D D conditioning A type of conditioning that controls harmonic distortion and signal-to-noise ratio so that they reside within specified limits. D/A Digital to analog. D/A converter Digital to Analog Converter. Generic term for any device that changes digital (binary) pulses into continuous wave (analog) signals. DAA See data access arrangement. DAC Digital to Analog Converter. DACS See digital access and cross-connect system. daisy wheel A letter quality printer that uses a rotating wheel with spokes. daisychaining Movement of a signal on a bus from one device to another in serial fashion. DAM Direct Access Method. DAMA See demand assigned multiple access. damping The technique of avoiding wide fluctuations in signals and instruments by introducing a form of time delay to prevent overcorrection or oscillatory conditions. DAP Data Access Protocol (Digital Equipment). dark fiber The fiber optic cables absent the electronic components that transmit telecommunications traffic through such cables. DARPA Defense Advanced Research Projects Agency. DASD Direct Access Storage Device; usually refers to disk storage for mainframe computers. DASF Direct-Access Storage Facility. DASM Direct-Access Storage Media. DASS 1. Digital access signaling system. A public network standard developed by the United Kingdom telecommunications industry. 2. Direct Access Secondary Storage. Same as near-line: storage on pretty-fast storage devices (e.g., rewritable optical) that are less expensive than hard drives but faster than off-line devices. DAT Digital Audio Tape. data Any coded information, including that which is recorded, processed or output by a computer or other machine. data access arrangement (DAA) Data communications equipment furnished or approved by a common carrier that permits attachment of privately owned data terminal and communications equipment to the common carrier's network. data base Collection of data, which is structured and organized in a disciplined fashion to facilitate information retrieval. data base management system DBMS; it provides utilities for database administration, backup recovery, and other activities. data base server A server that stores specialized data in an organized, readily-accessible manner. data circuit A communications facility that allows information transmission in digital form. data circuit terminating equipment (DCE) The interfacing equipment required to connect data terminal equipment (DTE) to or from a transmission circuit or channel. With an RS-232-C connection, the modem is usually regarded as DCE, while the terminal or computer is DTE. In a X.25 connection, the network access and packet switching node is viewed as the DCE. data collection Bringing data from one or more points to a central point. data communications The processes, equipment, and/or facilities used to transport signals from one data processing device at one location to another data processing device at another location. data compression A technique that saves storage space by eliminating gaps, empty fields, redundancy, or unnecessary data, thus shortening the length of records or blocks. data concentrator Unit that allows a common transmission instrument to serve more data sources than there are currently available channels. data conversion Converting data from one format to another. data density The ratio of image to white space on a scanned page. Useful in estimating storage needs. data encryption standard (DES) Symmetric, single-key encryption algorithm approved by the U.S. National Bureau of Standards for encrypting and decrypting data. data exchange (DX) Data that is transmitted or recorded in a format. data frame A unit of information, represented as a page or two of data, including the margin around the frame. data header User-defined title for a data frame. data interface -- automatic answer Data terminal feature that answers an incoming call (electronic mail) automatically. data line interface (DLI) The point where a data line is connected to a telephone system. data line privacy A user-controlled feature that cancels activities such as an executive override, attendant override, or a busy verification that could insert tones on the station line while in use -- generally used for station lines with such devices as computer terminals and facsimile machines. data link Describes the communications connection which is used to transmit data from a source to a destination. Data Link Connection Identifiers (DLCI) An identifier for a link that consists of the terminal equipment identifier (TEI) and service access point identifier (SAPI). data link control (DLC) Characters that manage transmission by performing error checking functions such as connect, initiate, terminate. Data Link Layer The second level of the OSI seven layer model of data communications, it puts messages together and coordinates their flow. data PBX A switch that permits a user on an attached circuit to select, usually one at a time, from among other circuits for the purpose of establishing a through connection. Distinguished from a PBX in that only digital transmission and not analog is supported. data rate Speed at which data is transmitted, measured in bps. data restriction A feature that is similar to data line privacy except data restriction is permanently activated. data service unit (DSU) Provides conversion of user binary data signals into the bipolar format required for DDS and T1. data set 1. AT&T name for modem. 