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A glossary of terms important to IBM mainframe machines

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DA/2:  Distributed Application/2. OS/2 software providing a set of APIs for building client/server applications. The APIs hide the complexity of underlying communications (APPC, NetBIOS, Named Pipes, etc). Supports CID, CICS, IMS1, APPC. Withdrawn December 2000.

DACTLINK:  Deactivate link.

DACTLU:  Deactivate logical unit.

DACTPU:  Deactivate physical unit.

DACU:  Device Attachment Control Unit. See 7171.

DADSM:  Direct Access Device Space Management. Space allocation software within DFSMSdfp.

DAE:  Distributed Automation Edition. Set of tools, services, and interfaces for developers to use to create factory-floor applications. Announced February 1989. One by one, it has all been withdrawn over the years.

Daemon:  An event-driven process, implemented as a memory-resident program that remains in the background until an event of interest occurs, then jumps into action. The term is most commonly used in the Unix environment.

DAISY:  Dynamically Architected Instruction Set. A VLIW software translator which can convert Java code and PowerPC machine code. Not a product but a prototype developed at IBM’s research center at Yorktown, which began working on VLIW techniques in 1986.

DAN:  Direct Attachment Node.

DARI:  Database Application Remote Interface. A stored procedure API supported by DB2 CS.

Dark fiber:  A fiber optic cable path without any repeaters for reamplification in between.

DARPA:  Defense Advanced Research Projects Agency. Formerly called the Advanced Research Projects Agency, DARPA is the US Department of Defense agency responsible for creating ARPAnet.

DASD:  Direct Access Storage Device. IBMspeak for disk. When RAMAC RAID was announced, it looked like IBM had finally capitulated to the word Disk, but it was not to be.

DASD farm:  Term coined as sites started to install huge amounts of DASD, and to manage all the DASD as a single data resource – the DASD farm. The confines of the farm are rather indistinct, but it normally stretches from the processor side of any storage control devices to the slowest layer on the storage hierarchy, which does not normally contain DASD per se. See also Information warehouse.

DASD Fast Write:  Facility introduced on the 3990-3 to improve the writing performance of DASD. Data is written to cache and non-volatile storage in the DASD controller, which then writes it to disk at its leisure, thereby removing the need for a program to wait for data to be written to disk before it can continue. Fast Write extends the range of datasets which can be considered for caching, and improves performance by about 28%. Key feature when it was introduced, since the ability to write data very quickly is essential to a memory-based computing environment. See also SSD1, Cache Fast Write.

DASF:  Dual Address Space Feature. Facility in z/OS enabling a user to connect a secondary address space to a program, notably in JES3. A very similar feature appears to have been used to create z/OS dataspaces and Hiperspaces. See also Dataspace1.

DAT:  Dynamic Address Translation. The process by which virtual addresses are converted into real addresses during instruction execution.

Data Analyst:  See Bachman.

Data Analyzer:  A Microsoft Office visualization and analysis product announced November 2001 and sold separately, rather than being a part of any Office XP offering.

Database/2:  See DB2.

Database Administration Tools:  A set of DB2 utilities. A member of the Data Management Tools for DB2 family, announced September 2000 as a replacement for DB2 Utilities. See also Database Recovery and Replication Tools.

Database Manager:  The IBM-developed database manager originally available only as part of the OS/2 EE bundle until early 1991, when it became available separately. The unbundled version was renamed DB2/2 in January 1993.

Database memory:  Feature on the eserver pSeries which uses a combination of hardware and software to allow related transactions to be grouped as a single atomic transaction; it’s meant to help recovery/restart after a crash.

Database Navigator:  An OS/400 Operations Navigator GUI that displays the relationship among relational objects such as tables, views, and indexes.

Database Recovery and Replication Tools:  A set of DB2 utilities. A member of the Data Management Tools for DB2 family, announced September 2000 as a replacement for DB2 Utilities. See also Database Administration Tools.

Datablazer:  Range of fixed and removable storage devices announced for the OEM market early 1993. Given to Xyratex when it was founded in a management buyout (MBO) from IBM in 1994. Obsolete.

Data Class:  One of the SMS1 storage management classes. Data Class defines the physical characteristics of a dataset.

Data Dictionary:  A data dictionary (DD) is a database which contains information about the way items of data are used. Typically a DD contains details of data names, data usage, data structures, data models, and so on. IBM’s eponymous Data Dictionary was never appreciated in a marketplace dominated by third-party products.

Data flow control:  Layer 5 of SNA; manages the logical sessions over a single connection between two locations.

DatagLANce:  IBM system administration tool for Ethernet and Token Ring LANs, announced October 1993. Provides facilities for the collection of LAN statistics in real time, and can be used for application software debugging, capacity planning, network reconfiguration, and internetwork trouble-shooting. Withdrawn March 1995.

Datagram:  Generic term for a transmission method used in packet switched networks in which sections of a message are transmitted in an arbitrary order and then re-assembled by the recipient. Each datagram packet is sent without any regard to previous or subsequent packet. Typically individual datagrams are not explicitly acknowledged.

DataGuide:  Information Warehouse software (vintage October 1993). Creates and searches a catalog of information on all databases using various extract tools. Originally for accessing DB2 on z/OS and OS/2 only, but support for OS/400 and AIX was added December 1995. DataGuide for Windows and DataGuide for Lotus Notes were announced October 1994 then withdrawn March 1996. DataGuide Version 1.1 was announced December 1995 for Windows and OS/2 clients to DB2 on OS/2, AIX, OS/400, z/OS and Windows 95/NT. In May 1998, it was replaced by Visual Warehouse, which became part of DB2 Enterprise Edition then DB2 Universal Database.

DataGuide Tags:  An IBM technology for storing and sharing metadata.

Data heap:  A term used in Unix and AIX to refer to a section of memory set aside to store a specific type of data.

DataHub:  DBMS product set (full name SystemView Information Warehouse DataHub) of database tools which provides a workstation-based control point for database management. Includes MVS, VM, OS/400, RS/6000, and OS/2 (DB2/2) host components, plus a workstation component. First emerged in September 1992 when various vendors (including Candle, Platinum, and Legent/CA) promised that they would support DataHub. Withdrawn October 1995.

Data integrity:  The knowledge that information has been unaltered during transmission or storage.

DataInterchange:  See expEDIte.

Data Interpretation System:  See DIS2.

DataJoiner:  IBM Information Warehouse Software for AIX, announced October 1994. Provides transparent SQL access to data on relational and non-relational databases on a number of platforms. HP-UX version announced June 1996. DB2 version announced September 1997. Version 2.1.1 was announced July 1998, running on AIX, Windows NT and Sun Solaris, leaving HP-UX users still supported by marooned at June 1996’s Version 1.1. The iSeries 400 with the Integrated PC Server (IPCS) is also supported with the NT version.

DataJoiner Classic Connect:  Expands DataJoiner access to IMS1 and VSAM data. Announced July 1996. Replaced by Classic Connect July 1999.

Data link:  A physical link, e.g., a wire or a telephone circuit, that connects devices or communications controllers. Specified in layer 2 of the OSI reference model. See OSI layer.

Data link control:  Layer 2 of SNA; manages the physical connection between two locations.

Data Link Switching:  See DLS3.

Data Management Tools for DB2:  A family of DB2 utilities, announced September 2000 as a replacement for DB2 Utilities. Includes Database Recovery and Replication Tools and Database Administration Tools.

Data Mart:  Storage of the data required to meet the information needs of a department or group of users. Typically read-only. Optimized to satisfy their query and/or reporting needs.

Data mining:  The practice of using a data warehouse for highly complex, ad hoc queries. Data mining and data warehousing have become synonymous in the hearts and brochures of most database salesmen.

Data Propagator:  Became one word in more recent versions. See DataPropagator.

DataPropagator:  z/OS program developed in association with the Swiss Bank Corporation, and announced September 1990 as Data Propagator (later made into one word). Initially it automatically copied changes in an IMS database to a DB2 database using a two-phase commit protocol so that the end-user DB2 database could be kept in sync with the production IMS database. A bi-directional version which propagated changes either from DB2 to IMS or from IMS to DB2 was announced in March 1993 looking suspiciously like a migration aid from IMS to DB2. A version which allowed parts of a mainframe database to be replicated (in read-only form) on OS/2 workstations was announced in October 1993, AS/400 implementations in April 1994, and an HP-UX version in February 1995. Withdrawn October 1995. Also known as DPROP. See also TPFDDA.

DataRefresher:  GUI-based software (October 1993) which moves large amounts of data from databases and flat files to refresh relational databases from existing MVS relational and non-relational applications. Uses a client/server paradigm based on an OS/2 client. Supports IMS/ESA, DB2 (under MVS, VM, OS/2, and RS/6000) flat files, and various non-IBM files. Replacement for DXT. Withdrawn April 1999.

Data Sciences:  UK system/software integrator bought by IBM in March 1996.

Data Security Monitor:  An auditing tool that comes with RACF. Reports on the status of resources that RACF controls.

Dataserver:  See 3995.

Dataset1:  A unit of data storage and retrieval consisting of one or more data records. Outside of the IBM mainframe environment, people call them files.

Dataset2:  AT&T term for a modem – presumably in contrast to a handset.

