. See also DESTA.
DESTA Digital Ethernet Station Adapter. A DESTA provides conversion between a ThinWire connection and an Ethernet transceiver. A DESTA is used to attach a standard Ethernet device into a ThinWire network. See also DESPR.
DESVA Digital Ethernet MicroVAX 2000 Adapter. A DEC controller card for the MicroVAX 2000 that interfaces the computer with the Ethernet LAN.
DEUNA Digital Ethernet Unibus Network Adapter. The DEUNA was replaced by the DELUA. See DELUA.
DHCF Distributed Host Command Facility. An IBM product running as a remote processor, DHCF interfaces with the mainframe-resident HCF subsystem to provide distributed access. In a pure IBM environment, it is often used to gain 3270 terminal access from a mainframe to a remote, nonmainframe system. In the multivendor arena, DHCF is often emulated to allow 3270 terminals to access the non-IBM system via the mainframe HCF facility.
DIA Document Interchange Architecture. One of three distribution techniques used by IBM to move information from system to system in an SNA network. DIA is specifically focused on the movement of documents in both revisable and final form. See also DCA, DDM and SNADS.
digital transmission. Transmission in which information is sent in its discrete bit form. That is, each bit is represented as a 0 or a 1. See also analog transmission.
DISOSS Distributed Office Support System. An IBM product that enables documents created by different products to be distributed and shared among IBM systems. DISOSS is commonly used as an interface point for transmitting documents to and from non-IBM computers.
DMA Direct Memory Access. A hardware method of reading and writing directly to memory without involving the main CPU.
DNA Digital Network Architecture. DEC's architecture for the interconnection of its computer and computer-related devices. This is equivalent to IBM's SNA, HP's AdvanceNet, and Sun's ONC.
DoD U.S. Department of Defense. See also DARPA.
Domain 1. A set of hosts on a LAN that share a single database, typically for moving mail between hosts. 2. The name for Apollo's (now HP's) line of engineering workstations. See also Apollo.
DOS Disk Operating System. Introduced in 1981 by Microsoft Corp. as the operating system for IBM's 8080-based IBM PC.
DOS/VS Disk Operating System/Virtual Storage. An IBM System/370 architecture operating system.
DOS/VSE Disk Operating System/Virtual Storage Extended. An IBM System/370 architecture operating system.
dpi Dots per inch. A term used to describe the resolution of printers. Most dot-matrix printers offer less than 200 dots per inch resolution, while most laser or inkjet printers offer at least 300 and as high as 1,200 dots per inch. The higher the density of dots, the better the resolution of printed characters, graphics and images. In contrast, typesetting equipment can offer dpi resolution of 1,270, 2,540, and even higher amounts.
DS/1000 and DS/3000 HP 1000 and HP 3000 networking services that have been replaced by NS/1000 and NS/3000. The DS services relied mostly on HP HDLC links for networking, while the NS products use standard IEEE 802.3 links.
DS0 Digital Service rate 0. The transmission rate (64 Kbps) of each of the 24 circuits in a T1 connection. See also T1.
DS1 Digital Service rate 1. The combined transmission rate (1.544 Mbps) of all 24 circuits in a T1 connections. See also T1.
DSM-11 DEC's business-oriented operating system for the PDP/11 series computers. See also CTS-300, RSTS, and RSX.
DSR Data Set Ready. A lead in the RS-232C interface, DSR is used to signal that the modem (or DCE device) is ready for communications. The counterpart to DSR is Data Terminal Ready (DTR), which is the computer/terminal's signal that it is ready to communicate. In most cases, no communication can take place unless both the DSR and DTR signals are raised. In the full 25-pin RS-232C standard, DSR is pin 6. In the abbreviated, 9-pin PC interface, DSR is pin 4. See also DTR and RS-232C.
DSU Data service unit. A device that interfaces between a channel service unit (CSU) and a terminal or computer. The DSU and CSU work together to interface the computing device to a digital data service (DDS). See also CSU, DDS, and ISU.
DTC Distributed terminal controller. For the RISC-based HP 3000 systems, DTCs are used to interface the asynchronous terminals into the LAN-based system. See also ADCC and ATP.
DTE Data terminal equipment. A device such as a terminal or computer that is the origin or destination of information flowing over a data communications link. The DTE interfaces with data communication equipment such as a modem, that handles the actual data communications processing and interfaces with another DCE device (that interfaces with another DTE device). When direct connect links are used, one side emulates a DCE while the other performs normal DTE functions. See also DCE.
DTP Distributed Transaction Processing. An OSI upper-layer service for implementing transaction-based processing. Defined as ISO standard 10026.
DTR Data Terminal Ready. A lead in the RS-232C interface. Data Terminal Ready is used to signal to the modem (or DCE device) that it is ready for communications. The counterpart to DTR is Data Set Ready (DSR), which is the modem's signal that it is ready to communicate. In most cases, no communication can take place unless both the DTR and DSR signals are raised. In in-dial situations, DTR is normally raised when the Ring Indicator (RI) is raised to tell the modem to answer the phone. In the full 25-pin RS-232C standard, DTR is pin 20. In the abbreviated, 9-pin PC interface, DTR is pin 4. See also DSR, RI, and RS-232C.
Duplex See half duplex and full duplex.
EBCDIC Extended Binary Coded Decimal Interchange Code. A definition for the bit compositions of characters and symbols. EBCDIC uses 256 eight-bit patterns to define 256 different characters, numbers and symbols. IBM mid-range and mainframe systems use the EBCDIC standard. See also ASCII.
ECMA European Computer Manufacturers Association. A standards organization composed of European computer manufacturers. ECMA participates in both CCITT and ISO activities.
ECMA 40 ECMA specifications for HDLC frame structure. See also HDLC.
ECMA 49 ECMA definition of HDLC elements of procedures. See also HDLC.
ECMA 60 ECMA definition of HDLC unbalanced class of procedures. See also HDLC.
ECMA 61 ECMA definition of HDLC balanced class of procedures. See also HDLC.
ECMA 71 ECMA standard for transport protocol (for ISO/OSI layer 4).
ECMA 80-82 ECMA definitions of the physical and logical link control for CSMA/CD. See also CSMA/CD.
EDI Electronic data interchange. A set of services for information and document exchange. The intent of EDI is to reduce or eliminate paper flow for common business transactions.
EIA Electronic Industries Association. A U.S. trade organization specializing in the electrical and functional characteristics of interface equipment. EIA has a close working relationship with ANSI.
EISA Extended Industry Standard Architecture. An alternative to IBM's MCA bus structure for the PS/2. EISA was developed by a group of nine manufacturers led by Compaq Computer. See also MCA.
EMA Enterprise Management Architecture. DEC's products and services that implement network management.
EMI Electromagnetic Interference. Electromagnetic waves that can potentially interfere with the operation of electronic devices. The U.S. Federal Communication Commission (FCC) is responsible for deciding whether an electronic device (such as a computer) generates too much EMI or radio frequency interference (RFI). See also FCC and RFI.
end node A node in a network that cannot forward or reroute packets intended for other nodes. See also node.
ESDI Enhanced Small Device Interface. A disk interface standard that offers storage of 34 sectors per cylinder. Because of its speed and density, ESDI is used in both PCs and mid-range systems. See also MFM, RLL, SCSI, and ST506.
Ethernet A LAN standard that uses the Carrier Sense, Multiple Access with Collision Detection (CSMA/CD) discipline. Ethernet was originally developed by Xerox Corporation. See also IEEE 802.3.
EU End User. An IBM SNA term.
FAL File Access Listener. FAL is a DECnet module that listens for network requests to access its local files. In effect, FAL is a network file server for DECnet.
Fast Ethernet See 100BASET.
FCC Federal Communications Commission. An agency of the U.S. government that regulates the use of electromagnetic waveforms, such as television waves, radio waves and other electronic and magnetic emissions. See also EMI and RFI.
FDDI Fiber Distributed Data Interface. FDDI is an ANSI standard for fiber-optic networking. FDDI uses a token-passing discipline over a ring topology at speeds up to 100 Mbps. Interfaces to traditional LANs enable the FDDI network to act as a WAN or MAN for the LANs attached to it. See also MAN and WAN.
FEP Front-end processor. A phrase often used to refer to intelligent communications controllers. See also communications controller.
Fibre Channel. A high-speed architecture for connecting network devices and high-speed hardware. Sometimes seen as a replacement for HiPPI.
FIPS Federal Information Processing Specification. Specifications adopted and published by the U.S. government that are mandated for use by the government and its agencies.
FIPS 1-1 FIPS code for information interchange.
FIPS 7 Implementation of FIPS 1-1 and related standards.
FIPS 15 Subsets of the FIPS 1-1 code for information interchange.
FIPS 16-1 Bit sequencing of the FIPS 1-1 code for serial transmissions.
FIPS 17-1 Character and parity structure for FIPS 1-1 transmissions.
FIPS 35 Code extension techniques using 7 or 8 bits.
FIPS 71 Advanced Data Communication Control Procedures (ADCCP). See also ADCCP.
Firewire See IEEE 1394.
fractional T1 One or more of the 24 64-Kbps channels of a T1 line, broken out by the local telephone office and offered to local customers. Fractional T1 enables a range of customers to share the benefits (and cost) of a full T1 line. See also T1.
frame A block of information organized in a specific format. Depending on the network, a frame might have origin and destination information in it, or might be included as part of another structure (such as a packet) that defines the routing information. See also packet.
