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D
DA (data administration) — see DBA (database administration)
DA (data administrator) — see DBA (database administrator)
D/A (digital-to-analog)
The term used to describe a type of converter used to bridge digital and analog circuitry. D/A converters can either be stand-alone microcomponents, or included in the functionality embedded in advanced integrated circuits.
DAA (data access arrangement)
An interface device once used to interconnect customer-owned data terminal equipment (DTE) to a telephone network. This interface is now generally integrated into such equipment. See DTE.
DAC (digital-to-analog converter)
Component used to bridge the digital and analog circuitry contained in certain advanced integrated circuits. Also known as a "D/A converter."
DAC (Design Automation Conference)
Annual electronics industry conference devoted to electronic design automation (EDA) methodologies and tools. See EDA.
DAE (Disk Array Enclosure)
A type of disk array module offered in EMC's CLARiiON storage systems.
daemon
A program that runs in the background and provides system services on an ongoing, indefinite basis for one or more client applications, such as printing files on a shared printer.
daisy chain
The connection of multiple devices in a serial fashion. An advantage of daisy-chaining is savings in transmission facilities. A disadvantage is that if a device malfunctions, all of the devices daisy-chained behind it are disabled.
DAMA (demand assigned multiple access)
Allocation of communication satellite time to earth stations as the need arises.
DAO (Data Access Objects)
The programming interface for the Microsoft Jet database engine; a precursor to ActiveX Data Objects (see ADO).
DAP (Directory Access Protocol)
An X.500 protocol for client access to server directories. A less complex version DAP, Lightweight Directory Access Protocol (LDAP), has emerged as the as the favored method of interfacing among different directories, especially for Internet use. See X.500 and LDAP.
DAPP (data analysis and provider profiling)
A category of healthcare value-added applications that support analysis of administrative data for the purposes of network management, actuarial and underwriting functions, medical management, and performance measurement.
dark fiber
Fiber-optic cable deployments that are not yet being used to carry network traffic. (The word "dark" refers to the fact that no light is passing through the optical fibers.)
DARPA (Defense Advanced Research Projects Agency)
The U.S. Defense Department agency that developed the Advanced Research Projects Agency Network (ARPANET, the forerunner of today's Internet) and Transmission Control Protocol/Internet Protocol (TCP/IP). See Internet and TCP/IP.
DAS (direct-attached storage)
A broad category of storage technology that includes:
• Redundant array of independent disks (RAID) storage that is internal and host-attached (both the RAID controller and software technologies and the hard disk drives are housed within the server)
• Host-attached, external RAID storage (the RAID controller and software technologies are housed within the server, and the hard disk drives are housed separately from the server in a high-availability RAID enclosure)
• RAID controller-based storage (a separate enclosure — incorporating both the RAID controller and software technologies and the hard disk drives — is attached directly to the server).
See RAID.
DASD (direct-access storage device)
Generic nomenclature for a storage peripheral that can respond directly to random requests for information. The term usually denotes a disk drive.
DASS (Digital Access Signaling System)
The original British Telecom (BT) Integrated Services Distributed Network (ISDN) signaling system developed for single-line and multiline digital access to the public network, but used in the BT ISDN pilot service for single-line access only.
DASS2 (Digital Access Signaling System 2)
A message-based signaling system developed by BT and its suppliers for multiline integrated digital access to the public network; an updated version of Digital Access Signaling System (see DASS).
DAT (digital audiotape)
A magnetic tape that stores audio data in digital form.
data
Raw facts and figures that a computer processes into usable information. Data such as cash receipts mean little until processed into information such as an open receivable balance.
data access arrangement (see DAA)
Data Access Objects (see DAO)
data administration — see DBA (database administration)
data administrator — see DBA (database administrator)
data analysis and provider profiling (see DAPP)
data archive
A static, independent copy of a related set of files for intermediate or long-term storage, usually to satisfy financial-reporting, audit, regulatory and ad hoc retrieval requirements. The primary files can be left intact or deleted when the archive is created.
database
An electronic filing system organized by fields, records and files. A field is a single piece of information, a record is a set of fields and a file is a collection of records.
Database 2 (see DB2)
database administration/administrator (see DBA)
database management system (see DBMS)
database marketing
The process of analyzing database-captured customer, product and purchasing information in order to allocate marketing resources to those activities that have the greatest impact and return on profitable customer relationships.
database partitioning
The practice of separating a database into portions that may reside on more than one disk volume or more than one system.
data center
The department in an enterprise that houses and maintains back-end information technology (IT) systems and data stores — its mainframes, servers and databases. In the days of large, centralized IT operations, this department and all the systems resided in one physical place, hence the name "data center." With today's more distributed computing methods, single data center sites are still common, but are becoming less so. The term continues to be used to refer to the department that has responsibility for these systems, no matter how dispersed they are.
Datacenter Server (see DCS)
data circuit
A communications facility that enables transmission of data in either direction, in either analog or digital form.
data circuit-terminating equipment — see DCE (data communications equipment)
data communications
The transmission, reception and validation of data — specifically, the transfer of data over one or more communications links, using appropriate protocols, by means of an electromagnetic or optical transmission system.
data communications equipment (see DCE)
data compression
A technique that saves storage space or bandwidth consumption by eliminating gaps, empty fields, redundancies or unnecessary information to shorten the length of data records or blocks.
data control language (see DCL)
data conversion
The process of changing data from one form of representation to another.
data definition language (see DDL)
data dictionary
A repository of information about data that supplies the meaning of the data, its relationship to other data, its origin, its usage and its format. The dictionary assists management, database administrators, system analysts and application programmers in effectively planning, controlling and evaluating the collection, storage and use of data. A data dictionary manages data categories such as aliases, elements, records, structure, stores, models, flows, relationships, processes, functions, dynamics, size, resource consumption and other, user-defined data attributes.