Dataset profile:  A profile used by RACF to protect one or more datasets.

Dataspace1:  Areas of storage (up to 2GB) accessible to mainframe programs for storage and retrieval of data. In effect, the dataspace concept is a mapping facility which allows the user to pretend that he has loads more central storage (16 terabytes under MVS/ESA) than he actually has.

Dataspace2:  Within MVS VSAM, the area on a disk allocated to a VSAM catalog on which VSAM datasets can be placed.

DataStage:  Software from Ascential Software announced marketed by IBM beginning September 2001. Works with DB2 Warehouse Manager to bring together multi-platform data.

Data striping:  A technique for achieving parallel transfer of data by splitting up data across a number of devices and transferring parts of sets of data in parallel. See File striping, Disk striping.

Data Tables:  CICS feature announced March 1989 which allowed heavily used data to be held in CICS controlled main storage above the 16MB line. Gave substantial performance improvements by reducing I/O. Shared Data Tables were announced in March 1992, and gave massive improvements (up to 70% for local reads) compared to VSAM. Part of the Data In Memory (DIM) philosophy.

DataTrade:  A set of IBM communications programs – announced April 1990 – designed to provide a consistent API for data transfer between distributed applications on processors running different IBM operating systems. Available for PS/2, RS/6000, and System/88. Each program is in two parts, a Manager in a server, and a Workstation Feature in a workstation. Withdrawn between mid 1992 and mid 1994.

Data Warehouse:  General term for a collection of database, middleware, and query tools that allow fast, flexible access to near-operational corporate data. Data warehousing has proved invaluable in industries such as retail for tracking buying patterns and forecasting future customer requirements. It has also provided a handy marketing tool for database vendors trying to breathe new life into their products.

Data Warehouse Center:  Provides a data warehouse creation and management GUI. Handles tasks such as registering and accessing data sources, and defining data extraction and data transformation steps. Part of DB2 Warehouse Manager and integrated with DB2 Control Center.

DAT box:  A hardware feature of some System/360 and most System/370 systems that translated virtual into real addresses. Mention of the DAT box brings nostalgic tears to the eyes of hoary old systems programmers and to the eyes of the DP managers who bought $200,000 DAT boxes in 1970 only to find DAT as a standard 370 feature two years later. No one talks about them anymore, but they are standard equipment in all IBM mainframes since the 370. Virtual memory and paging would be impossible without it.

DATE:  Dedicated Access to X.25 Transport Extension. SNA facility for handling X.25 packets. Configuration option under NPSI.

DB/DC:  DataBase/Data Communications. Generic name for on-line database system + TP monitor. IMS1 is an example, with IMS DB as the database and IMS TM as the monitor.

DB2:  Database/2. Relational database management system first announced for z/OS environments in 1983. Originally promoted as an end-user tool, but is now IBM’s preferred DBMS for just about everything apart from the legacy applications serviced by IMS1. DB2 became a family in the early 1990s and there are now DB2 versions, most under the name DB2 Universal Database, for a broad range of platforms. Since some began as other products, there were initial compatibility problems, they seem to have disappeared over the years. See also DB2 Universal Database, DB2 Server for VSE and VM, DB2 Everyplace.

DB2/2:  A renaming of OS/2 Database Manager in January 1993 when it was unbundled from OS/2 Version 2.0. The new version was a true 32-bit product, and included enhancements in performance, portability, DB2 and SQL compatibility, and systems management. Replaced by DB2 Universal Database.

DB2/400:  The SQL implementation on the AS/400. A subset of full IBM SQL, but a full implementation of the SAA version of SQL. Includes compilers for calls from high-level languages, and interactive options for table and file definition. Originally called SQL/400. Replaced by DB2 Universal Database.

DB2/6000:  The relational DBMS for the RS/6000 announced in March 1993. Built on top of the OS/2 DB2/2 code, but with industrial strength features more akin to mainframe DB2 – extensive locking, on-line optimizer, and performance management. Supports DDCS and DRDA, and enables the RS/6000 to act as a database server, perhaps in an Information Warehouse set-up. POWERparallel support announced April 1994 (see DB2 Parallel Edition for AIX). Replaced by DB2 Universal Database.

DB2/6000 Parallel Edition:  See DB2 Parallel Edition for AIX.

DB2/MVS:  The original DB2 incarnation first announced in 1983. Technically, SQL/DS was first, but DB2/MVS was the first to bear the DB2 name. Originally promoted as an end-user tool, but is now IBM’s preferred mainframe DBMS. Its key strength is the SQL interface which is now a de facto industry standard. A major re-vamp in March 1993 added Hiperpool, access to Asynchronous Data Mover Facility, improved partitioning, and better availability. Enhancements in Version 4 (announced October 1994) included support for parallel query, domain definition by users, and much better support for distributed processing. Version 5 (announced Nov 1996), which was supposed to be version 4.2, included much higher prices than users had expected. Replaced by DB2 Universal Database.

DB2/UX:  Mid 1995 implementation of DB2 for HP-UX. Shares a common code base with DB2/6000. Replaced by DB2 Universal Database.

DB2/VM:  A renaming (mid 1993) of SQL/DS for the VM environment. Renamed DB2 Server for VSE and VM May 1997.

DB2/VSE:  A renaming (mid 1993) of SQL/DS for the VSE environment. Renamed DB2 Server for VSE and VM May 1997.

DB2 buffer-pool tool:  IBM software that helps performance analysts tune DB2 relational databases, to optimize memory usage and I/O. Produces statistics for all pools and objects, simulation of changing pool sizes, prediction of effects of moving DB2 objects into new pools. Announced September 1997.

DB2 Catalog:  The set of tables within DB2 which maintain the descriptions of objects such as tables, plans, views, and indexes. See DBRAD.

DB2 Common Server:  Obsolete term for DB2 Universal Database.

DB2 Connect:  Middleware that runs on AIX, HP-UX, Linux, NUMA-Q, OS/2, Sun Solaris and Windows to enable applications running on those platforms to access DB2 data residing on z/OS, z/VM, VSE/ESA and OS/400. Announced September 1997.

DB2 Control Center:  A Java-based GUI that provides a single point of control and consistent procedures for managing DB2 systems on different platforms, including the mainframe. It can run directly on the workstation as a Java application or on a Web server and run through a Web browser.

DB2 CS:  See DB2 Common Server.

DB2 Estimator:  Originally a Windows and OS/2 software product for estimating resource requirements and modeling the performance of z/OS DB2 systems. Announced June 1994. Became a component of DB2 itself in December 1996.

DB2 Everyplace:  DB2 for mobile and embedded devices. Runs on Linux, Palm OS, QNX Neutrino, Symbian EPOC, Windows CE/PocketPC and Win32-based platforms. Has its own data store that can be used to store local data or data downloaded from elsewhere. The Sync Server component runs on AIX, Linux, Sun Solaris and Windows NT/2000/XP. It synchronizes the Everyplace data store with external databases on DB2 Universal Database for z/OS, iSeries 400, Unix, OS/2 and Windows, as well as Oracle, Microsoft SQL Server, Informix and Sybase.

DB2 Extenders:  Software that supports new DB2 data types. For example, DB2 XML Extender enables defining, accessing, storing, and searching data stored using the XML data type. See also Net Search Extender, Starburst.

DB2 Governor:  A component of DB2 which sets a CPU limit on queries to prevent users hi-jacking a machine. Also known as RLF (Resource Limit Facility).

DB2I:  DB2 Interactive. z/OS ISPF techie’s tool providing interactive access to DB2.

DB2ICF:  DB2 Integrity Control Facility. Programmer’s z/OS DB2 development tool running under ISPF.

DB2 Intelligent Miner:  See Intelligent Miner.

DB2 Parallel Edition for AIX:  Version of DB2/6000 announced in April 1994 along with the POWERparallel hardware. Decomposes complex queries into small parts which can be run in parallel. Also allows updates, index creation, and backup and restore to be run in parallel. Formerly known as DB2/6000 Parallel Edition. Replaced by DB2 Universal Database (UDB) December 1997.

DB2 PM:  DB2 Performance Monitor. Performance monitor for DB2 Universal Database for z/OS that produces all sorts of pretty colored pictures showing how much resource both it and DB2 are consuming. Now part of a family called IBM Tools for Database Performance Management. Other members include DB2 SQL Performance Analyzer, DB2 Query Monitor, IMS Performance Analyzer and IMS Queue Control Facility.

DB2 Server for VSE and VM:  The very first DB2 implementation was on VM and VSE in the early 1980s. But it was known as SQL/DS. Curiously, despite several renamings, it is now almost an orphan, being only one of two DB2 products not (yet?) given the Universal Database (UDB) moniker (DB2 Everyplace is the other).

DB2 Solaris:  Mid 1995 implementation of DB2 for Sun Solaris. Shares a common code base with DB2/6000. Replaced by DB2 Universal Database.

DB2 Sort Assist:  A standard feature of eserver zSeries 9000 that accelerates DB2 performance during sorting. Sorting is very common when processing SQL queries. See also Assist.

DB2 Text Extender:  See Text Extender.

DB2 UDB:  See DB2 Universal Database.

DB2 Ultralite:  Cut down version of DB2/2 once intended as a competitor for the likes of Microsoft’s Access and Borland’s Paradox in the OS/2 and Windows markets.