2. A collection of related data. data sink A device that can accept data signals from a transmission device. data terminal equipment (DTE) 1. The data source, data sink, or both. 2. Equipment that usually includes control logic, buffer, and one or more input or output devices or computers; can also contain error control, synchronization, and station identification capability. 3. Equipment that converts user information into data signals for transmission or vice versa. data terminal interface (DTI) The connection point between a data terminal and telephone system. data transfer facility (DTF) Provides bi-directional data transfer between an IBM MVS system in a System Network Architecture (SNA) environment and VAX/VMS systems in a DECnet network. data transfer rate Average number of bits, characters, or blocks transferred from a data server to a data link. data transmission The sending of data from one location to another by means of signals over a channel. data transparency A PBX system that provides completely transparent data paths between connected terminals; signals can be transmitted without changing their electrical characteristics or coding. data unit The smallest unit of a file that can be accessed, transferred, etc. DATABUS Programming language (Datapoint). datagram In a packet network, a completely self-contained unit of data that is routed as an independent unit and bears no relationship to preceding or following units. DATANET Data network. dataphone A trade- and service-mark of AT&T. As a trademark, identifies data sets or modems supplied by AT&T for transmitting data over the regular telephone network; as a service mark, identifies the transmission itself. Dataphone Digital Service (DDS) An AT&T communications service in which data is transmitted in digital rather than analog form, thus eliminating the need for modems. DATASHARE Time-sharing system (Datapoint). Datel British Telecom's data transmission facilities. DB See decibel. DB/DC systems Data base/data communications systems. DB2 Database 2 (IBM relational data base system). DBA Data Base Administrator. DBMS Data Base Management System. dBRNC TMDecibels above reference noise, C-message weighted. dBRNO TMDecibels above reference objective. DBS See direct broadcast satellite. DBTG Data Base Task Group; a task group of the Conference on DataSystem Languages (CODASYL) that formed to develop a standard data basemodel for processing with the COBOL programming language. DCA 1. Document Content Architecture (IBM). 2. Distributed Communications Architecture (Unisys). 3. Defense Communications Agency (replaced by Defense Information Systems Agency). DCE 1. Distributed Computing Environment; an integrated set of services that supports the development, use, and maintenance of distributed applications. 2. Data Conversion Equipment. 3. Digital Control Element. 4. Data Circuit-terminating Equipment DCS 1. Data Communications System (IBM). 2. Data Control System (Unisys). 3. See digital cross connect system. DCT See discrete cosine transform. DDB Distributed Data Base. DDC 1. Direct Digital Control. 2. See direct department calling. DDCMP See digital data communications message protocol. DDD See Direct-Distance Dialing. DDE Dynamic Data Exchange; a protocol in use by Microsoft's Window graphical interface program that enables users to dynamically link application programs together. DDI See direct digital interface... DDL 1. Data Definition Language; languages supplied by large DBMSs that are used to specify how data is to be stored and managed within the system. 2. Data Description Language DDM Distributed Data Manager. DDMA Disk Direct Memory Access. DDN Defense Data Network. DDS 1. Digital Data System. 2. Dataphone Digital Services (AT&T). de facto standards Various standards that exist in the computer industry, which are not necessarily sanctioned by the standards approval bodies but have become popular implementations of vendor proprietary products. de jure standard A standard which has gone through the accreditation process by an official governing body, such as ANSI or CCITT. de-migration The most common way to cache from optical storage is to prefetch images from an optical server and move them to magnetic media, either on a file server or at the workstation, before they are requested by the user. Some vendors call this "demigration" (migration is moving data to optical storage). dead sector In facsimile, the elapsed time between the end of scanning of one line and the start of scanning of the following line. debugger A tool that is used to find problems, such as bad logic, in a computer program. The debugger allows users to view the action of the program on the computer and to step through the program in a variety of ways. DECconnect Digital Equipment's connectivity system for local area networks. It includes structured cabling and 802.3/Ethernet- based active components. decentralized processing An environment in which one or more networked nodes assume responsibility for processing applications and performing data processing functions. decibel (dB) A unit for measuring the relative strength of a signal parameter such as power or voltage. decimation A mismatch between capture resolution, typically 200 or 300 dpi for documents, and display resolution, typically 72 dpi on VGA monitors or 100 dpi on higher-end monitors. To display images, every third or fourth pixel is dropped out, or decimated. The result is a breaking experience that is hard to read. decision