Data Encryption Standard (see DES)
data exchange interface (see DXI)
Data Facility Storage Management Subsystem (see DFSMS)
datagram
A packet of data that can be transmitted over a packet-switched system in a connectionless mode. This is a type of "fire and forget" mechanism that has no concept of a transaction or acknowledgment.
data integrity
The assurance that data has not been lost or corrupted in the course of being stored or communicated. Aside from hackers or deliberate destruction, the main threats to data integrity include network transmission errors such as dropped packets, storage hardware errors such as bad disk sectors, and application errors such as database replication errors. Methods of ensuring data integrity include redundancy and parity checking for data storage and transmission, and two-phase commit and template filtering for data entry and database management.
Data Interchange Format (see DIF)
Data Language I (see DL/I)
data link
Any serial data communications transmission path, generally between two adjacent nodes or devices and without any intermediate switching nodes. See data link layer.
data link layer
The layer in the Open Systems Interconnection (OSI) model concerned with transmission of data between adjacent network nodes. It is the second layer in the OSI model, between Layer 1 (the physical layer) and Layer 3 (the network layer). See data link and OSI.
Data Link Switching (see DLSw)
data local-exchange carrier (see DLEC)
data logging
Recording data about events in the time sequence in which they occur.
data manipulation language (see DML)
data mart
A system that provides access to a limited number of data sources and a data model to aid in decision making for a specific business or application — in contrast to the enterprisewide, strategic focus of the data warehouse. See data warehouse.
data mining
The process of discovering meaningful correlations, patterns and trends by sifting through large amounts of data stored in repositories. Data mining employs pattern recognition technologies, as well as statistical and mathematical techniques.
Data-Over-Cable Service Interface Specification (see DOCSIS)
data PBX
A private branch exchange (PBX) devoted to data, rather than voice, communications. See PBX.
data processing
Rapid processing of large amounts of information through mechanical or electronic means — a function originally performed by tabulating machines, and today performed by computers.
data rate
The speed at which a channel carries data, typically measured in bits per second.
data service unit (see DSU)
data synchronization
A form of embedded middleware that allows applications to update data on two systems so that the data sets are identical. These services can run via a variety of different transports but typically require some application-specific knowledge of the context and notion of the data being synchronized.
data terminal equipment (see DTE)
Data Universal Numbering System (see DUNS)
data VPN
A virtual private network (VPN) devoted to data, rather than voice, communications. See VPN.
data warehouse
A storage architecture designed to hold data extracted from transaction systems, operational data stores (ODSs) and external sources. The warehouse then combines that data in an aggregate, summary form suitable for enterprisewide data analysis and reporting for predefined business needs. The five components of a data warehouse are:
• Production data sources
• Data extraction and conversion
• The data warehouse database management system (DBMS)
• Data warehouse administration
• Business intelligence tools
See DBMS, ODS and business intelligence.
dB (decibel)
The unit for measuring the relative strength of a signal, equal to 10 times the logarithm of the ratio of one signal's power to that of another — or to a reference level (typically one milliwatt, in electronics and radio).
DB (see database)
DB2 (Database 2)
IBM's relational database management system (RDBMS) offering, originally built for Multiple Virtual Storage (MVS) systems. It uses Structured Query Language (SQL) as its data manipulation and definition language. IBM has released versions of DB2 for several other operating systems, such as Windows and Unix. See RDBMS, MVS and SQL.
DBA (database administration)
The role of a database administrator, i.e., managing the data contained in a database. Also known as "data administration."
DBA (database administrator)
The person responsible for managing data, namely data set placement, database performance, and data recovery and integrity at a physical level. Also known as a "data administrator."
DBCS (double-byte character set)
A type of character set large enough to support languages with high numbers of characters (notably Asian languages such as Kanji).
DBM (see database marketing)
DBMS (database management system)
A system that enables end users or application programmers to share data. It provides a systematic method of creating, updating, retrieving and storing information in a database. DBMSs also typically perform data integrity, data access control, and automated rollback, restart and recovery functions. See database.
DBS (direct broadcast satellite)
A wireless technology for broadcasting by transmitting a compressed high-speed signal via satellite.
DC (direct current)
Type of power supply in which the electric current flows in only one direction, as distinguished from an alternating current (AC). See AC.
DCA (distributed component architecture)
An architecture in which the various logical functions of an integration broker (such as message capture, transformation, routing and delivery) are implemented as separate components that can be executed on different machines.
DCD (Document Content Description)
A World Wide Web Consortium specification for expressing Extensible Markup Language (XML) data types and value constraints. See XML.
DCE (data communications equipment)
Equipment (also known as "data circuit-terminating equipment") that performs the functions required to connect data terminal equipment (DTE) to a data circuit. In the Electronic Industry Alliance's RS-232 specification, designation as either DTE or DCE determines the signaling role in handshaking. See DTE and RS-232.
DCE (Distributed Computing Environment)
A vendor-neutral framework created by the Open Software Foundation (now The Open Group) to support distributed applications by integrating the appropriate technologies into a single environment while addressing interoperability, standards and security. DCE integrates remote procedure calls, presentation services, a naming directory, security, threads (sequential flows of control similar to tasks), time services (to synchronize clocks) and a distributed file system.
DCE (distributed computing environment)
Generic term for a computing environment in which data and applications are distributed among disparate computers or systems, but are connected and integrated such that they function as a single environment.
data control language
DCL (data control language)
Statements used to grant or revoke data access and update privileges in Structured Query Language (SQL). See SQL.
DCM (document component management)
A concept that applies the principles of managing entire documents to managing parts of documents. Every significant unit of information is identifiable as a separate entity and is subject to the same core library services (such as check in/check out, version control and security) that integrated document management (IDM) provides on complete documents or sections of documents. Structural markup within the document (for example, using XML) identifies the components of information. Unlike IDM, information about the content — metadata or attributes — is captured on the inside and embedded in the content rather than stored on the outside as a separate index of information. This is essential when pointing to information elements required for selective reuse, updating, associating data with related information, storing translations, validity checking and other component-level processes. See IDM.