DB2 Universal Database:  With the exception of z/VM, VSE/ESA and mobile/embedded platforms, all DB2 implementations are known as DB2 Universal Database. Those platforms include z/OS, AIX, HP-UX, Linux, OS/2, NUMA-Q, Sun Solaris, Windows and iSeries 400. There is also the Satellite Edition, which runs on occasionally-connected remote systems running Windows. See also DB2, DB2 Server for VSE and VM, DB2 Everyplace.

DB2 Warehouse Manager:  A set of tools to build, manage and access data warehouses built in z/OS DB2 Universal Database. See also Data Warehouse Center.

DB2WWW:  DB2 World Wide Web Connection. First previewed June 1995, free software, downloadable from the Internet, which allows users to access DB2 data via the Internet using a web browser. Initially available for DB2 under AIX and OS/2, and promised for MVS, VM, and AS/400. Versions for Windows NT, Solaris, and HP-UX were announced mid 1996. A VM/ESA version was previewed in May 1997, two months after the same product name was used for a CBT course for Internet application developers. Nothing has been heard since.

DBA:  DataBase Administrator. The person who is responsible for a database system.

DBCS:  Double-Byte Character Set. Coding sets used for certain far-East languages, including Japanese and Korean. cf. SBCS, MBCS.

DBCTL:  DataBase ConTroL. z/OS facility which improves the interaction between subsystems (notably IMS and CICS) and multiprocessor performance.

DBEDIT:  DataBase EDIT. DB2 and SQL/DS editor, allegedly suitable for users without DP or relational database experience. Withdrawn March 1997.

DBICF:  IMS DataBase Integrity Control Facility. Set of inter-related programs and procedures, originally written by Swiss Bank Corporation, for simplifying recovery of IMS and CICS DL/I databases.

DBMAUI:  DB2 Migration Aid Utility. Withdrawn January 1993.

DBMS:  DataBase Management System. Generic term for a computer system, usually software-based, for storing and accessing data. IBM’s DBMSs include DB2 and IMS1, but not VSAM. Although VSAM has the ability to lookup records directly by key, it does not allow the definition of fields, a key feature of a DBMS.

DBPROTOTYPE II:  Design/prototyping tool for designing IMS databases. Withdrawn January 1989.

DBRAD:  DataBase Relational Application Directory – available as DBRAD/MVS and DBRAD/VM. A crude data dictionary for DB2, announced with DB2 Release 3, which was initially seen as a solution to the weaknesses of the DB2 Catalog. In fact, DBRAD was not a lot better than the Catalog itself; it’s little more than a Catalog front end which adds the ability to store and report data relationships, but is not a full data dictionary. Users say it’s cumbersome and incomplete. DBRAD/MVS was withdrawn January 1993. DBRAD/VM was not withdrawn until December 1997 in a purge of non-Y2K-compliant software.

DBRC:  DataBase Recovery Control. Originally an IMS tool for automating a large part of system recovery, but now used by DB2 as well. DBRC maintains logs and generates recovery job streams.

DBRM:  DataBase Request Module. Dataset containing source SQL code created by the DB2 pre-compiler. The SQL is removed from the source code of the program and replaced by calls to DB2 modules. The DBRM entry is used as input to the bind processor to create a plan which is stored with a time stamp in the database.

DBSYNC:  A free IBM utility that compares two RACF databases and generates the RACF commands to make them similar.

dbx:  Debugger for Unix programs, available for AIX1 and z/OS Unix System Services. Provides source-level debugging and services to debug C language programs in a multi-threaded environment.

DC:  Data Chaining.

DCA:  Document Content Architecture. Set of rules (machine-independent datastream) about document formats, meanings of control characters, handling of non-text material, etc. The objective of DCA is to enable any DCA hardware or software to receive and interpret any DCA document in the same way. Now incorporated within MO:DCA.

DCAF:  Distributed Console Access Facility. OS/2 facility (June 1990) which uses LU6.2 to enable an OS/2 workstation to control another DOS or OS/2 device across an SNA or gatewayed TRN network. Can transmit files, dump, or re-boot remote file servers and workstations. Works by receiving screens from, and controlling the keyboard of, the remote machine. Sold for Help Desk type applications. Replaced by Tivoli Remote Control July 1997.

DCB:  Device Control Block. The control block used to tie an z/OS application program to a non-VSAM dataset – the two are connected by the DDNAME.

DCC:  Data Country Code. A 3-digit code used in X.25, as a unique country identifier.

DCE1:  Data Control (sometimes Configuration, sometimes Circuit-terminating) Equipment. ITU-T term defining the network end of a link on the user’s premises; the other end is the DTE. A modem is a typical piece of DCE.

DCE2:  Distributed Computing Environment. An attempt by the IBM-backed OSF to create an independent standard for cooperative processing systems. Comprises standards for distributed services (name and directory services, remote procedure calls, etc), and data sharing services (distributed file system, PC integration, diskless operation). DCE was the basis of the CICS/6000 product. IMS support was announced in October 1993, AS/400 support in January 1994. By the middle of 1994, IBM had worked itself up into a state of great enthusiasm for it, and before long DCE support seemed to be in every IBM platform.

DCE Security Server:  A component of SecureWay Security Server that is integrated with RACF and provides a fully functional OSF DCE2 security server for z/OS Unix System Services (USS).

DCF:  Document Composition Facility. Mainframe text composition software consisting of a text formatter (SCRIPT/VS) and an environment feature. Works with ATMS III, DLF and PROFS, where it was one of the least liked features of the package (it was replaced by DisplayWrite/370 within PROFS, and nobody liked that much either). The emergence of CALS in the early 1990s gave DCF a new lease on life. Still supported in z/OS, z/VM and VSE/ESA but there has not been a new release in over a decade.

DCI:  Display Control Interface. Microsoft/Intel standard for multimedia and video software under Windows.

DCLGEN:  DB2 facility for creating COBOL or PL/I copybooks based on table definitions.

DCM1:  Dynamic Channel Path Management.

DCM2:  See Digital Certificate Manager.

DCME:  Dynamic Cache Management Enhanced. DB2 facility introduced after Version 3.0 for exploiting DASD cache controllers.

DCMF:  Distributed Change Management Facility.

DCollect:  DFSMSdfp utility for collecting data storage usage information.

DCOM:  Distributed COM. Obsolete since COM now supports both local and remote operation. See also COM, COM+.

DCSS:  DisContiguous Saved Segment. DCSS areas are bits of virtual storage in a z/VM system used to hold a single copy of shared code. The objective is to improve performance and reduce storage requirements.

DD1:  See Data dictionary.

DD2:  Data Definition. The MVS JCL statement used to associate a dataset with the application program processing element (e.g., ACB, DCB). The DD statement is characterized by its bewildering number of parameters with unusual spellings.

DDBMS:  Distributed DBMS. Generic term for a database system in which the physical data is distributed across different machines, but which presents a single database image to the user – i.e., it provides location transparency. Technically it’s extremely difficult, and no vendor has a complete solution. See DB2, DDF, DDM, Distributed Unit Of Work, DRDA, QMF, Remote Unit of Work, Two-phase commit.

DDCS:  Distributed Database Connection Services. Software which creates a transparent connection between a client workstation application (DOS, Windows, OS/2) and a DB2, SQL/DS, RS/6000, or AS/400 database server, allowing the client to read and update the database on the server. DDCS was a key implementation of the DRDA architecture. DDCS software was available from IBM for OS/2, AIX, HP-UX, and Sun Solaris. Replaced by DB2 Connect September 1997.

DDE:  Dynamic Data Exchange. Method in Windows and OS/2 Presentation Manager of transferring data in real time among applications. Supported in Easel. See also OLE.

DDF:  Data Distribution Facility (also Distributed Data Facility). LU6.2 facility for getting DB2 databases to talk to one another.

DDL:  Data Description/Definition Language. Generic term for a language used to describe data elements and their relationships. Also used specifically to refer to the part of SQL used for data definition.

DDLSw:  See Desktop DLSw.

DDM:  Distributed Data Management. A cross platform function using LU6.2 and APPC facilities to network processes on one machine with data on another. In effect, it’s a protocol for distributed file access. DDM is one of the base architectures for IBM’s distributed database and was implemented in September 1990 on the mainframe, having been available for many years prior on the AS/400, System 38 and System/38. Other platforms followed. Today, it is still a key component of DRDA in DB2. See also FTS1, DRDA.

DDN1:  Defense Data Network. MILNET and several other United States Department of Defense networks.

DDN2:  Document Distribution Node. Network node with storage, processing, and communications capabilities to attach and support workstations within a DIA network.

DDname:  Data Definition Name.

DDNS:  Dynamic DNS.

DDOS:  Distributed Denial of Service. Hacker technique of first secretly gaining remote access to a large number of Internet-attached computers, then triggering all of them to simultaneously flood a specified Web site with spurious traffic. The Web site is effectively shut down.

DDP:  Distributed Data Processing. Generic term for applications where the intelligence in the system is not located at a single point or in a single device. Though very popular in the late 1970s, the term has not been heard much since. Nonetheless, client/server is a DDP architecture.