FTAM File Transfer, Access and Management. An OSI upper-level service for file transfer between open systems. FTAM is defined as OSI standard 8571.
FTP File Transfer Protocol. FTP is a TCP/IP application that enables the transfer of files between host computers.
FTSC Federal Telecommunications Standards Committee. A U.S. government advisory body to the National Communications System agency.
FTSC 1003 FTSC definition of synchronous data link control procedures (ADCCP). See also ADCCP.
FTSC 1005 FTSC definition of coding and modulation requirements for 2,400-bps modems.
FTSC 1006 FTSC definition of coding and modulation requirements for 4,800-bps modems.
FTSC-1007 FTSC definition of coding and modulation requirements for 9,600-bps modems.
FTSC-1008 FTSC definition of coding and modulation for 600/1200-bps modems.
FTSC 1010 FTSC definition of bit sequencing the ANSI X3.4 information code for serial transmissions.
FTSC 1011 FTSC definition of character and parity structure for ANSI X3.4 transmissions.
Full duplex Simultaneous, independent bidirectional transmission.
FUNI Frame User Network Interface. A service that performs protocol conversion between Frame Relay and ATM networks.
Gabriel A software product that detects the presence of SATAN. See also SATAN.
Gateway A device that permits the network activity on one type of network to flow into another type of network. A gateway is different from a bridge or router in that it must perform conversion and/or emulation tasks to tie two (or more) heterogeneous networks together, while bridges and routers link two homogenous networks. A gateway maps to all seven layers of the OSI model. See also bridge and router.
GCS Group Control System. In an IBM mainframe environment, GCS is used with the VM operating system to host SNA-oriented subsystems such as ACF/VTAM.
GOSIP Government OSI Profile. A set of requirements issued by the U.S. and United Kingdom governments to dictate the use of OSI-compliant products within the government and its agencies.
GPI Graphics Programming Interface. A generalized interface within OS/2 controlling fonts and graphics as displayed and printed on a variety of devices.
Groupware A type of software that facilitates sharing of electronic data and processes throughout a group of end users.
GUI Graphical user interface. A term used to describe a graphical interface as seen by the end user of a computer system. Specifically, a GUI enables a user to select applications by selecting icons and graphics representations presented on the screen. GUI products include the Apple operating system, Microsoft Windows, the OS/2 Presentation Manager, HP's NewWave and DEC's DECwindows.
H4000 and H4005 See transceiver.
half duplex Transmission in one of two directions at any given time, but not both directions simultaneously.
HASP Houston Automatic Spooling Program. An IBM Job Entry Subsystem (JES) for the OS/SVS operating system.
HCF Host Command Facility. An IBM package originally designed to interface mainframes with 8100 Information Processing machines running the companion DHCF package. HCF is commonly used as an interface from IBM to non-IBM computers. See also DHCF.
HDLC High-Level Data Link Control. A bit-level protocol for data transmission. HDLC is ISO's implementation of the IBM SDLC standard. HDLC is often used as a high-speed, general-purpose computer-to-computer link.
heartbeat A function performed by transceivers on Ethernet and 802.3 IEEE networks that signals their continuing operation.
High Performance Routing (HPR) A mechanism used in IBM networks to provide an SNA/APPN network with native access to a wide-area ATM network.
HiPPI (High Performance Parallel Interface) A method for connecting heterogeneous supercomputers with IBM mainframes.
HP Hewlett-Packard Company.
HP 125 HP's implementation of a combined terminal and PC system. The HP 125's memory capacity was, however, rather limited.
HP 150 HP's revised implementation of a dual terminal and personal computer. The HP 150 also featured touch-screen operation.
HP 700 A monochrome HP terminal.
HP 1000 HP's line of real-time technical minicomputers. The HP1000s use a proprietary CISC architecture.
HP 2620 A monochrome HP terminal.
HP 2640 A monochrome HP terminal.
HP2697 A color HP terminal.
HP 3000 HP's line of general-purpose business computers. The HP 3000 product line includes both CISC and RISC models. The CISC models include the MICRO 3000 and Series 70. The RISC models include the HP 3000 Series 900 Series.
HP 9000 HP's line of engineering workstations. The HP 9000 line includes both RISC and CISC models.
HP-GL Hewlett-Packard Graphics Language. The command set used by HP plotters. HP-GL is a vector-oriented interface that describes the objects to be printed/plotted as a series of mathematical shapes. HP-GL also supports color. Because of its widespread use, HP-GL is often used as an intermediary format for converting graphics from one system (or package) to another.
HP-IB HP's implementation of the IEEE 488 general-purpose, bus interface used to interface tape and disk drives to system processors.
HP Portable The HP Portable and HP Portable Plus were HP's initial MS-DOS, portable PC offerings. Unfortunately, they lacked such things as built-in disk or diskette drives.
HP-UX HP's UNIX implementation for the HP 9000 Series computers.
HSC Hierarchical Storage Controller. A DEC device that allows shared access to a set of disk drives. The HSC is used in VAXclusters to act as the intermediary between a Star Coupler and the drives. See also CI, Star Coupler, and VAXcluster.
ICA Integrated Communications Adapter. An IBM device used in a 9370 and 4300 Series mainframes as a communications controller. For the 4300, an ICA is an alternative to a stand-alone 3705 or 3725 communications controller.
ICMP Internet Control Message Protocol. ICMP is responsible for the detection and reporting of link-level errors.
IEEE Institute of Electrical and Electronics Engineers. A professional society that often participates in the development of standards. IEEE recommendations are usually forwarded to ANSI for its endorsements. Among the best known IEEE standards are the 802.2, 802.3, and 802.5 LAN specifications.
IEEE 488 A general-purpose bus interface most commonly used to interface tape and/or disk drives to system processors.
IEEE 802.2 A standard that defines the Logical Link Control (LLC) level of LAN communications. IEEE 802.2 is used with the 802.3, 802.4 and 802.5 medium access control (MAC) standards. In terms of layers, 802.2 resides above the MAC standards.
IEEE 802.3 A standard that defines the medium access control (MAC) layer for a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) bus network. The IEEE 802.3 standard is not identical to Ethernet; however, both Ethernet and 802.3 devices can coexist on the same cable. The IEEE 802.3 standard has been adopted by ECMA as ECMA-80, 81 and 82 and by ISO as ISO 8802/3. See also Ethernet, ECMA and ISO.
IEEE 802.4 A standard that defines the medium access control (MAC) layer for a token-passing bus network.
IEEE 802.5 A standard that defines the medium access control (MAC) layer for a token-passing ring network. IBM's Token Ring conforms to this standard.
IEEE 802.6 A standard defining a MAN based on a fiber-optic ring 30 miles in length. The standard supports data rates of 1.5 Mbps to 155 Mbps.
IEEE 902.9a A standard for running two networks over 10BaseT wiring. See also isochronous Ethernet.
IEEE 1003 IEEE definition of portable operating systems (POSIX). See also POSIX.
IEEE 1394 A local device interface for ATM or Fast Ethernet, which permits either to be routed to individual devices. See also Firewire.
IMF/3000 and IMF II/3000 HP 3000-based software that provides interactive (virtual terminal and batch) capability with an IBM mainframe. IMF/3000 uses bisynchronous com-munications, and IMF II/3000 uses SNA SDLC communications. IMF II is also known as SNA IMF.
INP Intelligent Network Processor. An intelligent HP controller card for the HP 3000 CISC computers that provides bisynchronous, SDLC, and X.25 communications.
Internet Interoperability Object Protocol (IIOP). A part of the CORBA 2.0 specification that adds multivendor connectivity to the ORB model.
IP Internet Protocol. See TCP/IP.
IPC Interprocess communications. A mechanism that enables two programs to communicate with one another. The term Net-IPC is often used to describe a network-level interface between two programs. See also API, APPC, and RPC.
IPX A datagram protocol established by Novell for use in sending data over Netware networks. In the OSI model, IPX is a network-layer protocol. See also NetWare.
ISA Industry standard architecture. A term used to describe the original bus structure used in the PC/AT and subsequently adopted by the industry as a de facto standard. See also EISA and MCA.
ISDN. Integrated Services Digital Network. A digital-based network for voice and data lines. From a broader perspective, ISDN is targeted to be an international service for the integration and networking of voice and digital information.
ISO International Standards Organization. A voluntary, independent organization chartered to define international standards for communications of all types. ISO is best known for the development of the seven-layer Basic Reference Model for Open Systems Interconnection, termed the OSI Model. See also OSI Reference Model.
ISO 646 ISO definition of a seven-bit character set.
ISO 1155 ISO standard for the use of longitudinal parity for error detection.
ISO 1177 ISO structure for asynchronous (start/stop) and synchronous transmission.
ISO 1745 ISO basic mode control procedures.
ISO 2022 Code extension techniques based on the ISO 646 seven-bit character set.
ISO 2110 ISO definition of a 25-pin DTE/DCE connector and pin assignments. See also RS-232C.
ISO 2111 ISO basic-mode control procedures for code-independent information transfer.
ISO 2628 Complements to the ISO 2111 basic mode control procedures.
ISO 2629 ISO basic mode control procedures for conversational information message transfer.
ISO 3309 ISO definition of HDLC frame structure. See also HDLC.
ISO 4335 ISO definition of HDLC elements of procedures. See also HDLC.
ISO 4902 ISO definition of 37-pin and 9-pin DTE/DCE connectors and pin assignments. See also RS-232C and RS-449.