point A crossroads in a workflow system, where some parameter, either automatic or manual, has to take place before the document or object can move to the next task. DECnet Digital Equipment's proprietary network architecture and protocols that support communications over a variety of local and wide area network media. decoder (DEC) A device that has a number of input lines of which any number can carry signals, and a number of output lines but only one can carry a signal. decolumnization The process of reformatting multi-column scanned-in documents into a signal column. DECUS Digital Equipment Computer Users Society. DECwindows Digital Equipment's standard windowing environment, which is built on a foundation of standards, including the X Window System and XUI user interface. Supporting distributed computing, DECwindows applications can be accessed from anywhere on the network, no matter where the application resides. dedicated attendant link An intercom link is always available for use by the attendant to announce incoming calls. dedicated circuit A circuit leased from a common carrier by an end user that is used exclusively by that end user and is always available. dedicated lines Private circuits between two or more stations, switches, or subscribers. definition An expression of merit for image quality; has no formal measurement. delay The time interval between the time when a signal is sent to the time it is received. delay announcements Pre-recorded messages to incoming callers stating that they are being delayed and placed in an automatic call distributor (ACD) queue. delay dial A dialing configuration in which local dial equipment waits until receiving the entire telephone number before seizing a circuit to transmit the call. delay distortion Change in signal from the transmitting end to the receiving end resulting from the non-uniform speed of transmission of various frequency components of a signal through a transmission medium. delayed ringing A second set on a line receives the ringing signal after the first set has not responded within a preset number of rings. delimiter The character that marks the boundary between fields or the end of a record in a software program. Delphi A service that provides, for a fee, Internet hookups to individuals or companies. delta modulation (DM) A signal-difference sampling technique that uses a one-bit if the amplitude difference between two samples is increasing and a zero-bit if it is decreasing. deluxe queuing A mostly AT&T term describing a feature that permits incoming calls to be placed in a queue when all lines are busy. The queue can be either a Ringback Queue (RBQ) in which the user hangs up and is called back when a trunk becomes available, or an Off Hook Queue (OHQ) in which the user waits off-hook and is connected to the next available trunk. demand assigned multiple access (DAMA) Channel sharing by assigning capacity on demand to an idle channel or an unused time slot. demarc The demarcation point between the wiring that comes in from the local telephone company, and customer-premises equipment or CPE. Examples are RJ-11C, RJ-14C, or RJ-21X jacks, or a 66-block. demodulation The process of retrieving a signal from a modulated carrier wave. See also modulation. densitometer Instrument that measures the density of printed images; often used to check uniformity of color in a press run. density 1. Degree of darkness of an image. 2. Percent of screen used in an image. 3. The number of bits (or bytes) in a defined length on a magnetic medium. departmental imaging system A multi-workstation imaging system, typically used by at least three and usually by more than 25 people in a workgroup or department. See desktop imaging system. depth of field The range of distances away from the scanner within which the image stays in focus. derivation equipment Generates narrow band facilities from a wider band facility. DES See data encryption standard. desktop imaging system An imaging system with a single workstation - often a microcomputer - meant to be used by only one person at a time. desktop management interface (DMI) The name given to the set of application programming interfaces (APIS). desktop management task force (DMTF) A group of vendors formed to develop a strategy for managing networked desktop systems. destination field Field in a message header that contains the network address of the person to whom the message is sent. DFSMS Data Facility Storage Management Subsystem (IBM). DG/OCA Data General/OSI Communication Architecture. DHCP See Dynamic host configuration protocol. DIA 1. Digital Input Adapter. 2. Direct Interface Adapter. 3. Document Interchange Architecture (IBM). 4. Display Industry Association; an association of hardware and software industry companies whose purpose is to promote hardware and software standards for display terminals and related technologies. diagnostic function test (DFT) A program to test overall system reliability. diagnostic programs Computer programs used to check equipment malfunctions and to pinpoint faulty components. dial 1. A device that transmits a coded signal to actuate the central office switching equipment according to the digit dialed. A dial can be either a rotary device that is wound up and released to transmit open pulses (DC space pulses) or a touch-tone push-button device (dual-tone multifrequency {DTMF} signals). 