DDR:  Dynamic Device Reconfiguration. z/OS facility for reconfiguring a broken device. Can be used dynamically, i.e., without stopping the program using the device, or shutting down the system.

DDS1:  Document Distribution Services. Component of DIA supporting distribution, requesting, store and forward, and delivery in a document distribution system. DDS can function in a store and forward mode – that is the originator and receiver do not need to be connected when the transmission of information is initiated.

DDS2:  Database Definition Specification. Utility on the iSeries 400 for the development of display, print, and database definition files. Offers similar facilities to SQL.

DDS3:  Data Definition Statement.

DDS4:  Distributed Data Services. See StorePlace.

DDV:  Direct Document View. Obsolete 8100/DOSF feature enabling users to view a DISOSS document without first having to retrieve it onto the 8100 system.

DEA:  Data Encryption Algorithm. Public standard for data encryption. Used in IBM’s Integrated Cryptographic Feature.

Dead Gateway Detection:  An AIX networking function. IP multi-path routing with multiple gateways where a failure of a gateway is detected and data is automatically routed through alternate gateways.

Deadlock:  A conflict in resource locking order between two requestors both wishing to update the same resources. The simplest example is two programs both wishing to lock the same rows in the same two tables at the same time. One locks the first table first and the other locks the second table first. They will both wait forever for the other to complete. The OS/400 Integrated File System, for example, has a deadlock detection feature that helps diagnose applications with conflicting lock ordering.

Debit-Credit:  A transaction processing benchmark for OLTP systems. Developed by the Bank of America and has become a de facto standard, although IBM shows little enthusiasm for it, preferring its own RAMP-C measure. Unlike RAMP-C, Debit-Credit is a public standard, but one which vendors treat with scant respect, and comparing one set of Debit-Credit results with another is by no means straightforward. Debit-credit is now largely out of fashion, replaced by the TPC’s benchmarks. See ET-1, TPC, TP-1.

Debug:  The human problem determination process for software. Literally, to remove bugs.

Debugger:  A tool for debugging.

Debug Tool:  Debugger. An optional feature of many IBM compilers, such as IBM PL/I for z/OS and z/VM where it is part of the Full-Function Feature.

DEC:  Digital Equipment Corporation. Computer manufacturer founded in August 1957 by Kenneth Olsen. During the eighties, DEC was a large pain in IBM’s corporate derrière – its VAX line sold very well into IBM accounts, much to the jolly giant’s chagrin. By the 1990s, DEC was in just about as much trouble as IBM. In January 1998 DEC was sold to Compaq for $9.6 billion – the largest acquisition in the history of the computer industry.

DECnet:  DEC’s family of network products based around Ethernet.

Decode:  Translating an encoded object back to its original form.

Decryption:  Converting cipher text to plain text.

DEDALE:  Expert system for analog circuit diagnosis. IBM research project.

DEDB:  Data Entry DataBase.

Dedicated Token Ring:  32Mbps Full Duplex Token Ring technology on new adapters and on certain Token Ring switches. See also Token Ring Network.

Deep Blue:  The 1.4 tonne, chess playing IBM RS/6000 SP that finally beat chess grand master Gary Kasparov in New York in May 1997. IBM’s RS/6000 SP, with its 32 P2S3 microprocessors and 512 dedicated chess processors, with the ability to assess 200 million possible moves per second, beat Kasparov in a six game contest. IBM considers the RS/6000 SP as having application for pharmaceutical drug development, molecular dynamics, and financial risk assessment.

Deep Thought:  An IBM chess playing machine which was the first artificial intelligence machine to be granted Grand Master status in the chess world in 1983. It was the precursor to Deep Blue, the RS/6000 SP which eventually beat Grand Master Gary Kasparov in May 1997.

De facto:  Actual, not rightful according to the dictionary. Used to describe standards such as SNA, the mainframe architecture, and the PC, which dominate the market, usually to the detriment of the rightful (de jure) standards such as OSI.

Default group:  The group specified in the RACF user profile that becomes the current connect group unless another group is specified at logon.

Defragmentation:  The use of a software utility to improve access and retrieval time by rewriting fragmented data to contiguous sectors of a computer storage medium.

Delegation:  Giving groups or users the authority to use some security administrator functions of RACF.

Delivery Manager:  IBM SystemView product (also known as SAA Delivery Manager) announced September 1990. Enables software and data to be delivered to networked OS/2 workstations from an MVS or VM host, and between hosts. Can be driven centrally or remotely. AConnS is a prerequisite. January 1992, CICS and PC-DOS support added. Withdrawn December 1993.

Delta disk:  The virtual disk in VM that holds temporary program fixes.

DEN:  Directory Enable Network. See DMTF.

Dependent LU:  See DLU.

Dependent workstation:  Old IBMspeak for MFI workstation (dumb terminals). Preferred to MFI in the UK, where MFI is the name of a large chain of stores purveying low-price furniture.

DEQ:  See Dequeue.

Dequeue:  The removal of a named entry from an z/OS system resource queue in which it has been enqueued (see Enqueue). Also known as DEQ.

DES:  Data Encryption Standard. Originally developed by IBM in 1971, now an NIST standard first published in 1977. A block cipher that encrypts 64 bits at a time using a symmetric algorithm. Supported by IBM in z/VM passwords, the Common Cryptographic Architecture, RACF, and ICRF.

Design Center for e-transaction Processing:  Project teams pulled together from across IBM to help large companies build comprehensive e-business environments with IBM servers, software and services, and integrate their business processes with that new environment they just built. Began July 1999, with a dedicated facility in Poughkeepsie, New York in March 2000, a second and third soon after in Montpellier, France and Makuhari, Japan.

DeskStar:  Version of the UltraStar disk drive for use in desktop PCs.

Desktop DLSw:  A scheme whereby SNA/APPN traffic is encapsulated within TCP/IP packets right at its source (e.g., PC/workstation) even before it reaches the LAN. Only justifiable in dial-in scenarios for mobile-users.

DET:  Device Entry Table.

Developer Network:  A service for people building applications around Lotus products. Includes a technical forum, expanded knowledge base, tools and newsletter.

Developmate:  Business modeling and prototyping tool announced along with AD/Cycle in September 1989 to run in MVS+OS/2 environments. Defines a business’s processes and data in terms of entity-relationship models stored in a Repository. An analyst’s, not a programmer’s tool. Withdrawn July 1994.

Device driver:  The code needed by a computer to allow it to interface with an attached I/O device.

Device Level Select:  Feature first introduced on 3380D/E that lets any two devices in a two path string read or write data simultaneously. DLS Enhanced was introduced with the 3380J/K, expanding DLS to four data paths. See also Dual porting.

Device pool:  A group of similar devices that can be shared by a group of users.

DFC:  Data Flow Control. SNA layer (number 5) defining protocols for managing LU-LU data flows.

DFDS:  Data Facility Device Support. Venerable software product for supporting various devices – mainly DASD. Withdrawn December 1991.

DFDSM:  Data Facility Distributed Storage Manager. Became ADSM then Tivoli Storage Manager.

DFDSS:  Data Facility DataSet Services. Renamed DFSMSdss.

DFEF:  Data Facility Extended Function. MVS software now integrated into DFSMSdfp.

DFHSM:  Data Facility Hierarchical Storage Manager. Renamed DFSMShsm.

DFP1:  Data Facility Product. Renamed DFSMSdfp.

DFP2:  Dynamic Feedback Protocol.

DFS:  Distributed File System. Runs on DCE2 to provide a single, shared file space for all authorized users from all possible locations across different platforms. Supports replication, providing high availability by placing multiple geographically-dispersed copies of files and applications. File names and paths are location-independent so that files can be relocated without renaming. Caching stores the most commonly used files close to the workstation that is using them. Available for AIX. Supported as Distributed File Service (DFS/SMB) in z/OS.

DFSMS:  Data Facility Storage Management Subsystem. An element of z/OS and also available for z/VM, as DFSMS/VM. But it began life February 15, 1988, as an IBM term for its then-new approach to data management: the notion that you will no longer need armies of systems programmers and data administrators to look after your data – you simply tell the system about the storage, backup, performance and other requirements of the data, and the system does the rest for you. Then some bright boy in IBM mainframe software management realized that the company could save a bundle of money by packaging related software together, thereby avoiding the need to test every possible combination of supported version/release of each product together. He named his guinea pig DFSMS/MVS and it was announced May 19, 1992. It combined and replaced MVS/DFP1, DFHSM, DFDSS and TLCS, as they had been previously known, renaming them DFSMSdfp, DFSMShsm, DFSMSdss and DFSMSrmm. The bundling concept worked so well that it was tried on a much grander scale: OS/390, a bundling of MVS/ESA and many systems software products. z/OS continued the tradition, with DFSMS as a component.

DFSMS/VM:  Data Facility Storage Management Subsystem/VM. z/VM version of z/OS DFSMS, providing SMS1 space management for SFS and mini-disk files, including migration and management classes. ISMF is also included, along with 3495 tape library support. But, when first announced in October 1989, there was lots of marketing hype but not a lot of product substance. It was little more than a utility with an ISMF interface for speeding DASD conversions, and managing mini-disks. Things got better by mid 1992 with space management for SFS files, FBA support and 9348 tape support under VM/ESA. Today it is a component of z/VM.