DCOM (Distributed Component Object Model)
A version of Microsoft's Component Object Model (COM) that enables application components to be distributed over several computers through the use of a remote procedure call (RPC). See COM and RPC.
DCS (Datacenter Server)
A Microsoft product focused on the highest end of the Windows 2000 server market. It provides support for up to 32-way systems, as much as 64 gigabytes of physical memory, and four-node, high-availability clustering.
DCS-1800 (Digital Cellular Service 1800)
A GSM-based standard for digital cellular communications in the 1.8-GHz frequency range, introduced in Europe and Asia in the mid-1990s.
DCS (digital cross-connect system)
A computerized facility allowing 1.544-Mbps DS1 lines to be remapped electronically at the 64-Kbps DS0 level. This means that DS0 channels can be individually rerouted and reconfigured into different DS1 lines. See DSx series.
DCS (distributed control system)
A form of direct digital control for process automation, distributing specialty-purpose controllers across a common communication network throughout a manufacturing plant. In a DCS, measurement, control and communications are distributed in function and location. By partitioning and distributing control functions, local controllers throughout the plant remain in control of the process if central control room consoles are lost. Likewise, if one local control station fails, other local controllers continue to operate. DCSs are usually deployed in fault-tolerant modes using redundant system configurations to achieve high measures of system availability.
DCT (discrete cosine transform)
An algorithm used for video compression.
DDA (Distributed Data Architecture)
Groupe Bull's scheme for data interoperability.
DDBMS (distributed database management system)
A database management system (DBMS) that enables end users or application programmers to view a collection of physically separate databases as a logical single-system image. The concept that is most fundamental to the DDBMS is location transparency, meaning the user should not be conscious of the actual location of data. See DBMS.
DDD (direct distance dialing)
A telephone exchange service that enables telephone users to place long-distance calls without operator assistance.
DDE (Dynamic Data Exchange)
A Microsoft technology for sharing data between two applications or files. DDE enables data used in one file to be automatically updated in the other. Both applications must be in use, and DDE does not work over a network. Object Linking and Embedding (OLE) provides a more sophisticated approach. See OLE.
DDL (data definition language)
A language used to describe the data model for a Structured Query Language (SQL) database — that is, the names and access paths for the data and how they are interrelated. See SQL.
DDM (see distributed data management)
DDN (Digital Data Network)
A network service established in China in 1994, connecting Beijing, Tianjin, Shanghai and other provincial capitals. Each post and telecommunications administration in China has a department regulating DDN service in its region.
DDNS (Dynamic Domain Name System)
A technology that automatically updates the logical names of dynamically assigned Internet Protocol (IP) addresses in the Domain Name System (DNS) server of an IP network. Specifications for a standard approach to DDNS were defined in Request for Comment 2136, introduced in 1997. See IP and DNS.
DDS (digital data service)
A dedicated data transmission service that operates over interconnected digital private lines.
DDS (Digital Data Storage)
A format for digital tape storage, originally introduced in 1988 by Hewlett-Packard and Sony.
decibel (see dB)
decision support system (see DSS)
DECnet
A family of peer-to-peer, Ethernet-based network products from Compaq (formerly Digital Equipment), now part of Hewlett-Packard.
DECT (Digital Enhanced Cordless Telecommunications)
An interface specification for European digital mobile telephony. DECT employs 10 carrier frequencies between 1.88 gigahertz (GHz) and 1.9 GHz, and has a transmission speed of 144 kilobits per second. It is typically used for short-range communications and wireless-local-loop applications.
dedicated circuit
A communications line dedicated for private enterprise or personal use.
deep packet inspection (see DPI)
Defense Advanced Research Projects Agency (see DARPA)
degaussing
A technique used to permanently erase any trace of data from magnetic media and hard drives. When done properly, it renders any previously stored data unreadable. Degaussing requires the purchase of a degaussing product, frequent product testing and a skilled operator. Unfortunately, some degaussers will also damage the electronics on a hard drive, thereby permanently disabling the data and the device.
delay distortion
The change in a signal from the transmitting end to the receiving end, resulting from the tendency of some frequency components within a channel to take longer to be propagated than others.
delimiter
In data communications, a character that separates and organizes elements of data.
delta modulation
A method of representing a speech waveform (or other analog signal) in which successive bits represent increments of the waveform. The increment size is not necessarily constant.
demand assigned multiple access (see DAMA)
demand planning
The process of forecasting and managing the demand for products and services by end users, as well as by intermediate supply chain members.
demand management
The process of matching future demand with (sometimes constrained) projected available supply.
demilitarized zone (see DMZ)
demodulation
The process of retrieving data from a modulated carrier wave; the reverse of modulation.
DEN (Directory-Enabled Networks)
An initiative formed by Microsoft and Cisco to define a directory schema foundation for common network objects, and for the use of Lightweight Directory Access Protocol (LDAP) as a query protocol. Microsoft and Cisco turned over control of DEN to the Distributed Management Task Force, which has incorporated the specification under its Common Information Model (CIM). See LDAP and CIM.
denial of service (see DoS)
dense wave division multiplexing (see DWDM)
DES (Data Encryption Standard)
A security specification developed by IBM in 1977. Still in use today, it is available at no charge from many online bulletin boards and is based on a single-key encryption algorithm. If user A wants to send an encrypted file to user B, user A would first encrypt it with a secret key. User B would then decrypt the file using the same key. Recipients must prearrange for possession of the appropriate key for decryption to take place.
Design Automation Conference (see DAC)
design for logistics (see DFL)
design for manufacturability (see DFM)
desktop alternative
A computer system that meets all the criteria for a notebook PC but is designed to replicate the functionality of a desktop. It weighs 6 pounds or more. The screen can be as large as 16 inches, with Super Video Graphics Array (SVGA) resolution or higher. Target markets include engineers and other users who require certain desktop features and functions in a portable format.