2. Operating a dial or a keyset to transmit address information to automatic switching equipment. dial access to attendant Station user dials an operator call code to reach the attendant. dial level The selection of stations or services associated with a PBX using a one- or four-digit code (e.g., dialing 9 for access to an outside dial tone). dial tone (DT) An audible signal sent from an automatic switching system to a subscriber or user to indicate that the equipment is ready to receive dial signals. dial, dual-tone multifrequency (DTMF) A push-button device with 10 or more nonblocking push buttons designated 0 through 9. Each button, when operated, generates a double-frequency signal distinctive to that button. dial, rotary A type of calling device that generates pulses by manual rotation and release of a dial, the number of pulses being determined by how far the dial is rotated before being released. dial-pulse A current interruption in the DC loop of a calling telephone produced by the breaking and making of contacts when a digit is dialed. dial-repeating tie line/dial-repeating tie trunk A tie line arrangement which permits direct trunk to trunk connections without use of the attendant. dial-up Access to a switched network, usually through a dial or push-button telephone. dial-up line Telephone line that is part of the switched nationwide telephone system. dialed number identification service (DNIS) Equipment that recognizes the telephone number of the outbound call being made. dibit A group of two bits. In four-phase modulation, each possible dibit is encoded as one of four unique carrier phase shifts. The four possible states for a dibit are 00, 01, 10, 11. DIBOL Digital Business-Oriented Language; widely used in the commercial or business industry (Digital Equipment). DIBS Digital Integrated Business Systems (Digital Equipment). DICAM Datasystem Interactive Communications Access Method (Digital Equipment). DID See direct-inward dialing. DIF Data Interchange Format; used in many popular spreadsheet and DBMS software programs for PCs. digital Reference to the use of a discrete, dual-state format for representing information to be transmitted, stored, or processed. This binary format can consist of 0-1, on-off, true-false, or open- closed. With digital technology, sound is converted into electronic bits, as opposed to waves in analog service. digital absorption Digital signal loss due to absorption by the medium of transfer; similar to signal attenuation in analog transmission. digital access and cross-connect system (DACS) Digital switching system for routing T1 lines, and DS-O portions of lines, among multiple T1 ports. Connections are typically established in advance of the call, not together with the call as is the usual procedure. digital camera Video cameras that transform visual information into pixels, which can then be manipulated pixel by pixel. This information can also be compressed, stored and transmitted in a similar manner as traditional digital data. digital cellular The standard for equipment used for cellular telephone transmissions. digital cross-connect system (DCS) A specialized type of high-speed data channel switch which will switch transmission paths in response to dialing instructions. digital data communications message protocol (DDCM A uniform discipline for transmission of data between stations in a point-to- point or multipoint data communications system, with parallel, serial synchronous, or serial asynchronous data transfer. digital data service (DDS) A synchronized data-communications network formed by inter-connecting digital transmission facilities. digital loopback A diagnostic feature providing for a loopback of a digital signal from the remote modem, to provide a complete test of the line and remote modem. digital monitor A video monitor that accepts a digital signal from the computer and converts it into analog signals to illuminate the screen. Digital Network Architecture (DNA) Digital Equipment Corporation's network architecture. digital satellite system (DSS) A satellite system developed by Thomson Consumer Electronics and News DataCom. DSS can be used to receive DIRECTV and USSB programming, but it requires its own dish and decoding equipment which cannot be used to receive other satellite transmissions. digital signal A discrete or discontinuous signal; one whose various states are discrete intervals apart. See also analog transmission. digital simultaneous voice and data (DSVD) Allows personal computer users to share collaborative applications and voice conversation simultaneously over a single standard telephone line using a V.34/V.FC modem. digital speech interpolation (DSI) A kind of multiplexing where bandwidths are shared among a larger number of users for which there are circuits available. Silent periods of speech (50 percent of a conversation) are allocated to active users. digital switching A process in which connections are established by operations on digital signals without converting them to analog signals. digital termination system (DTS) An FCC-proposed system that integrates cellular radio for local access and microwave/satellite for long distance. digital transmission A transmission in which signal elements are in the form of discrete pulses of constant rather than variable (analog) amplitude. digitize To convert an image or signal into binary code. dime converter See converter, dime. DIMS Document Image Management System. DIO Direct Input/Output. DIP switch Dual In-Line Package. Tiny, on/off switches, usually mounted