DFSMSdfp:  DFSMS Data Facility Product. A component of z/OS DFSMS that provides functions for storage, data, program, and device management, in conjunction with distributed data access. Enables the definition of the services to be assigned to new datasets. Handles catalog management and access methods. Formerly a separate product known as DFP.

DFSMSdss:  DFSMS DataSet Services. An optional, separately priced feature of z/OS DFSMS that handles device migration, copy, space management, and dump/restore. It also converts existing data between non-SMS and SMS volumes, and provides an interface for storage administrators (ISMF). Formerly a separate product known as DFDSS (Data Facility DataSet Services).

DFSMShsm:  DFSMS Hierarchical Storage Manager. An optional, separately priced feature of z/OS DFSMS known mainly for its uncanny ability to migrate your datasets to tape just before you next need to use them. In fact, hsm is a sophisticated automated system for both backup and hierarchical storage management. It includes an ISPF interface for end users who wish to migrate, recall, backup or recover individual datasets, or to override the default migration and/or backup parameters. The hierarchy being referred to is flexible, but most installations define so that Level 0 is standard disk storage, Level 1 is compressed disk storage and Level 2 is tape. Datasets have to be recalled to Level 0 before they can actually be read or written. hsm also includes a disaster recovery feature known as ABARS. Originally introduced in the early 1980s as a separate product known simply as HSM, then later renamed DFHSM (Data Facility Hierarchical Storage Manager), before becoming the DFSMShsm component of DFSMS/MVS (now just DFSMS) in May 1992.

DFSMSrmm:  DFSMS Removable Media Manager. Initially, as TLCS, it was a rather unpopular tape library management system. A major revamping and inclusion in DFSMS/MVS (now just DFSMS, a component of z/OS) when it was announced in May 1992 saw customers flocking to it, most from supposedly enternched non-IBM tape library management products. Its goal was to integrate the system managed storage principles of DFSMS into all removable media, most notably tape and optical. Manages shelves and media storage as well as the media volumes themselves. An optional, separately priced feature of z/OS DFSMS.

DFSORT:  Data Facility Sort. An optional, separately priced feature of z/OS, it began its life as the venerable Sort/Merge of the original System/360 OS/360 and DOS/360 operating systems, back in the days when software was free and hardware was what you paid for. It had a reputation for sluggishness, but it was hard to compete with free. Nonetheless, given how much sorting is involved in business batch data processing, competitive sort/merge packages were one of the first software products to hit the market. At one time, SyncSort had over 70% of the market. Computer Associates was founded with an acquired sort/merge package as its first product. Until the 1990s, DFSORT was dogged with performance problems, but started to shake them as each new release bested SyncSort in benchmarks and in-house tests. SyncSort, of course, would then come out with a new release that beat DFSORT. Beyond sorting, DFSORT has become a major utility in its own right, especially with the addition of ICETOOL. See also DFSORT/VSE, DFSORT/CMS.

DFSORT/CMS:  Data Facility Sort/Conversational Monitor System. The z/VM implementation of DFSORT. Announced February 1988, but no new releases announced since Version 2 in September 1990. Still marketed and still supported. Replaced DOS/VS-VM/SP Sort/Merge.

DFSORT/VSE:  Data Facility Sort/VSE. Announced September 1994 as Version 3, replacing Version 2 of DOS/VS-VM/SP Sort/Merge, DFSORT/VSE has evolved into a close match to the z/OS implementation of DFSORT.

DFT:  Distributed Function Terminal. A mode of operation used in a 3274/3174 controller where the device LU logic is maintained in the (intelligent) terminal downstream of the controller. In this mode the terminal can manage more than one session with the host. The controller has a much more passive role when DFT is in use. DFT allows terminals to communicate using the LU6.2 protocols, and is likely to replace the CUT protocol in the long term. Used by the 3290 and IBM PC when attached to a 3274 in DFT mode.

DFU:  Data File Utility. iSeries 400 utility for developing simple data maintenance systems (query, file maintenance, etc). A System/36 leftover that is now part of ADTS.

DFW:  See DASD Fast Write.

DH:  See Diffie-Hellman algorithm.

DHCF:  Distributed Host Command Facility. Feature supporting SNA network management for System/3x, AS/400 and iSeries 400. System/36 DHCF provides access to System/36 applications from 3270 terminals on a mainframe host.

DHCP:  Dynamic Host Configuration Protocol. A protocol defined by the IETF for dynamically assigning (on demand) IP addresses to computers in a network.

Dhrystone:  A measure of machine performance for compute-intensive applications. Roughly, 1757 Dhrystones/second is 1 MIPS.

DHTML:  Dynamic HTML. A synergistic combination of HTML, style sheets, and JavaScripts that exploit the newest capabilities in Version 4 (and above) Web browsers, to allow the development of animated and interactive Web pages.

DIA:  Document Interchange (Interface) Architecture. The set of standards and rules (part of SAA CCS1) for sending documents around IBM computer systems – the electronic envelope. DIA is implemented as a set of SNA communications programs – IBM would like all DIA to use LU6.2, but for compatibility LU2 is also supported.

DIAL-IBM:  Direct Information and Assistance Link to IBM. Telephone link to an IBM database to enable IBM to shift more iron. Defunct.

Dialog Manager1:  Application announced May 1989 for creating CUA1 compliant systems on the PS/2. Obsolete.

Dialog Manager2:  Term often used to refer to ISPF, as opposed to its PDF1 component.

Dial-up:  See Switched line.

Dial-up line:  See Switched line.

Dictionary Model Transformer:  See DMT.

DIDOCS:  Device Independent Display Operator Console.

DIF1:  Document Interchange Facility. IBM program which provided a link between DCF/DLF and DOSF/8100 terminals. Ran on mainframes and the 8100. Obsolete.

DIF2:  Data Interchange Format. A standard format (developed by Software Arts in the US) for interchange of ASCII data. Became a de facto standard for interchange of data between PCs – most spreadsheet and several database packages can read DIF files. Obsolete.

DIF3:  Display Information Facility. Rudimentary application generator and query system on the System/38. Obsolete.

Diffie-Hellman algorithm:  A public key algorithm used for secure key exchange.

DiffServ:  Differentiated Services. A Quality of Service (QoS) function of OS/400.

Digital certificate:  In the SET architecture, a digital document containing the certificate owner’s public key and a digital signature. The certificate authenticates the identity of the owner because it is issued by a certification authority.

Digital Certificate Manager:  OS/400 software with SSL that supports X.509 certificates and Global Server Certificates for HTTP, LDAP, telnet and client access servers, DDM, DRDA, Management Central and Operations Navigator.

Digital envelope:  In the SET architecture, this is a unit of encrypted data and the encryption key.

Digital Equipment Corporation:  See DEC.

Digital Library:  Replaced by Content Manager for Multiplatforms.

Digital Research:  Microcomputer software company which failed to build on the success of its CP/M, the first successful microcomputer operating system. The story, still shrouded in controversy to this day, is that the DR bigwigs were out when IBM called in the early 1980s to ask DR to develop an operating system for IBM’s new PC. Unused to being treated with such scant respect, the IBM executives stomped off in a huff to Microsoft, where, ten years later they found they were treated with even less respect. In 1991, DR was taken over by Novell.

Digital signature:  In the SET architecture, a digital string used to authenticate the message it is attached to, verify that it has not been tampered and, optionally, identify the sender.

DIM:  Data In Memory. The principle of always holding as much data as possible in the main memory of the computer – or at least as high up the data storage hierarchy as possible. When the idea was first floated by IBM in the late 1980s, many a Technical Support manager dreamed of buying enough memory to store his primary DB2 databases totally in memory. And DIM proved itself quickly in Hiperbatch and CICS with customers reporting throughput improvements of over 60%. See also Memory-based computing.

Dinosaur1:  Unflattering terminology for old minicomputers and mainframes. Many mainframe enthusiasts have embraced the term, pointing out that dinosaurs survived for 150 million years. There is even a Dinos Web ring linking Internet sites covering mainframe topics.

Dinosaur2:  IBMspeak for a conservative user with a closed mind. See Zipperhead.

Dinosaur mating:  A derogatory industry term to describe the process of big iron mergers in the 1960s and 1970s. In the 1960s the main players in the computer industry were IBM and the Seven Dwarves, the Dwarves being Burroughs, Control Data, General Electric, Honeywell, NCR, RCA, and Univac. After the loss of GE and RCA the Seven Dwarves metamorphosed into the BUNCH (Burroughs, Univac, NCR, Control Data, and Honeywell). Further mergers and sell outs left the marketplace unrecognizable. See Dinosaur1, BUNCH, Seven Dwarves.

DIOF:  Display Input/Output Facility. Full-screen (3270) I/O facility for z/VM. Also known as IOS3270.

DIP:  Document Image Processing. Generic term for systems and equipment which create and store images, usually of correspondence and documents. See 389x, 3117-9, ImagEdit, ImagePlus.

Directed command:  A RACF command specifying AT or ONLYAT, issued from a user ID on an RRSF node.

Director:  IBM Director with UM Services. See NetFinity.

Directory Audit:  An AIX directory server security audit log facility that includes a time stamp and BindDN in each log record. Audit plug-in support allows any application, such as a centralized audit package, to receive the audit data and filter to incorporate with other audit information.