Desktop Management Interface (see DMI)
desktop management services
The management and optimization of an enterprise's distributed desktop and associated network environment — as opposed to a stand-alone PC or workstation environment. Desktop management typically involves long-term contractual relationships — as opposed to finite projects — and involves the management of one or more IT functions in a customer's distributed desktop infrastructure. The primary focus of outsourced services is on operational aspects of a customer's distributed desktop environment. These services include, but are not limited to, the following:
• Consulting
• Design
• Procurement
• Integration
• Hardware and software maintenance
• Help desk management
• Asset management
Desktop Management Task Force (see DMTF)
desktop publishing
The process of designing and publishing documents using desktop software and hardware, such as PCs, printers and scanners. The desktop-publishing software category includes page layout and design applications from vendors such as Adobe Systems and Quark.
desktop services
Acquisition, maintenance and ongoing management of PC hardware and software assets.
desktop videoconferencing
The ability of two or more geographically separated users to meet via their personal computers. A typical system involves a PC, a monitor-mounted camera, a network connection, and special software that facilitates the exchange of video and audio.
Deutsches Institut fur Normung (see DIN)
device relationship management (see DRM)
DFL (design for logistics)
A product design approach that considers logistical issues, such the manner in which the product will be stored or transported.
DFM (design for manufacturability)
An approach for designing products in ways that optimize their manufacture.
Dfs (Distributed File System)
A Microsoft Windows 2000 feature that allows multiple servers to provide file shares under the hierarchy of a common logical share. Multiple servers can sponsor identical file shares to provide redundancy and differing levels of response time.
DFS (Distributed File System)
A Distributed Computing Environment (DCE) standard that provides users with a common file system across different operating systems. When a file is moved, DFS tracks the new location by storing its address in a database. DFS also eases backup difficulties by automating regular backup routines across each cell through a backup server. See DCE.
DFSMS (Data Facility Storage Management Subsystem)
The conceptual repackaging of IBM's Data Facility family of products and Resource Access Control Facility (RACF). It is intended to simplify the management and use of external storage resources by providing a device-independent means of requesting services by data set. See RACF.
DFSMSdfp (DFSMS Data Facility Product)
One of four components of IBM's Data Facility Storage Management Subsystem (DFSMS). DFSMSdfp provides data access and catalog management functions. See DFSMS.
DFSMSdss (DFSMS Data Set Services)
An IBM software product that provides copy, dump-restore and storage space management functions. It is one of the four modules of IBM's Data Facility Storage Management Subsystem (DFSMS). See DFSMS.
DFSMShsm (DFSMS Hierarchical Storage Manager)
The module of IBM's Data Facility Storage Management Subsystem (DFSMS) that provides automatic space and availability management within a storage hierarchy. See DFSMS.
DFSMSrmm (DFSMS Removable Media Manager)
The tape management module in IBM's Data Facility Storage Management Subsystem (DFSMS). DFSMSrmm is used to track the location of all tapes, including those at remote sites or in transit. See DFSMS.
DHCP (Dynamic Host Configuration Protocol)
An Internet Engineering Task Force (IETF) Transmission Control Protocol/Internet Protocol (TCP/IP) specification for allocating Internet Protocol (IP) addresses and other configuration information based on network adapter addresses. It enables address pooling and allocation and simplifies TCP/IP installation and administration. See IETF, IP and TCP/IP.
DHTML (Dynamic HTML)
Netscape and Microsoft technology that offers client-side mechanisms for enhancing the capabilities of Web browsers and Hypertext Markup Language (HTML) documents. DHTML is often confused with dynamically generated HTML, which is HTML is generated by a program or service. Dynamically generated HTML might contain DHTML, but the terms are no synonymous. See HTML.
diagnostic program
A software routine used to check equipment malfunctions and to pinpoint faulty components.
Dialed Number Identification Service (see DNIS)
dial-up
The process of, or the equipment or facilities involved in, establishing a temporary network connection via the public switched telephone network.
DICOM (Digital Imaging and Communications in Medicine)
A communication standard developed by the American College of Radiology and the National Electrical Manufacturers Association for use in digital radiology systems (such as computed-radiography, computed-tomography and magnetic resonance imaging systems).
DIF (Data Interchange Format)
A file format developed for VisiCalc, the first electronic spreadsheet. Still used today as a means for transferring files to and from spreadsheets.
DIF (Directory Interoperability Forum)
Coalition formed in 1999 by IBM, Novell, Oracle, Lotus Development and Isocor to promote the use of Lightweight Directory Access Protocol (LDAP) by developers, and to accelerate directory interoperability standards. See LDAP.
Diffie-Hellman
The first widely deployed public-key algorithm. Initially owned by Cylink, it passed into the public domain in 1997.
DiffServ (Differentiated Services)
A protocol that helps support network quality of service. DiffServ enables data packet fields to carry information about the specific level of service a packet should receive on the network.
digital
Of or related to the representation, transmission or storage of information in the form of strings of binary digits — rather than in the form of a continuously varying signal (i.e., analog form). See analog.
Digital Access Signaling System (see DASS)
Digital Access Signaling System 2 (see DASS2)
digital audiotape (see DAT)
Digital Cellular Service 1800 (see DCS-1800)
digital certificate
An encrypted code issued to two or more parties by a certification authority, and used to verify these parties' identities through the exchange of their public keys. See certification authority.
digital cross-connect system (see DCS)
Digital Data Network (see DDN)
digital data service (see DDS)
Digital Data Storage (see DDS)
digital divide
The lack of opportunities experienced by those with limited accessibility to technology, especially the Internet. This includes, but is not limited to, accessibility challenges in the following areas:
• Cultural (e.g., membership of a community that prohibits or restricts access to technology)
• Physical (e.g., having a disability that make it difficult or impossible to use a computer)
• Economic (e.g., being unable to afford a computer)
• Educational (e.g., not knowing how to use a computer)
Digital Enhanced Cordless Telecommunications(see DECT)
Digital Imaging and Communications in Medicine (see DICOM)
digital linear tape (see DLT)
digital mock-up (see DMU)
digital modem
A modem used for digital, rather than analog, data transmission. Examples include the digital subscriber line (DSL) and cable modems used for high-speed Internet access. See modem, cable modem and DSL modem.
digital network
A network incorporating both digital switching and digital transmission.