ISO 6159 ISO definition of HDLC unbalanced class of procedures. See also HDLC.
ISO 6256 ISO definition of HDLC balanced class of procedures. See also HDLC.
ISO 7498 The ISO Open Systems Interconnect basic Reference Model.
ISO 8072 Transport layer definitions for the OSI Reference Model.
ISO 8073 Transport layer connection-oriented services for the OSI Reference Model.
ISO 8208 ISO standard for X.25 packet level protocol.
ISO 8326-27 Session Layer connection-oriented services for the OSI Reference Model.
ISO 8348 Network Layer definitions for the OSI Reference Model.
ISO 8473 Network Layer connectionless services for the OSI Reference Model.
ISO 8571 ISO definition of the File Transfer, Access and Management (FTAM) application. See also FTAM.
ISO 8602 Transport Layer connectionless services for the OSI Reference Model.
ISO 8613 ISO definition of Office Document Architecture (ODA). See also ODA.
ISO 8632 ISO definition of Computer Graphics Metafile (CGM). See also CGM.
ISO 8648 Network Layer internal organization in the OSI Reference Model.
ISO 8802/2 ISO standard for class 1 logical link control.
ISO 8802/3 ISO's equivalent of the IEEE 802.2 and 802.3 standards for a CSMA/CD LAN. See also IEEE 802.2 and IEEE 802.3.
ISO 8802/4 ISO's equivalent of the IEEE 802.2 and 802.4 standards for a token-passing bus LAN. See also IEEE 802.2 and IEEE 802.4.
ISO 8802/5 ISO's equivalent of the IEEE 802.2 and 802.5 standards for a token-passing ring LAN. See also IEEE 802.2 and IEEE 802.5.
ISO 8822-23 Presentation Layer connection-oriented services for the OSI Reference Model.
ISO 8832-33 ISO definition for Job Transfer and Manipulation application (JTM). See also JTM.
ISO 8878 ISO standard for the use of X.25 as a connection-oriented service.
ISO 8886 Data-Link Layer definitions for the OSI Reference Model.
ISO 9040 ISO definition of the Virtual Terminal Services (VTS) application. See also VTS.
ISO 9314 ISO standard for Fiber Distributed Data Interface (FDDI). See also FDDI.
ISO 9548 Session Layer connectionless services for the OSI Reference Model.
ISO 9576 Presentation Layer connectionless services for the OSI Reference Model.
ISO 9594 ISO standard for directory services based on the CCITT X.500 standard. See also X.500.
ISO 9595-96 ISO definition of network management applications (CMIS and CMIP). See also CMIS and CMIP.
ISO 10020/21 ISO standard for message handling services based on the CCITT X.400 standard. See also X.400.
ISO 10026 ISO standard for Distributed Transaction Processing (DTP). See also DTP.
Isochronous Ethernet See IEEE 902.9a.
ISU Integrated Service Unit. The combination of a channel service unit (CSU) and data service unit (DSU) into one device. The ISU is used to interface computers and terminals to a digital data service (DDS) line. See also CSU, DDS, and DSU.
ITU International Telecommunications Union. The ITU is an agency under the United Nations charged to define standards for international telecommunications. The CCITT is a committee of the ITU. See also CCITT.
IX Interactive Executive. An IBM implementation of UNIX that runs as a guest operating system under the VM operating system on mainframes.
JCL Job Control Language. An IBM term for the instructions used to control execution within a Job Entry Subsystem (JES). JCL is also often used as a general term for the instructions required to define a sequence of events to be run on a computer.
JES. Job Entry Subsystem. A specific IBM Job Entry Subsystem for the OS/VS1 operating system that is also known as JES1 and RES. In more general terms, a job entry subsystem controls the batch job environment and, as part of that environment, collects information from Remote Job Entry (RJE) workstations and distributes information to RJE workstations.
JES1 Job Entry Subsystem version 1. An IBM Job Entry Subsystem (JES) for the OS/VS1 operating system. See JES.
JES2 Job Entry Subsystem version 2. An IBM Job Entry Subsystem (JES) for the MVS operating system. See JES.
JES3 Job Entry Subsystem version 3. An IBM Job Entry Subsystem (JES) for the MVS operating system. See JES.
job In general, a specific task or set of tasks associated with a given user or application. See also Batch.
JTM Job Transfer and Manipulation. An OSI upper-layer service for the transfer and sharing of jobs between open systems. Defined as ISO standard 8832/33.
Kbps Kilobits per second. 1,024 bits per second (approximately 128 bytes per second).
KBps Kilobytes per second. 1,024 bytes per second (approximately 8,192 bits per second).
Kermit A file transfer protocol developed by Columbia University in the city of New York and often used to transfer files between PCs and mid-range computers. In most implementations, Kermit also includes terminal emulation. Kermit was indeed named after the Muppet.
LAN Local Area Network. A communications architecture that passes information between multiple systems over relatively short distances at very high speeds.
LANIC Local Area Network Interface Controller. An HP controller card that interfaces the HP 1000 and HP 3000 to an 802.3 LAN.
LanWorks A set of products jointly developed by DEC and Apple Computer that enable VAX and Macintosh systems to share files, printers, documents and mail in a common network. Later combined into PathWorks.
LAP-B Link Access Balanced, revision B. CCITT's implementation of a balanced, bit-oriented protocol based on the IBM SDLC standard. LAP-B is most widely known as the protocol of choice to connect a computer to a packet-switching X.25 network.
LAT Local Area Transport. An Ethernet-based DEC protocol implemented for terminal servers to enable terminals connected to a server to establish logical sessions on DEC host nodes without connecting through intervening host nodes (as in the case of a SET HOST command). LAT also attempts to minimize network usage by grouping individual characters into a single transmission. See also CTERM and terminal server.
LAVC Local Area Vaxcluster. A DEC VAXcluster solution that uses standard LAN connections to share access to a set of disk drives between multiple VAX systems.
LDAP Lightweight Directory Access Protocol. A subset of the X.500 standard designed for interoperability and ease of use. LDAP and X.500 provide the means to create a universal network directory system.
Leased line A permanent circuit provided by the telephone company (or similar organization). A leased line can be a direct point-to-point connection or a multipoint connection. Leased lines are available for either analog (voice grade) or digital transmission. Analog lines can also be conditioned to reduce errors. See also conditioning.
LEN Low-Entry Networking. An IBM standard that enables adjacent nodes to initiate and terminate communications with one another using LU 6.2 APPC.
LLC Logical Link Control. The highest sublayer in Layer 2 (data link layer) of the OSI model. In the IEEE standards, 802.2 is the LLC. In Ethernet, the LLC and the medium access control (MAC) are enmeshed. See also MAC and OSI Reference Model.
LocalTalk Apple Computer's cabling for the AppleTalk LAN.
Location Broker Part of HP/Apollo's Network Computing System (NCS) architecture. Global and Local Location Brokers determine what local services will be available on a network-wide basis. See also NCS.
logical unit See LU.
LRC Longitudinal redundancy check. An error detection scheme in which a check character is generated on the basis of the exclusive OR of all the characters in the block. See also BCC and CRC.
LSI Large Scale Integration. An approach to printed circuit board design that uses a small number of individual components (chips), with each component being responsible for a range of functions. See also VLSI.
LU Logical unit. Logical units are part of the IBM SNA structure and correspond to entities (for example, users, programs) that request or transmit information through the network.
LU Type 0 (LU 0) Direct-link communications.
LU Type 1 (LU 1) Data processing workstation communications.
LU Type 2 (LU 2) 3270-type workstation communications.
LU Type 3 (LU 3) 3270-type printer communications.
LU Type 4 (LU 4) 5250-type printer communications.
LU Type 6.1 (LU 6.1) Program-to-program communications using one of the following SNA data stream formats: character string, 3270, logical messages services, or user-defined.
LU Type 6.2 (LU 6.2) Program-to-program communications using either the SNA general data stream format or a user-defined data stream.
LU Type 7 (LU 7) 5251-type workstation communications.
LUNI LAN Emulation User-to-Network Interface. Part of the ATM Forum's LAN Emulation Over ATM specification, which enables multivendor end stations to communicate with an ATM network.
MAC medium access control. The lower level of LAN communications that handles discipline and topology of the LAN. MAC corresponds to the Physical Layer (layer 1) of the OSI Reference Model. See also LLC and OSI Reference Model.
MACH A multiuser, multitasking operating system directly descended from UNIX that offers lower overhead and higher performance than UNIX.
MAN Metropolitan area network. A somewhat smaller, special implementation of a WAN. MANs use fiber-optic transmissions to provide high-speed communications over relatively small distances (but distances that are beyond the range of a traditional LAN). See also FDDI and WAN.
MAP Manufacturing Automation Protocol. A transport system defined by the manufacturing industry to accommodate its specific needs and requirements.
MAPI Messaging Application Programming Interface. A proprietary protocol created by Microsoft that permits developers to create mail-enabled applications.
MAU Medium attachment unit. A device that physically attaches to a LAN to permit the connection of one or more devices (or LAN segments) to that LAN via an AUI. See also transceiver and AUI.
Mbps Megabits per second. 1,048,576 bits per second (approximately 131,072 bytes per second).
MBps Megabytes per second. 1,048,576 bytes per second (approximately 8,388,608 bits per second).
MCA Micro Channel Architecture. IBM's improved, proprietary architecture for the PS/2 that replaced the bus architectures used in the original PC/XT and PC/AT.
MCP Master Control Program. The operating system for the Burroughs line of Unisys computers.