Directory-based Resolvers:  Name resolver routines have been enhanced to include resolving hostnames through an LDAP server

Directory server:  APPN network node which serves as a repository for information about where things are in a network. Directory servers help to focus APPN network searches and limit the number of network-wide (broadcast) searches.

Directory services:  Generic name for the network control element which contains a directory of the names and addresses of all the network elements and the translation tables to turn a partial address (e.g., a name) into a full address. Within traditional SNA, directory services are provided by VTAM in the SSCP; in APPN and more distributed network architectures, the directory services may be distributed around the network in directory servers. See also X.500.

Direct Route/2:  OS/2 voice/data application which intercepts incoming telephone calls, and brings the caller’s details up on the operator’s screen by the first ring of the telephone. The system was developed by IBM in conjunction with a US electricity company. Usable only with Nortel exchanges. Not a terribly important product in its day – CallPath was the key voice/data offering. Obsolete. See also DirectTalk.

DirectTalk:  CallPath and Direct Route/2 facility announced July 1991 which runs on RS/6000 and PS/2, and enables the user to access spoken information from a standard telephone. The message sent to the caller is either pre-recorded or created by speech synthesis. Long-term replacement for the 9270/4.

Direct Window Access:  Beginning with AIX 5L, OpenGL on POWER GXT4000P and GXT6000P graphics adapters supports 64-bit Direct Window Access (DWA). Intended to boost performance for 64-bit OpenGL applications by allowing them to render using the OpenGL protocol directly, rather than going through the Xserver and GLX Extension.

DirMaint:  Directory Maintenance. A z/VM CMS subsystem used to maintain the VM directory. User IDs and their private mini-disk can be defined with DirMaint commands.

DIS1:  Direct Information Services. On-line catalog of all IBM products and services. Available through IBM’s INS service. Defunct.

DIS2:  Data Interpretation System. Workstation tool (data access, analysis, presentation, etc of EIS/DSS-type data), based on the Metaphor user interface. From April 1993 DIS was sold only under Metaphor’s name, not IBM’s. And IBM stopped marketing it altogether in October 1994. Metaphor stopped marketing the product at some point after that.

Disaster Recovery Manager:  An optional feature of ADSM. Replaced by Tivoli Disaster Recovery Manager.

Disaster Recovery Plan:  A documented set of procedures to be used in the event of a major computer outage.

Discontinuous Binary:  A date format used in some mainframe systems.

Discount:  For years it was beneath IBM’s dignity to join in the hurly-burly of the marketplace with anything quite as vulgar as discounts. These days, times are tough, things are different, and the IBM salesman slugs it out with the rest of them – see ASGO, DSLO, GIO, HESC, Market basket, OSTA, SCO2, Special bid, TSP, VLA, VPA, VWA.

Discovery:  The ability of software to determine the existence and identity of hardware or software, typically on a network, but arguably also on a workstation in the way that Windows operating systems fill the screen with those annoying Found New Hardware dialog boxes.

Discovery Server:  Lotus Discovery Server. Extracts, analyzes and categorizes structured and unstructured information, attempting to determine the relationship between the content, people, topics and user activity within an organization. It will automatically generate and maintain a Knowledge Map (K-map) to display relevant content categories. Originally part of the Lotus Knowledge Discovery System, which also includes K-station. Version 1.1, announced October 2001, became a stand-alone product.

Discrete profile:  A resource profile that provides RACF protection for a single resource.

Discretionary access control:  The resource owner defines who can access the resource.

Disk array:  Generic term for a disk drive made up of a large number of small platters and heads. Compared with traditional DASD design, the technology offers the potential for better performance (the smaller disks spin faster, and the head has less distance to travel), a high degree of fault tolerance, and the ability to use techniques such as disk striping (although, the performance improvement is small in practice). The first disk array that IBM produced was part of the Super Computing Systems Extensions (see SCSE, 9570); there are now RAID disks for all IBM platforms, and IBM is committed to a strategy of using arrays as the basis of all its disk products. The technique is also known by the generic term Redundant Arrays of Inexpensive Disks (see RAID for further details). See also 9337, Iceberg, RAMAC2.

Disk striping:  Technique for very high-speed data access from multi-platter DASD. Data is stored one bit on each platter, and all data bits are accessed in parallel (a bit like early drums). See also File striping.

DISOSS:  DIStributed Office Support System. At one time the principal IBM mainframe system for office automation. Was the first strategic implementation of DIA/DCA on a mainframe. Runs on z/OS under CICS. Although it was strategic for some time, DISOSS is now just another bit of system software which provides three functions for connecting incompatible systems – e-mail, text database, protocol/format translation. Obsolete.

DISOSS/PS:  DISOSS Professional System. Obsolete.

Display PostScript:  Screen writing version of Adobe’s PostScript language. Originally a feature of the AIXwindows user interface, it was announced as a separate product July 1994: IBM AIXwindows Display PostScript (AIX DPS). Withdrawn July 1997 after support ended December 1996 with the suggestion that Adobe might have a replacement.

Display Technologies:  Joint venture formed between Toshiba and IBM in 1989 to build large liquid-crystal color displays. The partnership ended in August 2001, each company absorbing portions of DTI.

DisplayWrite:  Family of IBM word processor software originally for the PC, PS/2, System/3x, and mainframe (including DPPX/370). The OS/2 and PC-DOS versions were withdrawn in May 1995, although support had already ended in December 1992. Support ended for the VSE/ESA version March 2002. The z/OS and z/VM versions of DisplayWrite/370 are still available.

DisplayWrite Composer:  Text layout tool designed for use with DisplayWrite under OS/2 and, since October 1990, DOS. Withdrawn September 1992.

Displaywriter:  Defunct IBM stand-alone word processor and desktop micro. The announcement of DisplayWrite software for the PC, System/36, and mainframe was the kiss of death for the hardware, and the apotheosis of the software.

Distributed:  Distributed systems are those that run on a collection of separate computers, with each computer performing part of the overall workload. See also DDP.

Distributed Debugger:  A GUI for debugging programs, found on many platforms, for many programming languages, in many IBM products. Including C/C++ Productivity Tools, where it runs on Windows NT/2000/XP workstations, working with IBM Debug Tool to source level debug z/OS C and C++ programs running in TSO, batch, CICS, IMS, DB2, Unix System Services and WebSphere. It can even debug multi-threaded and multi-process C/C++ applications. Distributed Debugger is also a part of the CODE component of WebSphere Development Tools for iSeries. It can also be found in VisualAge for Java Enterprise Edition. And WebSphere Application Server Advanced Edition. There is also an AIX version that runs on Windows NT/2000/XP workstations.

Distributed File System:  See DFS.

Distributed Key Management System:  Security management software from IBM that provides central management of encryption keys.

Distributed Security Manager:  Family of security administration programs first mooted in September 1994. Available February 1996, initially on z/OS with an OS/2 workstation GUI. An AIX version was previewed October 1995. In 1997, both products were withdrawn and absorbed by Tivoli, eventually becoming part of Tivoli SecureWay Security Manager.

Distributed Unit Of Work:  A distributed unit of work is a group of SQL statements, accessing data that may be situated at multiple physical locations, which would need to be rolled back as a group if any single statement in the group could not be executed. Each SQL request in the DUOW can access only one system. The DUOW is the basic recovery unit where SQL originated on one machine accesses a database on a number of other machines. Supported in DB2 with effect from March 1993. See also Remote Unit of Work.

DITTO:  Data Interfile Transfer, Testing and Operations. Venerable VSE/ESA, z/VM and z/OS utility for tape, card, and disk devices, and OAM objects. Allows the user to browse, copy, print, update, and create files. Runs interactively, in batch and callable from REXX. Still alive and well, and currently known as DITTO/ESA for all three platforms.

DIU:  Document/Distribution Interchange Unit. The unit of interchange within the DIA architecture.

DIV:  Data In Virtual. A z/OS technique for holding specific types of data, such as VSAM linear datasets, permanently in virtual memory. See also DIM, Memory-based computing.

DIVE:  Direct Interactive Video Extension. A set of APIs within OS/2.

DKMS:  See Distributed Key Management System.

DL/I:  Data Language/I. The I is the Roman numeral one. The data manipulation language within IMS DB. DL/I is also the product name for IBM’s VSE/ESA implementation of IMS DB.

DL/I transparency:  The ability to process relational data through DL/I calls in an application. DL/I transparency enables existing applications to be run using the new database. cf. SQL transparency.

DLC:  Data Link Control. The rules (protocol) used by nodes on a network connection (data link) to communicate with each other. See also GDLC.

DLF:  Document Library Facility. Library facility for storing text. DLF includes security, user types etc. Input data can be from user systems, DOSF, ATMS III, DCF, etc. Text is stored in VSAM files. Runs in batch on z/OS and VSE/ESA. It does not run directly in z/VM, but can run on a z/OS or VSE/ESA guest, handling text edited in CMS1.

DLL:  See Dynamic Link Library.

DLPI:  Data Link Protocol Interface.

DLR:  DOS LAN Requester. Component of the OS/2 LAN Server which provides LAN connectivity to PC-DOS clients.

DLRPL:  Dump/Load/Restart Parameter List.