on a circuit board that configure the board in a semi-permanent way. DIR Document Information Retrieval. direct broadcast satellite A service that permits North American consumers to receive all digital video entertainment via satellite. direct department calling (DDC) Inward calls on a specific trunk or group of trunks are routed to certain stations or group of stations. direct digital interface (DDI) Trunks can be connected directly to T1 carriers. direct distance dialing (DDD) Automatically establishes toll calls in response to signals from the calling device of the originating customer without telephone company operator intervention. direct memory access (DMA) The ability of an external I/O device to act on and transfer data to and from memory without intermediary devices or circuits. direct station selection/busy lamp field (DSS/BLF) An operator console that enables the attendant to track the status of and connect directly with all stations in the system. direct trunk access Ability of a station with the appropriate class of service designation to directly access a specific trunk group. direct trunk group selection Allows the user or attendant to gain entry to a particular outgoing trunk instead of one chosen by the PBX out of group trunks. direct-in system access (DISA) See remote access. direct-in termination Incoming calls on a PBX may be programmed to route directly to the station without attendant intervention. direct-inward dialing (DID) A PBX feature permitting outside calls to be dialed and connected directly to the stations. direct-outward dialing (DOD) A feature that allows station users to dial a special access digit or digits to obtain an outside central office dialing capability without operator assistance in call completion. directed call pickup See call pickup. directory system PBX capability to store in memory a directory of all extensions and their corresponding user names; individual stations have access to this directory. DIS 1. Draft International Standard. 2. Data Interpretation System. DISA 1.Defense Information Systems Agency. 2. See direct-in system access. disconnect signal The on-hook signal by which the calling and called stations notify the switching equipment that an established connection is no longer needed and should be released. See also clear forward/clear-back signal. discrete cosine transform An audio coding algorithm. discriminating ringing See distinctive ringing. disk (file) server A mass storage device that can be accessed by several computers, usually through a local area network (LAN). disk array Combining redundant disk drives for more capacity, or for disaster recovery. See RAID. disk cache A place in memory where frequently recalled data is stored; enables speedier retrievals. disk controller A hardware device that controls how data is written to and retrieved from the disk drive. disk drive A device containing motors, electronics, and other gadgetry for storing (writing) and retrieving (reading) data on a disk. A hard disk drive is one which is generally not removable from the machine. A floppy disk drive accepts removable disk cartridges. disk duplexing A procedure that allows multiple disk drives to be installed with separate disk channels for each set of drives. Write operations are performed simultaneously because each disk drive uses a separate disk channel. disk management Refers to the control of information stored on a disk. The logical relationship of subdirectories to root directories, for instance. disk mirroring Data protection method in which a backup storage device maintains data identical to that which is stored on the primary device. If the primary device fails, the backup device can replace lost data. disk sector Magnetic disks are typically divided into tracks, each of which contains a number of sectors. A sector typically contains a predetermined amount of data, such as 256 bytes. display systems protocol (DSP) IBM protocol that permits 3270 BSL equipment to interface with PDN. distinctive dial tones To alert the user to the kind of call he or she is making, dial tones (internal or external) are varied. distinctive ringing Calls from different sources are distinguished by different ringing patterns. distortion The difference in value between the transmitted and received signals, typically refers to analog transmissions. distributed application A single system operating across the network to satisfy business and performance requirements, often with separated user interface, process modules, and data base components. distributed common control Systems that physically separate the various common equipment items which control the different modules of a switching system. distributed computing environment (DCE) A comprehensive integrated set of services that supports the development, use, and maintenance of distributed applications. LAP-B Link Access Procedure Balanced, CCITT-compatible protocol similar to LAP-D, provides error-controlled access to packet- switched networks. distributed data processing (DDP) A data processing arrangement that can save communications charges and improve network response times by transferring processing tasks to various host computers in multiple locations. distributed file server A system by which files residing on diskslocated throughout a network may be made available to workstations thatare also located throughout a network. distributed processing The use of intelligent or programmable terminals at