MFM Modified frequency modulation. A disk encoding technique that results in 17 sectors per cylinder. MFM is the original (and still widely used) encoding technique for PC disk drives and uses the ST-506 interface. See also ESDI, RLL, SCSI, and ST-506.
MFT Multiprogramming with a Fixed number of Tasks. An IBM System/360 architecture operating system.
MHz One million cycles per second. The usage of MHz has dramatically increased since its associated with PCs. In that arena, the higher the MHz, the faster the processor can operate (because there are more available cycles per second).
MicroVAX The low end of DEC's VAX line. The MicroVAX line includes the MicroVAX 2000, MicroVAX II, and MicroVAX 3000 series.
MicroVMS DEC's implementation of the VMS operating system for the MicroVAX computers.
Millisecond One thousandth of a second.
MIPS Million instructions per second. A unit of measurement applied to the performance of computer systems. For example, a computer rated at 3 MIPS can perform 3 million instructions in one second. The higher the MIPS rating, the higher the performance.
modem Modulator-Demodulator. A device that converts between the digital data format used by computers and the analog signals transmitted over a telephone circuit.
MPE MultiProgramming Environment. HP's operating system for the HP 3000 Series computers. Note that a special version of MPE (MPE-XL) runs on the HP 3000 RISC systems.
MPOA Multiple Protocols Over ATM. An extension of the LAN emulation concept, used to map network layer addresses--such as IP or IPX--to ATM.
MRJE/1000 and MRJE/3000 HP 1000- and HP 3000-based software products that provide bisynchronous multileaving RJE support to IBM mainframes.
MS-DOS Microsoft Disk Operating System. An operating system acquired and modified by Microsoft Corporation for use in microcomputers.
MS Windows Microsoft Windows. Microsoft's graphical user interface (GUI) that enables the user to select from multiple on-screen applications, each application occupying a screen window. See also GUI.
MTA Message Transfer Agent. In an X.400 network, the MTA forwards messages between User Agents (UA) or among other Message Transfer Agents. See also MTS, UA, and X.400.
MTBF Mean time between failure. The length of time (on average) a unit should operate without failures.
MTS Message Transfer System. The network of routes available between Message Transfer Agents in an X.400 electronic mail network. See also MTA and X.400.
MTTR Mean time to repair. The amount of time (on average) it should take to repair a specific failure.
multidrop A connection enabling multiple devices to share one physical line. This is often used in the context of a data communications line that has multiple terminals attached to it. See also multipoint.
multipoint A connection between multiple devices that enables all attached devices to share a common link. This is often used in the context of sharing a leased telephone line among three or more points. See also multidrop.
MVS Multiple Virtual System (also known as OS/VS Release 2). An IBM System 370 architecture operating system. MVS is available in several packages.
MVS/ESA. MVS/Extended System Architecture. The top of the MVS operating system line. The resource requirements of MVS/ESA dictate that it can only be used on top-of-the-line mainframes.
MVS/SP MVS/System Product. The low-end MVS operating system line, requiring the least amount of memory and storage.
MVS/XA MVS/extended architecture. The middle of the MVS operating system line, requiring more resources than MVS/SP, but less than MVS/ESA.
MVT Multiprogramming with a Variable Number of Tasks. An IBM System 360 architecture operating system.
NAK Negative acknowledgment. A transmission-control character transmitted by a receiver as a negative response to the sender. The normal response to a NAK is to retransmit the previous sequence.
Nanosecond One billionth of a second.
NAPLPS North American Presentation Level Protocol Syntax. An ANSI standard for the presentation of text and graphics.
NAS Network Application Support. A set of software products developed by DEC to integrate products on different systems. NAS is similar in concept to IBM's SAA.
NAU Network address unit. Any of the three addressable units in an IBM SNA network (in other words, SSCP, PU, and LU).
NCCF Network Communications Control Facility. An IBM NetView module that collects maintenance and status information from the SNA network. See also NetView.
NCP 1. Network Control Program. In IBM environments, the NCP is the software running in the communications controller to control the data communications environment. In DEC environments, the NCP is a utility that interfaces with lower-level network management modules. 2. In Novell environments, the Netware Control Protocol.
NCS Network Computing System. An architecture developed and promoted by Apollo (now HP) for implementing Remote Procedure Calls in a heterogeneous computer environment.
NETBIOS Network Basic Input Output System. A low level interface developed by IBM to allow PCs to share files and communicate with one another over a network. In brief, NETBIOS enables a PC program to open, close, read, write and lock network-based files. NETBIOS is often emulated by other network systems and forms the basis of Microsoft networking architectures.
NETdisk Part of Sun's Open Network Computing (ONC) architecture. NETdisk provides a network-based booting mechanism for diskless workstations. See also ONC.
Net-IPC See IPC.
NetView IBM's products and services that provide network management functions in an SNA network. Part of the greater SystemView systems management line, NetView is composed of a series of modules, including Network Communications Control Facility (NCCF), Network Problem Determination Application (NPDA), NetView Logical Data Manager (NLDM), NetView Management Productivity Facility (NMPF), and optionally NetView/PC. See also NCCF, NetView PC, NLDM, NMPF, and NPDA.
NetView/PC A PC-based product that enables non-SNA devices to participate in the Network Management Architecture offered by NetView. See also NetView.
NetWare The network operating system used in file servers in Novell networks.
Network Layer The third layer of the OSI Reference Model. Network Layer services find the best possible route for a message (or packet) to take through the network. See also OSI Reference Model.
Network Lock Manager Part of Sun's Open Network Computing (ONC) architecture. The Network Lock Manager provides record and file locking in conjunction with Sun's Network File System (NFS). See also NFS and ONC.
NeWS Network-extensible Windowing System. Sun's original Graphical User Interface (GUI) for the SunOS operating system. One unique aspect of NeWS is that it extended Adobe Systems' PostScript technology into the networking environment. And like many other Sun products, NeWS was licensed to other companies who ported the interface to other operating systems and environments. Sun has since moved on to use the Open Look GUI it co-developed with AT&T. See also GUI and Open Look.
NewWave HP's architecture for a Graphical User Interface (GUI) that provides a common multiwindowed, graphical environment from which the end user can access applications residing on other systems. See also GUI.
NFAR Network File Access Routines. DEC routines that can be used by programmers to integrate DECnet file access into their programs.
NFS Network File System. A specification created by Sun Microsystems for a network-based file server that allows for record-level and file-level access in a LAN environment.
NFT Network File Transfer. A DEC utility for file transfer via DECnet. Files can also be transferred from one system to another via the standard COPY command.
NIDL Network Interface Definition Compiler. Part of HP/Apollo's Network Computing System (NCS) architecture. NIDL enables each participating program to declare the formats and types of data it will be sharing through NCS. See also NCS.
NIS. Network Information Services. A module within Sun's Open Network Computer (ONC) architecture that maintains a common list of files in the NFS and who can access what files. Formerly called YP. See also ONC and NFS.
NJE Network job entry. NJE provides a mechanism to distribute the processing of a job (or jobs) among multiple hosts.
NLDM NetView Logical Data Manager. An IBM NetView module that monitors the information being collected from the network and looks for and reports any failures. See also NetView.
NMA Network management architecture. A general term used to refer to a vendor's or product's approach to managing a network.
NMP Network Management Protocol. A low-level protocol developed by AT&T that collects network failures and status data. See also Accumaster Integrator and UNMA.
NMPF NetView Management Productivity Facility. An IBM NetView module that provides online assistance to the personnel monitoring the network. See also NetView.
node An element of a LAN that has full routing capability. See also end node.
NonStop A Tandem Computers product line based on fault tolerance.
NPDA Network Problem Determination Application. An IBM NetView module that presents the current status of the network. See also NetView.
NRJE/3000 An HP 3000-based software product that provides SNA RJE access to an IBM mainframe using SNA SDLC communications. Also known as SNA NRJE and NRJE.
NRZ Non-return to zero. A line transmission scheme whereby multiple contiguous 1 bits are sent as opposing pulses, instead of two pulses with similar amplitude separated by a return to the zero (base) line. NRZ is frequently used by IBM equipment and infrequently used by other vendor's equipment.
NS/1000 and NS/3000 HP 1000 and HP 3000-based products that provide networking services in the HP AdvanceNet network.
ODA Office Document Architecture. An OSI upper-layer service that defines the format for complex documents containing text, data, graphics, voice, and video. Defined in ISO standard 8613.
OEM Original equipment manufacturer. The term OEM is used to describe companies that use equipment manufactured by another company as part of their product or solution. In most cases, the identity of the original manufacturer is concealed from the end user of the product. See also VAR.
OfficeVision IBM's integration of office automation and electronic mail products with the PC and PS/2 environment. OfficeVision can link PCs and PS/2s with AS/400 Office or PROFS. See also AS/400 Office and PROFS.
OLTP Online transaction processing. An approach to application processing that breaks up the various interactions between a user and application and enables them to be processed in small parts (transactions). Transaction processing environments have specific routing requirements, and the programs processing the transactions must be multithreaded.
ONC Open Network Computing. Sun's architecture for the interconnection of its computers and computer-related devices. This is equivalent to IBM's SNA, DEC's DNA, and HP's AdvanceNet.
Open Look AT&T's graphical user interface (GUI) for UNIX, developed jointly with Sun Microsystems. Open Look provides the user with a graphics-oriented, multiwindowed interface. See also GUI.