Digital Private Network Signaling System (see DPNSS)
digital rights management (see DRM)
digital signal
A discrete or discontinuous signal; one whose various states are discrete intervals apart.
Digital Signal Cross-Connect Level 1 (see DSX-1)
Digital Signal Cross-Connect Level 3 (see DSX-3)
Digital Signal Level 0 (see DS0)
Digital Signal Level 1 (see DS1)
Digital Signal Level 3 (see DS3)
digital signal processor (see DSP)
digital signature
A core component of a public key infrastructure (PKI) security installation. A digital signature can prove identity because it is created with the private key portion (which only the key holder should access) of a public/private key pair. Anyone with the sender's widely published public key can decrypt the signature and, by doing so, receive the assurance that the data must have come from the sender (nonrepudiation of the sender) and that the data has not changed (integrity). The data that is encrypted with the private key is not the entire message, but a short, fixed-length block of data that is computed from the message using a so-called "hash" function. See PKI.
Digital Signature Algorithm (see DSA)
digital subscriber line (see DSL)
digital subscriber line access multiplexer (see DSLAM)
digital subscriber line modem (see DSL modem)
digital television (see DTV)
digital-to-analog converter (see DAC)
digital versatile disc (see DVD)
digital versatile disc read-only memory (see DVD-ROM)
digital videodisc (see DVD)
Digital Video Interface (see DVI)
digitization
The conversion of paper-based or analog information into a digital data format.
digitizer
Input technology that digitally captures handwritten letters or images recorded with a pen or stylus on an electronic pad (for example, in a personal digital assistant or tablet PC).
DIMM (dual in-line memory module)
A memory packaging form factor that allows for a wider data path to memory, higher memory capacities in systems, and potentially easier upgrading than traditional single in-line memory modules (SIMMs). See SIMM.
DIN (Deutsches Institut fur Normung)
A German standards body. The acronym is also the common name of a multipin connector format defined by this body. DIN connectors are often used in computer hardware such as PCs and notebooks.
DIP (dual in-line package)
A method of packaging electronic components for mounting on printed circuit boards.
direct-access storage device (see DASD)
direct-attached storage (see DAS)
direct broadcast satellite (see DBS)
direct dial
The ability to place calls directly to an extension, bypassing the switchboard operator.
direct distance dialing (see DDD)
direct memory access (see DMA)
Directory Access Protocol (see DAP)
Directory-Enabled Networks (see DEN)
Directory Interoperability Forum (see DIF)
directory service
A service that maps logical names to physical addresses in a network. In addition to address naming, directory services include network resource location and mapping.
Directory Services Markup Language (see DSML)
Directory XML (see DirXML)
direct-sequence spread spectrum (see DSSS)
DirXML (Directory XML)
A version of Extensible Markup Language (XML) offered by Novell for enterprisewide directory integration. DirXML uses XML formats in a metadirectory store of data common to all directories.
disaster recovery
Methods and procedures for returning a system, network or data center to full operation after a catastrophic interruption — including the recovery of lost data, the use of alternative network channels if the primary channels are disconnected or malfunctioning.
disaster recovery planning (see DRP)
discrete cosine transform (see DCT)
discrete manufacturing
The production of a discrete category of goods (such as automobiles, aircraft, computers or component assemblies).
discrete multitone (see DMT)
Disk Array Enclosure (see DAE)
disk drive
A computer device that reads from, and stores information on, a floppy or hard disk.
disk mirroring
The duplication of disks and controllers so that two access paths exist in case a failure occurs on one of them.
Disk Operating System (see DOS)
distance learning (see distributed learning)
Distance Vector Multicast Routing Protocol (see DVMRP)
distortion
An unwanted change in a waveform that occurs between points in a transmission system.
distributed component architecture (see DCA)
Distributed Component Object Model (see DCOM)
distributed computing
A form of computing in which data and applications are distributed among disparate computers or systems, but are connected and integrated by means of network services and interoperability standards so that they function as a single environment. See DCE (distributed computing environment).
Distributed Computing Environment (see DCE)
distributed computing environment (see DCE)
distributed control system (see DCS)
Distributed Data Architecture (see DDA)
distributed database
A database whose objects (tables, views, columns and files) reside on more than one system in a network, and can be accessed or updated from any system in the network.
distributed database management system (see DDBMS)
distributed data management
A form of client/server computing in which some portion of the application data executes on two or more computers.
Distributed File System (see DFS and Dfs)
Distributed interNet Applications (see DNA)
distributed learning
The distribution of the learning environment across boundaries of time and space (also known as "distance learning"). Distributed learning includes e-learning (the network-enabled delivery of digital learning content), but also includes other types of learning that don't involve computers. For example, correspondence courses and classes taught via videotape or closed-circuit television are forms of distributed learning. See e-learning.
distributed lock manager (see DLM)
Distributed Management Environment (see DME)
Distributed Management Task Force (see DMTF)
distributed memory parallel processor (see DMPP)
distributed output management (see DOM)
distributed processing
The ability of an application to run on one or more nodes of a multiplatform network. The user need not be aware of the physical location of the data or the application software. The application can operate using cooperative processing, but this condition is not necessary. See cooperative processing.
Distributed Relational Data Architecture (see DRDA)
Distributed System Object Model (see DSOM)
distributed systems
Computer systems in multiple locations throughout an enterprise working in a cooperative fashion. The system at each location serves the needs of that location but also is able to receive information from, and supply information to, other systems within the network.
distributed system management (see DSM)
distributed transaction processing (see DTP)
distribution and logistics
A category of product distribution management and warehousing functions that includes physically moving parts, components, spares and products between two or more locations. The processes involved include rating and routing of both inbound and outbound freight, tracking and tracing of shipments, freight bill payment and auditing, import and export compliance and documentation, and load optimization. Advanced concepts utilize logistics modeling, financial optimization and third-party logistics management tools.
distribution channel
A selling channel supported by an enterprise. Distribution channels may include retail sales, distribution partners, original equipment manufacturers and Internet channels.
distribution management system (see DMS)
distribution requirements planning (see DRP)
DL (see distributed learning)
DLEC (data local-exchange carrier)
A local-exchange carrier (LEC) that specializes in broadband data services, such as digital subscriber line (DSL) service. In the late 1990s, many believed that DLEC service would be a booming market; by 2001, however, as DSL growth fell short of expectation, it became clear that DLEC business model was unlikely to be a commercially viable one. See LEC and DSL.