sites remote from the user's main computer facility. distributed System Architecture (DSA) Bull HN Information Systems' network architecture. distributed Systems Network (DSN) Hewlett-Packard's network architecture. diverse access routing A telecommunications facility where the telecommunications signals are transported simultaneously over the same cable or over different cables in two different directions. If the cable is cut the traffic will continue without interruption to its destination. diversity To assure that a signal will reach its destination in microwave communications, two signals are sent and received at slightly different frequencies. divestiture Break-up of AT&T that mandated the company's reorganization of 22 Bell Operating Companies (BOCs) into seven regional holding companies (RBHCs). DLC Data Link Control; the set of rules used by two nodes on anetwork to perform an orderly exchange of information over the network. DLCI Data link connection identifiers. An identifier for a link that consists of the terminal equipment identifier (TEI) and service access point identifier (SAPI). DLE Data Link Escape character. DLI See data line interface. DLL Dynamic Link Library. DLP Data Link Processor (Unisys). DLS Data link switching, used for routing NetBIOS encapsulated in TCP/IP. DLSw Data link switching; a means of transmitting SNA and NetBIOS traffic over an IP network. DLT Digital Linear Tape. DLUR Dependent LU Requester. DLUS Dependent LU Server. DM See delta modulation. DMA See direct memory access. DME Distributed Management Environment; a set of integrated programs from the Open Software Foundation for systems and network management. DMI Digital Multiplexed Interface developed by AT&T. DML Data Manipulation Language (Digital Equipment). DMM Dynamic Memory Management. DMQ Direct Memory Queue. DMR Distributed Message Router. DMS 1. Data Management System. 2. Disk Monitor System (IBM). 3. Display Management System (IBM). 4. Distributed Maintenance Services (Bull HN). 5. Dynamic Mapping System (Hewlett-Packard). DMT 1. Direct Memory Transfer. 2. Discrete multitone; a technology that uses digital signal processors to transport more than six megabits per second of data, video, image and voice signals over existing one pair of copper wiring. DMTF See Desktop Management Task Force. DNA See Digital Network Architecture. DNIS See dialed number identification service. DNS See Domain Name System. do not disturb A feature allowing incoming calls to an extension to be routed to the attendant or a line that gives a reorder tone. DOA Digital Output Adapter. docket Critical information describing file transfer activity (e.g., who is communicating with whom, and why) that must be preserved intact if error recovery is to occur. document caching An intelligent way to speed up jukebox retrievals. Documents are staged in a local PC or in a network server based on three principles: (1) data is retrieved in more or less predictable ways; (2) no data access is truly random; and (3) the probability of re-access is higher than the probability of initial access. document management The capture, indexing, and intelligent retrieval of digitized (scanned) and electronic (wordprocessed) documents, as well as computer applications files (spreadsheets). document recognition The ability to capture all the information on a page (text and images) and recognize not only characters, but page structure (e.g., number of columns) and images and artwork. document retrieval The ability to search for, select, and display a document or its facsimile from storage. document staging In a document retrieval from an optical jukebox, the process where the image is fetched from the server by the software, and stored on the user's local PC until it is used. DOD 1.See direct-outward dialing. 2. drop on demand, a type of inkjet printer. Domain Name System Translates text-format computer names into their appropriate IP addresses. DOMSAT Domestic communications satellite. DOS Disk Operating System. DOS/VS Disk Operating System/Virtual Storage (IBM). DOS/VS-AF Disk Operating System/Virtual Storage-Advanced Functions (IBM). DOS/VSE Disk Operating System/Virtual Storage Extended (IBM). dot matrix Type of printer that produces text and graphics from many small dots arranged in a matrix. dot pitch The distance from the center of one phosphor dot in a CRT to the center of the nearest phosphor dot of the same color on the adjacent line. The smaller the distance, the sharper the monitor. Dot pitch is the major determinant in the clarity of an image on screen. double-sideband transmission (DSB) A variation of FM that increases the transmission rate by placing two carrier-wave-modulated frequencies at equal distance on either side of the carrier. downlink The satellite-to-earth transmission channel. download To transmit data from one computer into another computer. download Transferring file(s) from a remote host to a local computer. downloaded fonts Fonts that are sent to the printer either before or during the printing of documents. downsizing Converting systems that run on a large computer to a smaller computer. downward compatible When smaller or earlier models of a computer system can run the same software as larger or newer models. Also called backward compatible. DP 1.Dial-pulse (signaling). 2. distribution point. 