Oracle A relational data base product available on multiple computer systems developed and marketed by Oracle Corporation.
ORB Object Request Broker. A type of middleware that facilitates interoperability, and establishes a single platform on which objects request data and services on the client side or provides them from the server side.
OS/2 Operating System/2. A multitasking operating system for IBM-compatible computers that includes a graphical user interface called the Presentation Manager. OS/2 was originally developed jointly by Microsoft and IBM. Development is now solely the responsibility of IBM.
OS/SVS Operating System/Single Virtual Storage. An IBM System/370 architecture operating system. Also known as OS/VS2 Release 1.
OS/VS1 Operation System/Virtual Storage 1. An IBM System/370 architecture operating system.
OS/VS2 Operating System/Virtual Storage 2. See OS/SVS for OS/VS2 Release 1, MVS for OS/VS2 Release 2.
OSF Open Software Foundation. A group of computer-related companies that came together to define an industrywide standard for UNIX that is separate and distinct from AT&T's standard.
OSF/Motif The graphical user interface (GUI) released by the Open Software Foundation for its version of UNIX. See also GUI.
OSI Reference Model Open Systems Interconnection Reference Model. A layered architecture for the design and implementation of standards that relate to the interconnection of computer systems. The OSI Model is carved into seven layers. These seven layers, from top to bottom, are:
PA Precision Architecture. HP's name for its RISC architecture.
packet A group of binary digits--including data, origination and destination information--that is switched as a whole. See also frame.
Packet switching A networking technique in which multiple devices convert information into smaller packets and then send them on a common network. Within the network, packets can be routed or rerouted through many different nodes, as seen fit by the network. Packet-switching networks can be more cost effective than leased or dialable networks because charges are typically based on the volume of data instead of connect time or distance.
PAD Packet assembly/disassembly. A device that converts between the X.25 packet protocol (normally LAP-B) and a nonpacket protocol (such as those used by asynchronous terminals) so that nonpacket devices can use a packet network. In addition to the protocol conversion, the PAD takes large blocks of information from the local device and breaks them into smaller packets for the network. Conversely, the PAD also takes the small packets from the network and assembles them into a large block of information for the local device.
PAM Personal Applications Menu. An HP software program implemented in HP PCs in place of the standard COMMAND.COM program that comes with MS-DOS. PAM provides menu-driven services instead of COMMAND.COM's command line interpretation.
parallel A data transmission method in which the bits in a character are sent at the same time on 8 channels rather than on a single channel. See also serial.
parity The addition on a noninformation bit to a byte, making the number of ones in a byte either always odd or always even. This permits the detection of errors in bytes that have single-bit errors.
Pathworks A collection of products that enables PCs, PS/2s and Macintosh computers to participate in a DECnet network. This includes storing files, sharing printers and emulating terminals.
PBX Private branch exchange. A privately owned telephone routing system.
PC Personal computer. Originally a term used to refer to the IBM Personal Computer based on the Intel 8088 processor as introduced in 1981. The term PC has, however, gone on to refer to a larger class of machines that run MS-DOS (or PC-DOS) and provide some degree of hardware compatibility with the IBM PC.
PC/AT Personal Computer/Advanced Technology. IBM's first release of a Personal Computer using the Intel 80286 processor. The bus architecture of the PC/AT (two 8-bit PC-style slots and six 16-bit slots) went on to become popular in both 80286 and 80386 machines.
PC Convertible IBM's early attempt at an laptop computer based on the Intel 8088 processor running the MS-DOS (PC-DOS) operating system.
PC-DOS IBM's implementation of MS-DOS. See also MS-DOS.
PCjr IBM's home computer based on its original PC design. The PCjr featured limited memory and expansion capabilities.
PCL Printer Command Language. HP's generalized interface for its line of laser, ink-jet and dot-matrix printers. PCL uses scalable fonts and raster graphics but is not implemented in a high-level language. See also raster graphics.
PC LAN IBM's PC networking product.
PCM Plug compatible mainframe. Full-scale computer systems manufactured by companies other than IBM (such as Amdahl and Hitachi) that run IBM operating systems (for example, VM, and MVS).
PC-NFS PC Network File System. Part of Sun's Open Network Computing (ONC) architecture. PC-NFS allows for PCs and PS/2s to access information stored in the Network File System (NFS). PC-NFS also includes TCP/IP functions for terminal access and file transfer. See also ONC.
PC-NFS Lifeline Backup An add-on to Sun's PC-NFS product. PC-NFS Lifeline Backup permits multiple PC disks on the network to be backed up to a single network disk or tape. See also PC-NFS.
PC-NFS Lifeline Mail An add-on to Sun's PC-NFS product. PC-NFS Lifeline Mail permits a PC or PS/2 to participate in TCP/IP and UNIX electronic mail. See also PC-NFS.
PC-NFS Programmers Toolkit An add-on to Sun's PC-NFS product. It implements Sun's RPC and XDR in the networked PC environment. See also PC-NFS.
PC-RT Personal Computer Reduced instruction set Technique. See RT System.
PCSA Personal Computer Systems Architecture, now called Pathworks. See Pathworks.
PC/XT Personal Computer Extended Technology. The follow-up to the original PC (PC/AT), also based on the Intel 8088 processor.
PC/XT 286 A follow-up product to both the PC/XT and PC/AT that combined attributes of both machines into one system. The PC/XT 286 experienced limited success.
PDL Page Description Language. The general term for a software-based printer interface that defines the page layout and contents. Examples of PDLs include GPI, PCL, and PostScript. See also GPI, PCL, and PostScript.
PDN Public data network. A telephone company that offers data services to the public. A public data network does not have to use packet switching. See also PSN.
PDP DEC's line of 16-bit technical computers. The PDP computers use DEC's Q-bus architecture and run several DEC operating systems.
Phases In DEC terminology, the various revision levels of DECnet are termed phases. Since its first release in 1976, DECnet has had five major phases:
Physical Layer The first (lowest) layer of the OSI Reference Model. The Physical Layer defines the physical interface for the network (for example, RS-232 for point-to-point networks, CCITT X.21 for interfacing to public data networks and 802.3/4/5 for LANs). See also OSI Reference Model.
physical unit See PU.
Pick An operating system developed by Pick Systems that features integrated multiuser and database support.
PIU Path information unit. The combination of the TH and BIU information from the IBM SNA data format. See also BLU.
pixel The smallest element of a screen display. Each pixel in a display can be manipulated in terms of color and intensity. In most cases, the higher the number of pixels, the higher the resolution of the display.
PM. Presentation Manager. The graphical user interface for OS/2. See also GUI.
PNCP Peripheral Node Control Point. A point in a PU 2.1 node that provides limited IBM SNA management functions to facilitate LU 6.2 peer-to-peer communications. The presence or absence of the PNCP facility differentiates between a PU 2.1 and PU 2 device.
Point-to-point A physical connection between only two terminals or computers.
polling A method by which a master device tracks the status of its attached devices. When the master device polls its attached devices, each device responds, indicating that it is present.
POP Post Office Protocol. An electronic mail protocol for UNIX systems developed by Berkeley Software Distribution.
POSIX Definition of an operating system easily ported from one computer to another. Developed by IEEE as standard 1003.
PostScript A print description language developed by Adobe Systems that provides multifont, high-resolution output. PostScript features scalable fonts and raster-based graphics. Because it is implemented as a high-level language, PostScript can be implemented on virtually any computer system. PostScript is also used for fonts and graphics displays (and called Display PostScript in that context). See also raster graphics.
POWER Priority Output Writers, Execution Processors and Input Readers. An IBM Job Entry Subsystem. POWER/VS is for the DOS/VS operating system, and VSE POWER is for the DOS/VSE operating system.
POWERserver An IBM line of servers for use in engineering workstation networks. The POWERservers use a RISC architecture and are part of the RS/6000 computer line. See also POWERstation and RS/6000.
POWERstation A line of IBM engineering workstations using a RISC architecture. The POWERstations are part of the RS/6000 computer line. See also POWERserver and RS/6000.
POWER/VS See POWER.
Presentation Layer The sixth layer of the OSI Reference Model. The Presentation Layer standards ensure that data is presented to each application in a format that can be understood. This includes ASCII/EBCDIC conversion, data compression/expansion and so forth. See also OSI Reference Model.
PRI Primary Rate Interface. The high-end interface in the Integrated Services Data Network (ISDN). The PRI offers 23 64-Kbps data/voice lines and a twenty-fourth 16 Kbps management line. See also BRI and ISDN.
PRISM Parallel Reduced Instruction Set Multiprocessing. HP/Apollo's term for its approach to the RISC-architecture Domain computer.
Professional 300 A DEC product that implemented the basic PDP-11 computer architecture in a desktop model.
PROFS Professional Office System. An IBM office automation and electronic mail product for the VM operating system (and therefore for IBM mainframes).
protocol A set of rules by which two or more devices agree on information and code structures required for successful and error-free communications.
PS/1 Personal System/1. IBM's home computer introduced in 1990 and based on an 80286 processor. The PS/1 is an entry level system that does not use either the ISA or MCA bus standards. See also ISA, MCA, and PS/2.
PS/2 IBM's replacement to its original line of PCs. Most models in the PS/2 line feature IBM's MCA bus architecture. See also MCA.
PSDN Packet-Switching Data Network. A data network offering packet-switching data services. See also PDN and PSN.
PSN Packet-switching network. Also packet-switching node. A packet-switching network routes small fragments of information (called packets) over a series of switched circuits. A packet-switching node is a device within the packet-switching network that can route a packet between several other packet-switching nodes. See also X.25.