DLS1:  Document/DISOSS Library Services. Component of DIA supporting the storage and retrieval of information. Replaced by DLS-E1.

DLS2:  See Device Level Select.

DLS3:  Data Link Switching (aka DLSw). Technique introduced in the 6611 router early 1993 for transporting SNA, APPN, and NetBIOS traffic through a multiprotocol network as efficiently as possible without affecting the end-system applications. Works by encapsulating data within a TCP/IP datagram. Supported in the 6611, 2210, and many non-IBM products, and more or less an industry standard.

DLS-E1:  Document/DISOSS Library Services – Enhanced. Program offering which provided some add-on features to DLS1 (more tools, wider access, more administrative services). Withdrawn June 1998.

DLS-E2:  Device Level Selection – Enhanced, aka DLSE. Provides four independent and simultaneous data transfer paths to a single mainframe DASD string.

DLSw:  Data Link Switching. See DLS3.

DLU:  Dependent Logical Unit. SNA logical units which require the presence of an SSCP – LU0, LU1, LU2, LU3. DLUs are the most commonly used type of LU in legacy networks, and some way of handling them will be necessary when the world switches from Subarea SNA to APPN.

DLUS/DLUR:  Dependent LU Server/Requestor. A technique for allowing traditional SNA traffic (including 3270) to be routed in APPN, and to share some of the advantages of APPN – dynamic multi-hop routing and resource allocation, and simplified host configuration. Transparent to dependent devices and applications.

DM/VSE:  Document Management VSE. A little known product supporting document management in the VSE environment. Replaced by VSE Office Offering May 1990.

DM1:  Distribution Management. The name for the combination of the DSX host and DSNX node products providing host management for the distribution of software, updates, listings etc to remote System/3x nodes. Now part of Tivoli NetView Distribution Manager.

DM2:  Database Manager. The relational DBMS within OS/2 Extended Edition. Replaced by DB2 Universal Database for OS/2.

DM3:  See Dialog Manager2.

DMA:  Direct Memory Access. Generic term for a hardware feature for transferring data between memory and I/O units without processor intervention.

DMAPI:  Data Management Application Programming.

DME:  Distributed Management Environment. The part of the OSF specification which provides the architecture for vendor-neutral distributed systems. Includes AIX’s System Resource Controller, and IBM database technology.

DMI:  Desktop Management Interface. A protocol-independent set of APIs produced by the Desktop Management Task Force (DMTF).

DMIG:  Data Management Interfaces Group. Group of vendors – including IBM, HP, Transarc, Unisys – set up mid 1993 to define and promote specifications for Unix systems administration and storage management technologies. Disbanded.

DML:  Data Manipulation Language. The part of SQL used for data manipulation.

DMM:  Tivoli Data Message Manager. See Tivoli Data Exchange.

DMS/CMS:  Display Management System/CMS. Old and much-loved z/VM system for generating screens. Still available.

DMS1:  Development Management System. Defunct 8100/DPPX and mainframe application development system. Not well-loved and was replaced by CSP – which nobody seems to like very much either.

DMS2:  Delegated Management Services.

DMT:  Dictionary Model Transformer. Product for transferring information from the IMS1 Data Dictionary to Repository Manager/MVS. Defunct.

DMTF:  Desktop Management Task Force, Inc. Huge group of vendors and educational institutes worldwide, which is developing management standards for distributed desktop, network, enterprise and Internet environments. Board members include IBM, Compaq, HP, 3Com, BMC, Cisco, Dell, Intel, Microsoft, NEC, Novell, Sun and Symantec. Standards include the Common Information Model (CIM), Desktop Management Interface (DMI), Directory Enabled Network (DEN), Web-Based Enterprise Management (WBEM), Alert Standard Format (ASF).

DNA1:  Digital Network Architecture. DEC’s answer to SNA. Comprises all of DEC’s networking products – DECnet, DECnet/SNA Gateway, communications servers, etc.

DNA2:  Microsoft’s Distributed iNternet Architecture, announced in 1997. The acronym was contrived to match human DNA. DNA 2000 announced in 1999.

DNA 2000:  A revised version of DNA2, announced in 1999.

DNS:  Domain Name System. The distributed database system (directory) used to map domain names to IP addresses.

DOA:  Dead on arrival. Popularized by IBM’s early ThinkPads with their high initial failure rate out of the box.

Doctor DOS:  Another name for DR-DOS.

Document Object Model:  See DOM.

Document Search/400:  Full text retrieval system for the AS/400. Designed to work with ImagePlus and OfficeVision. Supports WAF. Obsolete.

DOLS:  Domino Offline Services.

DOM:  Document Object Model. An object hierarchy used by DHTML scripts and supported by HTML 4.0.

Domain1:  An SNA domain is the set of resources owned by a host SSCP, including the PU1s, LUs, links, link stations, and all the bits and pieces that the SSCP can control. It is assigned by a system programmer.

Domain2:  A group of servers in an OS/2 LAN Server network.

Dominion Semiconductor:  An equally-owned, joint venture between IBM and Toshiba that aimed to produce advanced microchips for computers and other products. The Dominion plant in Manassas, Virginia started operations in September 1997 with mass production of 64-megabit DRAMs. Toshiba bought IBM’s 50% share in December 2000.

Domino:  Web server technology from Lotus (June 1996), which allows browsers to interact with Notes and access Notes databases. An important milestone in groupware/intranet integration, Domino quickly took over the groupware server role from Notes, which has effectively been relegated to a client system. Products include Domino Application Server Domino Application Studio Domino Designer Domino Enterprise Server Domino Extended Search Domino Global Workbench Domino Mail Server Domino Offline Services Domino Workflow Domino.Doc

Domino.Action:  Intranet creation and management tool, from Lotus, powered by the Domino Server. Includes the SiteCreator and Domino.Applications modules. The modules are template-based software for the creation of customizable homepages, discussion databases, whitepaper databases, FAQs, etc. Obsolete.

Domino Designer:  A Lotus integrated development environment for Domino applications.

Domino Everyplace:  A family of products that provides access to mobile devices, such as PDAs, cell phones, pagers. Includes Domino Everyplace Access, Domino Everyplace Enterprise and Domino Everyplace SMS.

Domino Go Webserver:  Lotus Domino Go Webserver for OS/390. Web security and e-commerce software for z/OS. Announced October 1997.

DOR:  Data Owning Region in a CICS environment.

Dormant:  Under z/VM, a dormant state occurs when the active pages of a virtual machine have been paged out.

DOS/VS COBOL:  As the name implies, a COBOL compiler originally released in the 1970s, in the days of DOS/VS. Replaced March 1997 by IBM COBOL for VSE and Language Environment (LE) for VSE.

DOS1:  Historically, DOS/360 was developed in a hurry for smaller System/360 mainframes after OS/360 developers discovered that they had created a monster too large for the low-end models. DOS/360 became DOS/VS, DOS/VSE then VSE/ESA, as it remains today. In the early 1980s, a simplified, though limited, version of DOS/VSE was known as SSX/VSE, which prompted the reference to VSE, and saw the dropping of DOS, speeded, no doubt, by the other DOS, from Microsoft. VSE/ESA is still alive and well today, despite several near-death experiences over the years. See also VSE1.

DOS2:  Generic term for PC-DOS, MS-DOS, and Novell-DOS (DR-DOS).

DOS3:  Denial of Service. See DDOS.

DOS box:  Facility of early OS/2 (also known as the DOS compatibility box) enabling users to run PC-DOS as an application under OS/2.

DOSF:  Distributed Office Support Facility. Defunct 8100/DPCX software which provides shared facility word processing/office automation (OA) system, with mainframe communications capability. At one time DOSF with DISOSS was going to see IBM OA users into the 21st century (it didn’t!!).

Dotted decimal notation:  The method of representing an IP address. The 4 bytes of the address are written as four decimal numbers separated by dots, e.g.,

Double-Byte Character Set:  See DBCS.

Down and out:  Once popular name for a DP manager who downsizes to a smaller machine and then outsources his information systems to a facilities management company, thereby saving his employer money but destroying his career in the process. Down and outs can often be spotted on park benches and at industry conferences, muttering about the relative price/performance of mainframes and workstations.

Download:  The transfer of data from a computer to a connected device, such as a personal computer or workstation. cf. upload.

Downsizing:  The philosophy of moving a computing task off a big machine and onto a little one (e.g., from a mainframe to an iSeries 400, Unix or Windows environment). The benefit is that processor cycles are apparently cheaper on smaller machines; the drawback is that you almost inevitably reduce data integrity, security, database access, and all the good things that mainframes and professional DP do so well. Admittedly, the rest of the world has made some efforts to catch up over the years. See also Re-hosting.

Downstream:  The direction of data flow from the host to the user. Downstream can provide an indication of the location of devices and lines.

Downstream PU:  A remote SNA node supported at the data center by an SNA gateway of some sort. Mainly used to refer to LAN-attached devices supported by SNA-LAN Gateways (e.g., NetWare for SAA).

DPA1:  Document Printing Application. An OSI standard which allows electronic documents to be sent to shared dispersed printers in the distributed open systems environment.

DPA2:  Dynamic Paging Area.

dpAM:  DP Accounting Manager. Software which collects chargeback data into an Enterprise Performance Data Manager/MVS database. Withdrawn December 1997.