3. Data Processing. DPCX Distributed Processing Control Executive (IBM). dpi Dots Per Inch; measures printer resolution. dpm Documents per minute. DPNSS A digital private network signaling system standard developed by British Telecom and other United Kingdom PBX suppliers. DPS 1. Disk Programming System (IBM). 2. Distributed Present Services (IBM). 3. Distributed Processing System (Bull HN). DPSK Differential phase-shift keying. A modulation technique in which the relative changes of a carrier signal phase are coded according to the data transmitted. DQDB Distributed queue dual bus. draft quality A lower quality, but faster, setting on some printers. Useful for quick reviews, before committing to LQ - Letter Quality. DRAM See dynamic random access memory. DRDA Distributed Relational Database Architecture; IBM's blueprint for allowing data to be distributed among DB2 and SQL/DS databases. driver or device driver A program routine that contains the machine codes necessary to control the operation of a peripheral device. Drivers typically include an operating system, but may also be bundled with application software. drop Portion of an outside telephone plant that extends from the telephone distribution cable to the subscriber's premises. DS-1C Digital Service, level 1C, is 3.152M bps in North America and is carried on a T1 facility. DS0 Digital Service, level 0, is 64K bps -- the worldwide standard speed for digitizing one voice conversation. DS1 Digital Service, level 1, is 1.544M bps in North America, 2.048M bps elsewhere. DS2 Digital Service, level 2, is 6.312M bps in North America and carried on a T2 facility. DS3 Equivalent of 28 T1 channels, communications access operating at 44.736M bps and carried on a T3 facility. DS4 Digital signal, level 4, is a 273M bps digital signal carried on a T4 facility. DSA 1. Direct Storage Access. 2. See Distributed Systems Architecture (Bull HN). 3. Digital Storage Architecture (Digital Equipment). DSB See double-sideband transmission. DSDD Double Sided, Dual Density (diskettes). DSE 1. Distributed Systems Environment (Bull HN). 2. Data Switching Equipment. DSI See digital speech interpolation. DSN See Distributed Systems Network. DSP 1.See display systems protocol. 2. Digital signal processing. Transforming an analog signal into digital and processing numerically. DSS 1. Decision Support System Single Density (diskettes). 2. See digital satellite system. DSS/BLF See direct station selection/busy lamp field. DSU See data service unit. DSVD Digital simultaneous voice and data. DSX Distributed System Executive (IBM). DTE See data terminal equipment. DTI See data terminal interface. DTMF See dial, dual-tone multifrequency, dual-tone multifrequency signaling. DTS See digital termination system. dual cable A type of broadband cable system in which separate cables are used for transmission and reception. dual-tone multifrequency (DTMF) signaling Sometimes called touch tone, a signaling method that uses specific pairs of frequencies within the voiceband for signals. One tone in each pair is chosen from a group of four low frequencies, and the other tone is selected from a group of four higher frequencies. The eight frequencies are 697, 770, 852, 941, 1209, 1336, 1477, and 1633 Hz. dual-tone multifrequency dial See dial. dumb bridges Bridges that must ascertain whether addresses are local or remote in order to correctly filter packets. dumb terminal A computer terminal that derives all its power from the computer to which it is attached. It has no programming or processing capabilities. DUP Disk Utility Program (IBM). duplex 1. A communications system or equipment that can carry information in both directions between two points simultaneously. (This term is also used to describe redundant equipment configurations, as in duplexed processors.) 2. The ability of a scanner to scan both sides of a sheet simultaneously. duplex circuit A circuit that is able to transmit data in both directions simultaneously (full-duplex). Half-duplex refers to transmission in only one direction at one time. duplex signaling (DX) A direct current signaling system that transmits signals directly on the cable pair. DXI Data exchange interface, a switched multi-megabit data service standard. dynamic allocation A technique in which the resources assigned for program execution are determined by criteria applied at the moment of need. Dynamic Data Exchange See DDE. dynamic host configuration protocol (DHCP) A protocol that permits clients to obtain their IP addresses dynamically from a master host. dynamic information In OCR, specific knowledge sources for the particular page or document - special characters, thesaurus words, etc. See static information. Dynamic Link Library See DDL. dynamic multiplexing A form of time-division multiplexing in which allocation of time is made according to the demands of the constituent channels. dynamic random access memory RAM that requires electronic refresh cycles every few milliseconds to preserve its data. dynamic routing A method in which a network router automatically reconfigures the routing table. dynamic scheduling In computerized communications systems, the decision concerning which program to execute next is made by the computer from moment to moment, depending on events taking place. In conventional batch applications, the computer has a fixed schedule. The schedule in a communications system changes dynamically with service and demand rates and event sequences. dynamic systems diagnosis A PBX system that allows system diagnostic programs to be run and selected through maintenance terminals.