DL/I (Data Language I)
The language in which application programmers specify requirements to IBM's Information Management System Database Manager (IMS DB). See IMS and IMS DB.
DLL (dynamic link library)
A Windows mechanism that links executable code modules to an application program or process. A DLL is loaded at runtime by the application or process that invokes it.
DLM (distributed lock manager)
A mechanism used to synchronize data access and updates in a shared-disk cluster to ensure transaction integrity and data consistency. See cluster.
DLSw (Data Link Switching)
An IBM-developed technique for carrying Systems Network Architecture (SNA) traffic over a Transmission Control Protocol/Internet Protocol (TCP/IP) network. DLSw "tunnels" or encapsulates SNA traffic using the transport services of TCP/IP. See SNA and TCP/IP.
DLT (digital linear tape)
A linear recording tape drive designed by Digital Equipment and sold to Quantum in 1993. The technology became a de facto standard for backup and archive applications in 1997.
DM (see data mart)
DMA (direct memory access)
A facility in a computer's processor architecture that permits data to be sent directly to or from system memory without passing through the processor's general registers.
DME (Distributed Management Environment)
A mix of network management specifications introduced by the Open Software Foundation (OSF) in the early 1990s. See OSF.
DMI (Desktop Management Interface)
An architecture specification defined by the Distributed Management Task Force (DMTF), designed to give vendors and users a common vendor- and protocol-neutral framework to manage desktop systems, servers, peripherals and components. See DMTF.
DML (data manipulation language)
A set of commands used by a Structured Query Language (SQL) programmer to access and manipulate data. See SQL.
DMPP (distributed memory parallel processor)
A massively parallel processing system without shared-memory capabilities; also known as "loosely coupled."
DMS (distribution management system)
Another term for warehouse management system (WMS). Some people use the term DMS because the system is used to control the activities within a distribution center. See WMS.
DMT (discrete multitone)
A frequency division method for transmitting data over twisted-pair lines using 256 frequencies in the 64 kilohertz to 1.1 megahertz range. Used in digital subscriber line (DSL) service, DMT is a sophisticated signaling method, with robust error correction and bandwidth management features. See DSL.
DMTF (Distributed Management Task Force)
An industry organization (formerly known as the Desktop Management Task Force) promoting the development, adoption and unification of management standards and initiatives for desktop, enterprise and Internet environments.
DMU (digital mock-up)
A 3-D application used to simulate mechanical designs.
DMZ (demilitarized zone)
Technical jargon for the protected subnet between an intranet and the public Internet.
DNA (Distributed interNet Applications)
A Microsoft application development framework.
DNAfs (Distributed interNet Applications for Financial services)
An application development framework from Microsoft that contains industry-neutral object libraries, along with financial-services-specific extensions and logic. The extensions support industry standards (such as Open Financial Exchange), while the logic includes standard definitions for various transaction participants.
DNA-M (Distributed interNet Applications for Manufacturing)
A Microsoft development framework for manufacturing applications, including plant system integration and supply chain planning.
DNIS (Dialed Number Identification Service)
A feature of toll-free phone service that identifies the number a caller dialed to place an incoming call. DNIS is typically used when multiple organizations share common call facilities that can be reached through multiple toll-free numbers.
DNS (Domain Name System)
The system that serves as the map between logical names and network addresses in an Internet Protocol (IP) network. See IP.
DOCSIS (Data-Over-Cable Service Interface Specification)
A set of communications and operations support specifications for residential cable modem technology. Developed by vendors in the U.S. cable technology industry, DOCSIS has been accepted as a worldwide standard by the International Telecommunication Union. More than 90 percent of the world's cable modems are DOCSIS-compliant.
document component management (see DCM)
Document Content Description (see DCD)
document imaging
The conversion of paper documents into digital images through the use of a scanner or similar device, and the storage and management of electronic documents created through this process.
document management
A function in which applications or middleware perform data management tasks tailored for typical unstructured documents (including compound documents). It may also be used to manage the flow of documents through their life cycles.
Document Object Model (see DOM)
document type definition (see DTD)
DOM (distributed output management)
Middleware that drives the output process and supports the automated creation and delivery of documents. Key DOM capabilities include the ability to deliver documents to hard-copy output devices, such as printers or fax machines, as well as electronically via e-mail or Web servers.
DOM (Document Object Model)
A language-neutral interface from the World Wide Web Consortium, designed to enable programs and scripts to dynamically access and update the content, structure and style of documents.
domain
A group of nodes on a network that form an administrative entity. In the Internet naming hierarchy, a domain is a grouping of networks based on organization type or geography.
domain name
A unique identifier for an Internet site or Internet Protocol (IP) network address, consisting of at least two segments separated by periods. Enterprises must register top-level domains with the Web Internet Registry and pay a yearly fee to maintain the registry.
Domain Name System (see DNS)
DoS (denial of service)
The inability of a Web site or other server to respond to legitimate connections. DoS attacks are used to block access to a target Internet site.
DOS (Disk Operating System)
A command-driven PC operating system (OS) that resides in main memory and uses disks for data storage. It was once the standard OS for IBM-compatible PCs. Early versions of Microsoft Windows ran on top of DOS.
dot-com
Slang term for a company that conducts all or most of its business over the Internet. The term derives from the ".com" characters that appears at the end of many commercial Web site addresses.
dots per inch (see dpi)
double-byte character set (see DBCS)
double supertwisted nematic (see DSTN)
downlink
The portion of a satellite circuit extending from the satellite to the earth.
download
The process of copying a file onto a computer through a network, typically from a server or other computing device. Download times can be greatly affected by the transmission speed of a network connection.