PSPDN Packet-switching public data network. A public data network offering packet- switching data services. See also PDN and PSN.
PU Physical unit. In IBM terminology, a physical unit controls the attached links and resources (logical units) of a node. See also LU.
PU Type 1 (PU 1) Workstations (for example, 3270).
PU Type 2 (PU 2) Cluster controllers (for example, 3274) and mid-range processors (for example, System/3X).
PU Type 2.1 (PU 2.1) Mid-range processors (for example, System/3X) that contain a PCNP. See also PCNP.
PU Type 4 (PU 4) Communications controllers (for example, 3705).
PU Type 5 (PU 5) Hosts that contain a SSCP. See also SSCP.
PW2 Personal Workstation Squared (the power of two). The Unisys line of PCs derived from the Sperry line of PCs.
Q-Bus Internal and peripheral bus used in the DEC MicroVAX and PDP-11 Series computers.
RAID Redundant Array of Inexpensive Disks. A cluster of disks, viewed by the end user as a single device, that mirrors data to multiple drives. RAID provides fast throughput, fault tolerance, and error correction.
Rainbow DEC's original offering in the PC market. The Rainbow ran MS-DOS or CP/M, but was not hardware-compatible with the IBM PC.
RAM Random access memory. The high-speed but volatile memory used by computers of all sizes.
raster graphics A type of graphics handling in which the image is broken into a horizontal series of dots, with each line of dots called a raster. Using this approach, the higher the number of horizontal rows, the finer the resolution of the printed page. See also dpi.
RD Receive Data. A lead in the RS-232C interface, RD is used as the reception line for incoming information. In the full 25-pin RS-232C standard, RD is pin 3. In the abbreviated, 9-pin PC interface, RD is pin 2. See also RS-232C and TD.
ReGIS Remote Graphics Instruction Set. DEC's graphics interface to its VT family of graphics terminals.
RES Remote Entry Services. See JES.
REX Remote Execution. Part of Sun's Open Network Computing (ONC) architecture. Enables a user on one system to execute commands on another system. See also ONC.
RFI Radio frequency interference. Radio waves that can potentially interfere with the operation of electronic devices. The U.S. Federal Communications Commission (FCC) is responsible for regulating whether an electronic device (such as a computer) generates too much RFI or electromagnetic interference (EMI). See also EMI and FCC.
RH Request/Response Header. The part of the IBM SNA data format that defines the type of data in the RU. See also BLU.
RI Ring Indicator. A lead in the RS-232C interface, RI is used to tell the terminal or computer that the phone is ringing. Normally RI is used with dial-up modems, in which case the receiving device can decide whether it wants to answer the call or not. In the full 25-pin RS-232C standard, RI is pin 22. In the abbreviated, 9-pin PC interface, RI is pin 9. See also RS-232C.
ring topology A LAN topology that features a central ring on to which nodes are connected. See also bus topology, tree topology, and star topology.
RISC Reduced instruction set computer. An architecture for computers in which more functions are moved into software while relying on highly optimized hardware to obtain optimum efficiency. See also CISC.
RJE Remote job entry. The ability to submit jobs on a computer from an IBM RJE work-station (a combination of multiple devices, such as a card reader, card punch, printer and console) to a Job Entry Subsystem. RJE is often used as a general means for file transfer; in this situation, a computer emulates an RJE workstation when communicating with another computer running (or emulating) a Job Entry Subsystem (JES). See also JCL and JES.
RJE/1000 and RJE/3000 HP 1000- and HP 3000-based software products that provide RJE access to IBM mainframes using bisynchronous communications.
RLL Run length limited. A disk encoding technique that results in 26 sectors per cylinder. RLL uses the ST-506 interface and is often used in place of MFM encoding on PCs because it is a denser storage technique (although it does require drives that are certified for RLL encoding). See also ESDI, MFM, SCSI, and ST-506.
RMON 2 A standard for remote monitoring. RMON 2 provides the means to proactively monitor an enterprise network, using an agent or probe to gather statistics and monitor for pre-set threshold levels.
RMS Record Management Services. The part of DECnet that handles requests to access remote files. RMS interfaces with FAL via DAP. See also FAL and DAP.
ROM Read only memory. A type of memory that can be read from but not written to. In contrast to RAM, ROM is low-speed, nonvolatile memory.
RPC Remote procedure call. A set of routines that enables a program operating on one system to communicate with a program running on another system. This interaction might be for the simple purpose of program-to-program communications or can be used to implement a network-distributed application, whereby the individual tasks of the application are distributed across multiple systems and coordinated through RPCs. See also API, APPC, and IPC.
RPC API RPC Application Program Interface. Part of Sun's Open Network Computing (ONC) architecture. A high-level interface that programmers can use to implement ONC RPC. See also RPC and ONC.
RPCGEN RPC Generator. Part of Sun's Open Network Computing (ONC) architecture. A programming aid that automates parts of the RPC coding requirements. See also RPC and ONC.
RS-232C An EIA standard for computer/terminal interfaces that defines the electrical and mechanical characteristics for the interconnection of data terminal equipment to data communications equipment for use at signaling rates up to 20,000 bps. RS-232C is frequently associated with a 25-pin connector. Often in a PC environment, only the following 9 of the full 25 leads are used: Carrier Detect (CD), Receive Data (RD), Transmit Data (TD), Data Terminal Ready (DTR), Signal Ground (SG), Data Set Ready (DSR), Request To Send (RTS), Clear To Send (CTS), and Ring Indicator (RI). See also CD, RD, TD, DTR, SG, DSR, RTS, CTS, and RI.
RS-422 An EIA standard for computer/terminal interfaces that defines the electrical and mechanical characteristics for the interconnection of data terminal equipment to data communications equipment for use at signaling rates up to 20,000 bps. RS-422 is frequently associated with a 5-pin connector.
RS-449 An EIA standard for computer/terminal interface that defines the electrical and mechanical characteristics for the interconnection of data terminal equipment to data communications equipment for use at signaling rates up to 2,000,000 bps. RS-449 is frequently associated with 37-pin and 9-pin connectors.
RS/6000 RISC System/6000. Introduced in 1990, the RS/6000 is IBM's line of RISC-based engineering workstations and servers. The RS/6000 line includes the POWERstation engineering workstations and POWERserver network servers.
RSCS Remote Spooling Communications Subsystem. The IBM Job Entry Subsystem for the VM operating system. RSCS does not, however, support attachment to SNA devices.
RSTS DEC's time-sharing operating system for the PDP/11 Series computers. See also CTS-300, DSM-11, and RSX.
RSX (RSX-11, RSC-11M, RSX-11M-PLUS) DEC's real-time and/or priority-driven multitasking operating systems for the PDP/11 Series computers. See also CTS-300, DSM-11, and RSTS.
RT System One of IBM's early engineering workstations. The RT System, originally called the PC RT, was based on IBM-proprietary RISC processors and had little in common with the rest of the PC line.
RTAM Remote Telecommunications Access Method. An IBM mainframe subsystem that handles application access and routing within the network. See also BTAM, TCAM, and VTAM.
RTE Real Time Executive. HP's operating system for the HP 1000 series computer.
RTS Request To Send. A lead in the RS-232C interface. RTS is raised by one side of the link when it wishes to transmit. If the other side is ready to receive, it responds by raising the Clear To Send (CTS) line. After transmission has begun, the Carrier Detect (CD) line is also raised. In the full 25-pin RS-232C standard, RTS is pin 4. In the abbreviated, 9-pin PC interface, RTS is pin 7. See also CD, CTS, and RS-232C.
RTS Reliable Transfer Service. In an X.400 electronic mail network, RTS works in concert with Message Transfer Agents (MTAs) to ensure that the best possible route for a message is taken. See also MTA and X.400.
RU Response Unit. The informational (data) portion of the IBM SNA data format. See also BLU.
SAA Systems Applications Architecture. A set of routines and transport mechanisms developed by IBM to isolate the development of applications from the specifics of the systems on which they will operate. Under SAA, a program can be implemented on one type of IBM system and then easily moved to another type of IBM system. An SAA-compliant application uses three SAA-defined interfaces: the common user interface, the common programming interface and the common communications support. See also common user interface, common programming interface, and common communications support.
SATAN Security Administrator Tool for Analyzing Networks. A free program that is used to detect vulnerabilities in networks. See also Gabriel.
SCSI Small Computer Systems Interface. SCSI is an intelligent, bus-oriented interface that enables a computer to transfer data between a disk, tape or other computer. A SCSI subsystem can support up to seven devices and each of these devices can communicate directly with one another. Thus, under SCSI, a computer can request the disk to back up to tape, and the disk will transfer directly to the tape without any further interaction from the computer. SCSI has become popular as a hard disk interface that offers storage of 26 or 36 sectors per track. One final advantage to SCSI as a disk interface is that it handles the relocation of bad disk areas on its own. SCSI is used in both PCs and mid-range systems. See also ESDI, MFM, RLL, and ST-506.
SDLC Synchronous Data Link Control. A bit-oriented protocol developed by IBM for use in SNA networks; SDLC is the de facto replacement for IBM bisynchronous communications protocols. IBM submitted SDLC to various standards organizations, and it has been adopted as ADCCP, HDLC, and LAP-B.