Download Fun
A specification that supports secure downloading of consumer-oriented content using Internet-enabled mobile devices. Developed by Openwave, Download Fun is part of the GSM Association's Mobile Services (M-Services) initiative. See M-Services.
downtime
The total time a system is out of service.
DP (see data processing)
DPI (deep packet inspection)
An advanced form of firewall technology that looks deeper into the packet stream than traditional packet inspection approaches to identify attempts at malicious behavior and block them. DPI uses capabilities such as signature inspection to look for known attacks, recognize "normal" traffic and block protocol anomalies.
dpi (dots per inch)
A measurement of image resolution; for example, the number of pixels per inch on a cathode-ray tube (CRT) display. See CRT.
DPNSS (Digital Private Network Signaling System)
A standard developed by British Telecommunications and other U.K. private branch exchange (PBX) suppliers. It enables PBXs from different vendors to be connected with E1 lines to pass calls transparently between each PBX. See E1 and PBX.
DR (see disaster recovery)
DRAM (dynamic random-access memory)
A computer memory chip that requires electronic refresh cycles to preserve data stored for manipulation by logic chips.
DRDA (Distributed Relational Data Architecture)
An architecture for enterprisewide data access, introduced by IBM in 1990. It was designed to homogenize data definition and access across IBM's different hardware and software platforms.
DRM (device relationship management)
Technology to automate the management and reporting of remote devices — anything from a photocopy machine to the refrigerated trailer in a truck — through the capture and use of real-time information.
DRM (digital rights management)
Trusted exchange of digital information over the Internet whereby the user is granted only the privileges that the document sender allows.
DRP (disaster recovery planning)
Planning to ensure the timely recovery of information technology assets and services following a catastrophe, such as fire, flood or hardware failure. As such planning is increasingly coordinated with broader business recovery plans that go beyond IT, it is now commonly referred to as business continuity planning (BCP). See BCP.
DRP (distribution requirements planning)
The process of assessing the locations from which products should be deployed, and developing local-level stock replenishment plans.
DS0 (Digital Signal Level 0)
A standard 64-kilobit-per-second signal or channel carried over a T-carrier or E-carrier digital telecommunications facility. (Also presented as DS-0.) See T-carrier, E-carrier and DSx series.
DS-0 (see DS0)
DS1 (Digital Signal Level 1)
An arrangement for carrying multiple signals over a digital telecommunications line. DS1 (also presented as DS-1) is used to multiplex 24 DS0 channels into one 1.544 megabit per second (Mbps) T1 line (in the United States), or 32 DS0 channels onto one 2.048 Mbps E1 line (in Europe). See DS0, T1 and E1.
DS-1 (see DS1)
DS3 (Digital Signal Level 3)
An arrangement for carrying multiple signals over a digital telecommunications line. DS3 (also presented as DS-3) is used to multiplex 672 DS0 channels onto a 44.736 megabit per second (Mbps) T3 line (in the United States), or 480 DS0 channels onto a 34.368 Mbps E3 line (in Europe). See DS0, T3 and E3.
DS-3 (see DS3)
DSA (Digital Signature Algorithm)
An encryption algorithm for digital signatures, developed by the National Institute of Standards and Technology (NIST) for use with NIST's Digital Signature Standard. See digital signature.
DSA (Dynamic Scalable Architecture)
A database server architecture offered as part of IBM's Informix Dynamic Server product line, designed to help enterprises manage increasingly large and complex databases while improving overall system performance and scalability.
DSL (digital subscriber line)
An "always-on" access technology that uses public switched telephone network (PSTN) infrastructure to offer high-speed access to the Internet. The technology exploits the unused capacity of the twisted-pair copper wire used in the PSTN. Various types of DSL technology include asymmetric DSL (ADSL), high-bit-rate DSL (HDSL), symmetric DSL (SDSL) and very-high-bit-rate DSL (VDSL). The whole group is sometimes referred to as "xDSL." See ADSL, HDSL, SDSL and VDSL.
DSLAM (digital subscriber line access multiplexer)
A traffic aggregation device that multiplexes upstream and downstream information in a digital subscriber line (DSL) network. In most cases, the DSLAM is located in the central office (CO) and connects to the CO switch to support analog voice service. On the network side, the DSLAM can interface with asynchronous transfer mode (ATM), Internet Protocol (IP) or another broadband service. On the local-loop side, it supports various types of DSL or a remote-access multiplexer (MUX). See DSL, ATM, IP, CO and MUX.
DSL modem (digital subscriber line modem)
An access device that enables computer equipment to connect to the Internet and other network services over the public switched telephone network, using digital subscriber line (DSL) technology. See modem and DSL.
DSM (distributed system management)
Processes or technology for managing distributed systems. DSM tools are capable of dealing with a limited number of distinct elements and require a strong directory.
DSML (Directory Services Markup Language)
An extensible markup language (XML) vocabulary for working with Lightweight Directory Access Protocol (LDAP) directories. DSML development is overseen by a working group of the Organization for the Advancement of Structured Information Standards (OASIS). The first version provided a format for representing the structure of a directory as an XML document, so that clients could read the directory using XML. Version 2 also supplies XML formats for directory queries, protocol bindings, operations on a directory and the results of these operations. Since version 2 implements LDAP using XML, it can bring LDAP functionality to clients that are incompatible with LDAP (such as mobile devices) or unable to access LDAP directories through firewalls. See XML, LDAP and OASIS.
DSOM (Distributed System Object Model)
An object-oriented technology introduced by IBM in the mid-1990s. It never evolved into a commercially successful product.
DSP (digital signal processor)
A specialized computer chip optimized for high data rates needed to process digitized wave forms, particularly those derived from analog sources. Often used in equipment requiring voice digitization.
DSS (decision support system)
A system designed to support strategic (vs. operating) decisions. DSSs tend to be user-friendly and emphasize ad hoc query, reporting and analysis capabilities.
DSSS (direct-sequence spread spectrum)
A technology for third-generation wireless LAN (WLAN) systems. DSSS is a type of spread-spectrum technology, which enables multiple signals to share a single radio band. It has the ability to deliver twice the bandwidth per node, per access point than frequency-hopping spread spectrum (FHSS) and is more resilient to certain types of multipath interference. See FHSS and WLAN.
DSTN (double supertwisted nematic)
A type of flat-panel display screen.
DSU (data service unit)
A simplified modem for the transmission of digital data over a private line or for limited-distance communications over the public switched telephone network (PSTN), where it is not necessary to comply with all the requirements for a high-speed modem.
DSx series (Digital Signal Level x series)
In the T-carrier and E-carrier systems, a series of digital signal levels (with "x" representing the level number), each providing a specific number of channels over a specific bandwidth. See DS0, DS1, DS3, T-carrier and E-carrier.
DSX-1 (Digital Signal Cross-Connect Level 1)
A standard electrical interface used to cross-connect T1 digital telecommunications lines and equipment running Digital Signal Level 1 (DS1) service. See T1 and DS1.
DSX-3 (Digital Signal Cross-Connect Level 3)
A standard electrical interface used to cross-connect T3 digital telecommunications lines and equipment running Digital Signal Level 3 (DS3) service. See T3 and DS3.
DTD (document type definition)
Document grammar defined in Extensible Markup Language (XML), describing an XML document's data elements and markup tags, along with any other defined data element attributes. Using a DTD, an XML parser can validate a document for conformance to a particular document type. See XML.
DTE (data terminal equipment)
End-user devices — such as terminals and computers connected to data communications equipment (DCE) — that either generate or receive the data carried by a network. In the Electronic Industry Alliance's RS-232 specification, designation as DTE or DCE determines the signaling role in handshaking. See RS-232.
DTMF (dual-tone multifrequency signaling)
The basis for operation of touch-tone telephones. DTMF is a method of signaling in which a matrix combination of two tones is used to transmit numerical information.
DTP (see desktop publishing)
DTP (distributed transaction processing)
Transaction processing using distributed systems, rather than mainframes. A DTP monitor is a transaction-processing monitor (TPM) that serves as a middleware component, helps manage distributed servers on the network, and aids programmers by making the location of services transparent and decreasing their need to deal with database and low-level network protocols. The word "distributed" often qualifies "TPM" to denote that this component is a network tool rather than a mainframe one. However, the mainframe environment is where TPMs were first developed. See transaction processing and TPM.
DTV (digital television)
Technology for broadcasting and viewing digital television signals. Such technology includes DTV sets, which are specially designed to receive, demodulate and decompress digital terrestrial television signals, and provide complete systems for receiving and viewing digital entertainment.
dual in-line memory module (see DIMM)
dual in-line package (see DIP)
dual-tone multifrequency signaling (see DTMF)
dumb terminal
A terminal that does not perform local processing of entered information, but serves only as an input/output device for an attached or network-linked processor.
dump
As a verb or noun, refers to the transfer all information from a stored record to another storage medium for output device — for example, outputting data from a file to a printer.
DUNS (Data Universal Numbering System)
A system of classification that uses a nine-digit number assigned by Dun and Bradstreet Information Services to identify unique business entities.
duplex
A form of data transmission in which signals travel in both directions simultaneously (also known as "full duplex"). See half duplex and simplex.
DVD (digital versatile disc)
An optical disk (also known as a "digital videodisc") with the ability to store several gigabytes of data.
DVD-ROM (digital versatile disc read-only memory)
A read-only digital versatile disc (DVD) format designed specifically for the PC market. DVD-ROMs are the same size as compact disc read-only memory (CD-ROM) discs, but are loaded much more densely with data, with storage capacities starting at 4.7 gigabytes. See DVD and CD-ROM.
DVI (Digital Video Interface)
A specification for a computer monitor interface capable of carrying both analog and digital signals. DVI was developed by the Digital Display Working Group, an industry group formed by Intel and other vendors. DVI connectors can be used for analog monitor technologies such as cathode-ray tube (CRT), as well as digital ones such as liquid crystal display (LCD). For LCD displays, the use of a digital interface is needed to ensure a quality image and minimize setup requirements. See CRT and LCD.
DVMRP (Distance Vector Multicast Routing Protocol)
A protocol used for Internet Protocol (IP) multicast routing. See IP multicast.
DW (see data warehouse)
DWDM (dense wave division multiplexing)
A technology used to increase fiber-optic transmission capacity (also called wave division multiplexing, or WDM). In fiber-optic networks such as Synchronous Optical Network (SONET), DWDM permits fibers to carry up to eight wavelengths of light, thus multiplying their capacity by the number of wavelengths carried. DWDM has been applied to a number of international submarine optical cables to increase capacity. See fiber optics and SONET.
DXI (data exchange interface)
A standard interface enabling customer premises equipment (such as routers) to access an asynchronous transfer mode (ATM) or Switched Multimegabit Data Service (SMDS) network. See ATM and SMDS.
dyadic
A multiprocessor design term that IBM introduced with the 3081 Processor Complex. In the dyadic design, two processors share storage and operated under a single control program.
dynamic bandwidth allocation
The process of monitoring the traffic loads over a communications channel, and automatically increasing or decreasing the bandwidth of the channel to optimize overall network utilization efficiency.
dynamic content
Web site content that is continually refreshed to provide new or updated information to attract new viewers and to keep prior viewers returning to the site.
Dynamic Data Exchange (see DDE)
Dynamic Domain Name System (see DDNS)
Dynamic Host Configuration Protocol (see DHCP)
Dynamic HTML (see DHTML)
dynamic link library (see DLL)
dynamic RAM (see DRAM)
dynamic routing
A method of network transmission that uses a router to select the most appropriate path for each section of data packet transmission along a network.
Dynamic Scalable Architecture (see DSA)
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