SecureRPC A part of Sun's Open Networking Computing (ONC) architecture. SecureRPC provides additional security to Sun's implementation of RPC. See also ONC and RPC.
serial A data transmission method in which the bits in a character are sent one after the other over a single channel. See parallel.
Session Layer The fifth layer of the OSI Reference Model. The Session Layer defines services that manage the administrative functions associated with moving information between two systems, such as requesting a logical link, maintaining the link and then tearing it down when the transfer is complete. See also OSI Reference Model.
SG Signal ground. A lead in the RS-232C interface. Signal ground provides a common reference ground between both sides of the data communications link. In the full 25-pin RS-232C standard, SG is pin 7. In the abbreviated, 9-pin PC interface, SG is pin 5. See also RS-232C.
Sixel DEC's graphics interface for printers. Sixel uses the lower six bits of a byte to correspond to six vertical printer dots. (In contrast, most Epson printers use all eight bits to correspond to eight vertical printer dots). The advantage to sixel is that the characters generated by using only the lower six bits stay within the realm of normal, displayable ASCII characters. Thus with sixel, graphics data can be sent to the printer over virtually any type of data communications link.
SLIP Serial Line Internet Protocol. A point-to-point link that can be used in a TCP/IP network to connect two TCP/IP devices together over a standard serial line.
SMP Symmetric multiprocessing. A multiprocessor implementation of a computer wherein an application can be broken (decomposed) into smaller tasks that can be distributed across the multiple processors and run in parallel.
SMTP Simple Mail Transfer Protocol. SMTP provides basic electronic mail functions in a TCP/IP network.
SNA Systems Network Architecture. IBM's architecture for the interconnections of its computer and computer-related devices. This is equivalent to DEC's DNA, HP's AdvanceNet, and Sun's ONC.
SNADS SNA Distributions Services. A distribution service for IBM computers operating in an SNA environment that allows for the transfer of files, documents, and electronic mail. See also DDM and DIA.
SNMP Simple Network Management Protocol. A lower-level service that hunts through the network for failures. SNMP is often implemented within TCP/IP.
SPARC Scalable Processor Architecture. Sun Microsystems' implementation of a RISC architecture computer.
SPARCserver Sun Microsystems' line of file and network servers based on its SPARC design. The high end of the SPARCserver line pushes into the traditional mid-range market in terms of power and architecture.
SPARCstation Sun Microsystems' line of engineering workstations based on its SPARC design.
Spectrum The code name for the HP 3000 line of RISC computers.
SPX Sequenced Packet Exchange. A Novell protocol that runs on top of Novell's older IPX protocol. Unlike IPX, SPX provides guaranteed delivery of network messages. In the OSI model, SPX is a transport layer protocol.
SQL Structured Query Language. A standard that defines the language for extracting information from a database.
SSCP System Service Control Point. A point in a host that provides SNA management functions. The presence of an SSCP enables a device to become an SNA PU 5.
SSP System Support Program. The operating system for the IBM System/36.
ST-506 A disk interface commonly used in PCs. The ST-506 interface can use either MFM or RLL encoding. See also ESDI, MFM, RLL, and SCSI.
Star Cluster A device that interfaces multiple DEC VAX systems (via CI links) to an HSC. This enables multiple VAX systems to access one or more sets of disk drives maintained by one or more HSCs. See also CI, HSC, and VAXcluster.
Star topology A LAN topology that features a central hub to which nodes are connected. See also bus topology, tree topology, and ring topology.
StarLAN A LAN implementation developed by AT&T that uses 1-Mbps cables in a star topology. HP used the original StarLAN implementation, then upgraded it to a 10-Mbps operating speed and changed the name to StarLAN-10.
Status Monitor Part of Sun's Open Network Computing (ONC) architecture. The Status Monitor enables one system to determine whether another system has been restarted. See also ONC.
Sun Sun Microsystems. A manufacturer of engineering workstations and the architect of NFS, ONC and SPARC. See also NFS, ONC, and SPARC.
Sun-3 Sun Microsystems' line of engineering workstations based on the Motorola MC68000 line of processors.
Sun-4 Sun Microsystems' line of engineering workstations based on its SPARC design. The Sun-4 term has been discontinued in favor of the SPARCserver and SPARCstation terms.
Sun386i Sun Microsystems' line of engineering workstations based on the Intel 80386 line of processors.
SunLink Sun's line of products for multivendor connectivity.
SunOS Sun's operating system for its engineering workstations. SunOS is based on both AT&T and Berkeley versions of UNIX.
switched line The line connection made as a result of dialing via the phone system (as opposed to a permanent leased line).
synchronous A form of transmission in which the sender and receiver exchange timing information on separate channels to send a frame with no space or marking between characters. Because no start/stop bits are required, synchronous transmission is more efficient than asynchronous transmission for long messages. See also asynchronous.
System/3X A general term used to refer to the IBM System/34, System/36 and System/38 lines of mid-range computers.
System/360 An IBM mainframe first released in 1964. Because of the way it handled multiple tasks and managed large amounts (at that time) of disk storage, the System/360 paved the way for the mainframe definition of today.
System/370 The System/370 was first released in 1970 as the follow-up to the IBM System/360 mainframe. The most important improvement in the System/370 was the introduction of virtual storage management. The System/370 remains the underlying architecture used in today's IBM mainframe products.
System/390 A system released by IBM in 1990 as a follow-up to the IBM System/370 mainframe. The performance of the System/390 has been greatly enhanced over that of the System/370 through the use of fiber-optic links and high-speed channel communications.
Systempro Compaq Computer's mid-range computer offering featuring multiple Intel processors operating in conjunction with the Extended Industry Standard Architecture (EISA)bus.
T1 A standard definition for digital transmission in the Bell System T-carrier digital environment. T1 defines a path having 1.544 Mbps that can be broken into 24 channels of 64 Kbps service. Each of the individual channels is said to have a Digital Signal Level Zero (DS-0) rate and all 24 as a whole result in the Digital Signal Level One (DS1) rate. See also Fractional T1.
TCAM TeleCommunications Access Method. An IBM mainframe subsystem that handles application access and routing within the network. See also BTAM, RTAM, and VTAM.
TCP/IP Transmission Control Protocol/Internet Protocol. TCP/IP is a set of network services that provide interoperability between heterogeneous systems. The TCP portion is responsible for providing reliable and recoverable communications between two end points. The IP portions sets up the routing used by TCP to transmit. Joining TCP/IP are two other low-level services--User Datagram Protocol (UDP) and Internet Control Message Protocol (ICMP)-- that are responsible for program-to-program communications and error reporting, respectively. Above TCP/IP are service applications to provide file transfer (FTP), terminal access (TELNET) and electronic mail (SMTP). TCP/IP was developed by the Defense Advanced Research Projects Agency (DARPA) and is commonly used as a transport mechanism in governmental, engineering and educational environments. See also FTP, ICMP, SMTP, TELNET, and UDP.
TD Transmit Data. A lead in the RS-232C interface, TD is used to transmit information across the interface. In the full 25-pin RS- 232C standard, TD is pin 2. In the abbreviated, 9-pin PC interface, TD is pin 3. See also RS-232C and RD.
TELNET TELNET is a TCP/IP application that enables a user to log on to a remote TCP/IP system.
terminal server A product that connects terminals to a LAN, enabling the terminals to establish sessions on host nodes. See also DECserver, DTC, LAT, and TS8.
TH Transmission header. The part of the SNA data format that defines the origin and destination of the message. See also BLU.
ThickLAN An term used to define the standard baseband coaxial cable (10BASE5) used as the backbone in most IEEE 802.3 and Ethernet LANs.
ThinLAN An term used to define the thin coaxial cable (10BASE2) used to interface PCs and office equipment in a LAN environment. ThinLAN segments can be interfaced to a ThickLAN backbone (or segment).
ThinWire The DEC term corresponding to ThinLAN.
TN Terminal Node. An IBM SNA term.
Token-passing discipline A LAN discipline whereby a specific message, termed a token, is passed from device to device on the LAN. The device that possesses the token has the ability to transmit on the LAN and when the device is done transmitting, it releases the token to the next downstream device. Token passing and CSMA/CD are the two most prevalent LAN disciplines is use. See also CSMA/CD.
token-passing ring See IEEE 802.5.
transceiver The device that attaches nodes to a LAN. Digital's H4000 and H4005 are typical transceivers. Transceivers interface with transceiver cables that attach to the nodes. See also MAU and AUI.
transparent data Binary data transmitted with the recognition of control characters suppressed.
Transport Layer The fourth layer of the OSI Reference Model. The Transport Layer standards ensure that information gets delivered to the intended destination and that it is delivered free of errors. See also OSI Reference Model.
tree topology A LAN topology that features a linear backbone onto which nodes or other LAN segments are connected. The tree topology and bus topology are similar and, in fact, the two terms are often interchanged. See also bus topology, ring topology, and star topology.
TS8 Terminal Server 8-ports. An HP terminal server that enables terminals to access HP 9000 hosts over a LAN running TCP/IP.
TSO Time Sharing Option. An IBM product that enables different users to use a mainframe by sharing the total available CPU on a percentage of time basis.
TTY Teletype. Originally a specific keyboard/hardcopy device, the term TTY has gone on to become a general industry term describing a dumb terminal that is operated on a key-by-key or line-by-line basis.
TurboIMAGE HP's proprietary relational database product.
Twinax IBM's twinaxial cabling system for the 5250 family of workstations, as used with the IBM mid-range system line (for example, System/36, System/38, and AS/400). Twinaxial is similar to coaxial except, as the name implies, it uses two conducting cores. See also coaxial.
UA User Agent. A software package that interfaces between a user and the X.400 electronic mail network. See also X.400.
UDP User Datagram Protocol. UDP provides a means for two programs in a TCP/IP network to directly communicate with one another.
ULTRIX DEC's implementation of UNIX for the VAX computer. See also VAXELN and VMS.
Unibus An internal and peripheral bus used in Digital's VAX and PDP-11 Series computers.
Unisys The company resulting from the merger of Burroughs and Sperry.
UNIX A multiuser, multitasking operating system. UNIX was designed by AT&T (Bell Laboratories) to be a industrywide operating system that could be implemented on virtually any type of computer. In reality, however, several different vendors have implemented their own versions of UNIX with proprietary extensions that are largely incompatible with one another.
UNMA Unified Network Management Architecture. AT&T's multivendor network management product.
V.3 CCITT international alphabet #5.
V.4 CCITT definition of structure for V.3 transmission over phone networks.
V.21 A CCITT standard for 300-bps modem operation over switched phone circuits.
V.22 A CCITT standard for 1,200-bps modem operation over switched and leased phone circuits.
V.22bis CCITT standard for 2,400-bps modem operation over switched and leased phone lines.
V.24 A CCITT standard for the interchange circuits between DCE and DTE. The V.24 standard is compatible with the RS-232C standard. See also DCE, DTE, and RS-232C.
V.25 A CCITT standard for automatic calling or answering equipment on switched networks.
V.26bis A CCITT standard for 1,200/2,400-bps modem operation over switched phone circuits.
V.27bis A CCITT standard for 2,400/4,800-bps modem operation over leased phone circuits.
V.27ter A CCITT standard for 2,400/4,800-bps modem operation over switched phone circuits.
V.28 CCITT definition of electrical characteristics for unbalanced circuits.
V.29 A CCITT standard for 9,600-bps modem operation over point-to-point leased phone circuits.
V.32 A CCITT standard regulating transmission up to 19.2 Kbps (asynchronous) or 1.2 Kbps (synchronous) over switched or leased phone lines.
V.33 CCITT standard for 12,200- and 14,400-bps modem operation over leased phone lines.
V.35 A widely used interface standard for data connections at rates up to 48 Kbps, defined by the CCITT. Note that despite the specification, the V.35 interface is frequently used to accommodate rates up to and including 64 Kbps.
V.42 CCITT error detection and correction scheme for modems.
V.42bis CCITT data-compression method for use with V.42.
VAN Value added network. A private network (normally over a wide area) offered on a commercial basis. DEC, HP and IBM all offer connectivity via their own proprietary networks. In the case of these three manufacturers, this network services its own locations, thus giving their customers local connection to the network at various locations across the country.
VAR. Value-added reseller. A company or organization that takes a product from one company, combines it with its own product (or service) and then resells the result to the end user. See also OEM.
VAX Virtual Address eXtension. DEC's wide-ranging line of 32-bit mid-range and high-end processors. Capable of running either VMS or Ultrix, these systems are typically installed on a DECnet (Ethernet) network. The VAX line includes the 4000, 6000, 8000, and 9000 series of models.
VAXBI The bus architecture used in the high end of the DEC VAX product line.
VAXcluster A unique configuration of VAX systems that enable multiple VAX systems to share access to a large pool of disk storage. VAXclusters were implemented by DEC to provide systems with computing and storage capacity similar to that of IBM mainframes.
VAXELN A real-time operating system for VAX computers. See also Ultrix and VMS.
VAXmate A DEC 80286-based personal computer.
VAXstation DEC's line of engineering workstations based on their proprietary VAX processor architecture.
Vectra HP's line of Pentium-based PCs.
VINES Virtual Network Software. PC network software by Banyan Systems. VINES is somewhat unique in that it can be implemented on top of existing network standards, like TCP, SNA or XNS.
virtual terminal The capability to logically connect to one type of computer (or node) from a different computer (or node).
VLSI Very large-scale integration. An approach to printed circuit-board design that uses the smallest possible number of individual components (chips), but with each component responsible for a broad set of functions. See also LSI.
VM Virtual Machine. An IBM System/370-style operating system that can host other operating systems as resident processes.
VME A general-purpose bus architecture. Frequently used in engineering workstations (such a Sun's) that use the Motorola MC68000 processor series.
VMS Virtual Management System. A DEC operating system for VAX computers. See also VAXELN and Ultrix.
VS1 See OS/VS1.
VS2 See OS/VS2.
VSE Virtual Storage Extended. An IBM System/370-style operating system.
VSE/POWER See POWER.
V T50 An early DEC terminal type. The V T50 models (for example, V T52 and V T55) were not ANSI-compatible terminals. The V T50 family includes models that support both text and graphics.
V T100 DEC's follow-up to its V T50 family. The V T100 family (for example, V T101, V T102, V T125) included support for both V T50 operation and ANSI-compatible operation. The V T100 family includes models that support both text and graphics.
V T200 DEC's replacement family for the V T100. The V T200 family introduced the now familiar keyboard layout with separate cursor, editing and numeric keypads. The V T200 family includes models that support monochrome text (V T220), monochrome graphics, (V T240), and color graphics (V T241).
V T300 DEC's follow-up to their V T200 family. The V T300 includes performance and ergonomic improvements to the basic V T200 design. The V T300 family includes models that support monochrome text (V T320), monochrome graphics (V T330), and color graphics (V T340).
V T400 DEC's follow-up to the V T300 line. The V T400 features improved memory, screen fonts, and session capabilities.
V T1000 DEC's X Window terminal. The V T1000 includes graphics processors in support of the graphics-intensive X Window environment.
V TAM Virtual Telecommunications Access Method. An IBM mainframe subsystem that handles application access and routing within the network. See also BTAM, RTAM, and TCAM.
V TS Virtual terminal services. An OSI upper-layer service to define a common terminal format that might be shared between open systems. Defined as ISO standard 9040.
WAN Wide area network. A network composed of systems that are relatively far apart. A WAN can also encompass a series of LANs connected together over a wide area. See also MAN.
windows An approach to the user interface that offers multiple applications to a user, with each application occupying a relatively small space (window) on the screen. The user can then select applications by window and zoom into or out of them. See also GUI. Also, the name of the Microsoft product that affords users this type of interface.
WPS-Plus DEC's word processing software for VMS systems. Also used as an integral part of ALL-IN-1. See also ALL-IN-1.
X.1 CCITT definition of service classes in public data networks.
X.2 CCITT definition of services and facilities in public data networks.
X.3 CCITT definition of packet assembly/disassembly (PAD) facilities in a packet-switching network.
X3.4 ANSI standard for a 7-bit information interchange code.
X3.15 ANSI specifications for bit sequencing of the X3.4 code in serial data streams.
X3.16 ANSI specifications for character and parity structure in X.34 transmissions.
X3.28 ANSI standard for the use of communication control characters.
X3.41 ANSI specifications for code extensions using the 7-bit V3.4 interchange code.
X3.66 ANSI definition of the Advanced Data Communication Control Procedures (ADCCP). See also ADCCP.
X.4 CCITT structure of V.3 transmission over public networks.
X.20 CCITT specification for interfacing devices using asynchronous transmission.
X.20bis A CCITT standard for interfacing terminals (DTE) and computers (DCE) over public data networks using asynchronous V-series modems.
X.21 CCITT specification for interfacing devices using synchronous transmission.
X.21bis A CCITT standard for interfacing terminals (DTE) and computers (DCE) over public data networks using synchronous V-series modems.
X.25 A CCITT standard for interfacing terminals (DTE) and computers (DCE) over a packet switching public data network (PSPDN). Because of its association with packet-switching data networks, X.25 has become almost synonymous with the term packet-switching network.
X.28 CCITT standard for start/stop device access to a packet assembly/disassembly unit (PAD). See also PAD.
X.29 CCITT exchange procedures for a PAD and a packet-mode DTE (normally a computer). X.29 is commonly used to facilitate terminal access over an X.25 network. See also PAD.
X.75 CCITT specifications for control and transfer between packet networks.
X.400 A standard for implementing electronic mail on diverse computer systems. X.400 has provisions for the exchange of messages, files and video information.
X.500 A standard for implementing common directory services on heterogeneous computer systems.
XDR External Data Representation. Part of Sun's Open Network Computing (ONC) architecture. XDR provides a common format for data being exchanged among heterogeneous systems. See also ONC.
XENIX An operating system marketed by Santa Cruz Operation (SCO) and based primary on UNIX, but offering some compatibility with MS-DOS.
XMI DEC's bus architecture used in the top-end VAX 6000 and 9000 systems.
XMODEM A public domain protocol designed to enable microcomputers to transfer files over telephone lines via modems.
XNS Xerox Networking System. Xerox Corporation's networking services implemented over an Ethernet LAN.
XON/XOFF A simple pacing mechanism implemented between sending and receiving units. Under this mechanism, the sender transmits until the receiver sends an XOFF character, signaling the transmitter to pause. When the receiver is ready for more data, is sends an XON character and the transmitter resumes sending. The XON and XOFF characters are normally the DC1 and DC3 control characters, respectively.
X Terminal A graphics-based computer or terminal that supports the X Window protocol.
X Window A specification developed at the Massachusetts Institute of Technology for a common graphical interface and set of protocols. X Window employs multiple windows to enable a user to concurrently access applications running on different systems.
YP Yellow Pages. See NIS.
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