DPCX:  Distributed Processing Control eXecutive. Defunct 8100 operating system for high-performance interactive processing and support of text processing (DOSF); a hangover from the 3790. Based on highly centralized concepts, largely incompatible with, and even more obsolescent than DPPX.

DPD:  Data Processing Division. Many years ago, DPD was the part of IBM responsible for marketing and supporting IBM mainframe systems and certain other products (e.g., 8100). DPD, OPD (Office Products Division), and GSD (General Systems Division) each had responsibility for product development, and this split contributed to IBM’s overlapping and incompatible product range for which SAA was to be the panacea.

DPL:  Distributed Program Link. CICS facility which simplifies the creation of distributed applications among CICS systems. Allows a CICS client program to call a CICS server program in another CICS region or system. Can also be used instead of, or to reduce the use of, MRO/ISC1.

DPMI:  DOS Protected Mode Interface. A technique used in MS-DOS to access more memory than the 640KB it was originally designed around.

DPN:  Destination Program Name.

DPPX:  Distributed Processing Programming eXecutive. 8100 operating system optimized for general purpose transaction processing. Although the 8100 was long gone, DPPX/370 was not withdrawn until June 1997.

DPPX/370:  Version of the DPPX operating system which ran on the 9370 and low-end ES/9000s (models 120-170). Not a terribly important product – just a way of squeezing the last drop out of the 8100 user base (Preserving customer investment in IBMspeak). It was still going in April 1992, when APPC was added. Finally withdrawn June 1997.

DPR:  Dynamic Path Reconnect. z/OS feature enabling data transfers to/from DASD to be completed on the first available path.

DPROP:  See Data Propagator.

DPS:  Distributed Presentation Services. Obsolete 8100/DPPX screen management product.

DRAM:  Dynamic Random Access Memory. A commonly-used memory chip technology that used capacitors to store electrical charges. Dynamic indicates that the capacitors eventually lose their charge, and must be regularly refreshed. See also SDRAM, SRAM.

DrawMaster:  Venerable line drawing package for VM1/APL/GDDM environments. Withdrawn April 1993.

DRDA:  Distributed Relational Database Architecture. The agglomeration of bits and pieces of communications supporting distributed databases in the IBM world announced July 1990. DRDA has since become an Open Group Technical Standard and there is widespread software support for DRDA in the vendor community. DRDA is the key enabler for the Information Warehouse. See also DDCS.

DR-DOS:  PC-DOS compatible microcomputer operating system from Digital Research. Never did very well against MS- and PC-DOS, despite being widely considered superior to the Microsoft-based DOS – it had better memory and disk management, and it usually worked out a bit cheaper. After Digital Research passed into the hands of Novell in 1991, DR-DOS received new impetus, particularly as a client in NetWare networks, and became Novell-DOS. But, all that changed in July 1996 when Caldera acquired it from Novell as the basis of a law suit against Microsoft. But, then again, it was a Windows world by then, anyway.

DRM1:  See Tivoli Disaster Recovery Manager.

DRM2:  Dynamic I/O Reconfiguration Management.

Drop:  IBM terminology for the cable in a wiring closet that runs from a faceplate to the distribution panel.

DRP:  See Disaster Recovery Plan.

DS:  Dictionary Services. Tool which would have transferred definitions from external libraries (load library, COBOL copy library) into the Repository Manager’s information model had the Repository Manager not bitten the dust.

DSA1:  Direct Serial Attach. Architectural feature in which the disk controller is part of the disk device, and is connected directly to a serial ESCON channel.

DSA2:  Digital Signature Algorithm.

DSAT/400:  Distributed Systems Administration Tools/400. AS/400 software (February 1992) which allows remote AS/400s to communicate with a central AS/400 running CSAT/400. Withdrawn December 1995.

DSB:  Dispatcher/Scheduler Block.

DSC:  DataStream Compatibility – e.g., 3270 DSC. Usually applied to terminals and printers of LU type 3, which allow 3270 conventional formatting capabilities compatible with those permitted under BSC protocols.

DSD:  Dedicated Servers for Domino.

DSECT:  Dummy control SECTion. An Assembler statement usually used to define a record layout, control block or other formatted area of memory. But, the trick is, it is not mapped to memory, allowing it to used repeatedly in an Assembler program for different areas of memory, or dynamically assigned to an area of memory by the program. The DSECT statement names the dummy control section, as well as indicating that the memory definitions that follow are in that dummy control section.

DSF:  Device Support Facility. See ICKDSF.

DSL/VS:  Dynamic Simulation Language. Mainframe package for simulating continuous systems describable by differential equations. Ran on VM/CMS and TSO in MVS. Announced April 1984 as a Program Offering with support ending June 1987.

DSL1:  See Dynamic SQL.

DSL2:  Digital Subscriber Line. Digital communication protocol which transforms twisted-pair copper (telephone) lines into high-speed data channels: initially 1.54Mbps but much more now. Genealogy derived from AT&T’s video-on-demand protocol. Often known as xDSL because of all the different variations. It competes well against ISDN, cable modem and even T1, but most of the connections are in the consumer market, for high speed Internet. The ADSL variation is especially well suited because it dedicates most of its bandwidth where it is needed: from the ISP to the customer.

DSLO:  Distributed System License Option. Discount for users buying multiple copies of IBM software. In exchange for the discount, the user agrees to distribute the software himself rather than letting IBM do it.

DSM1:  Distributed Storage Manager. See Tivoli Storage Manager.

DSM2:  Distributed Systems Management.

DSM3:  See Distributed Security Manager.

DSM4:  Data Services Manager. A function in Tivoli NetView for z/OS that provides VSAM services for data storage and retrieval.

DSMON:  See Data Security Monitor.

DSN:  Dataset name.

DSName:  Dataset name.

DSNX:  Distributed Systems Node Executive. Software which sits in a distributed system to support unmanned data distribution across a network – essential for effective distributed processing. The DSNX machine talks to a host machine running the DSX software which is used to distribute software, updates, etc. The combination of DSX and DSNX is known as DM. Now part of Tivoli NetView Distribution Manager.

DSOM:  Distributed System Object Model. An object-oriented architecture (vintage June 1993) developed from SOM. Provides a common mechanism (based on DCE2) for communicating between objects across a network. Obsolete.

DSORG:  Data Set Organization. The type of data set (file) being created or referenced if the data set is usually not cataloged; e.g. DSORG=PS or DSORG=PO (PO-Partitioned) (PS-Physical Sequential)

DSP:  Digital Signal Processors. Specialized processor chips used especially in modems, sound boards, and serial ports.

DSPT:  Display Station Pass Through. Facility on the iSeries 400 enabling workstations on one machine to log on to applications on another.

DSPU:  SNA DownStream Physical Unit. See Downstream PU.

DSR1:  DataSet Ready. DSR is sometimes seen on modems, as the label for a status light.

DSR2:  Dynamic Storage Reconfiguration.

DSS1:  Decision Support System. Generic name for a class of end-user tools – typically high level financial and market modeling tools – which allegedly help people to make decisions, by providing user-friendly tools for ad hoc query, data analysis, one-off report writing, information presentation, etc. More commonly, they enable people to postpone decisions by encouraging them to spend hours drawing graphs and diagrams on a workstation instead of actually making their minds up. IBM DSS offerings have included OfficeVision, APL and AS1. DSSs are often confused with EISs (Executive Information Systems) – see EIS2 for an explanation of the difference. See also PIM, ESS1.

DSS2:  Digital Signature Standard.

DSSSL:  Document Style Semantics and Specification Language. International Standard ISO 10179 (ISO1994), adopted at the beginning of 1995. It presents a framework for transforming a structurally marked up document into its final physical form. The standard is primarily targeted at document handling, but it can also define other layouts, such as those needed for use with databases.

DSU:  Distribution Services Unit. In effect the node in a SNADS network. A DSU may be an originator, recipient, or an intermediate store-and-forward node.

DSU/CSU:  Data Service Unit/Channel Service Unit. See 5821/2.

DSX:  Distributed Systems Executive. Venerable product providing central host library support, program dump, and batch data transmission among mid-range systems (8100, Series/1, and System/3x) connected in an SNA network. DSX on the host communicated with DSNX on a distributed node. The z/OS version of DSX was replaced by NetView Distribution Manager in May 1988 but the product lived on in the VSE environment until it was withdrawn in August 1993. The combination of DSX and DSNX is also known as DM. Now part of Tivoli NetView Distribution Manager.

DTB:  Dynamic Transaction Backout.

DTD:  Document Type Definition. This is a specific markup language, written using SGML.

DTE:  Data Terminal Equipment. Term describing the subscriber equipment attached to a ITU-T network (usually packet switched). The DTE serves as a data source, data link, or both, and provides the protocol support for the link. A 3745 is a typical piece of DTE.

DTI:  Display Technologies Inc. See Display Technologies.

DTL:  Dialog Tag Language. Language for developing dialog panels, command tables, and messages.

DTMS:  Database and Transaction Management Services. Venerable CICS-like 8100/DPPX product for supporting interactive systems. For its time, it was a quite sophisticated and complex system, with such facilities as forward recovery, transaction back-out, multiple indexes, etc. Obsolete.

DTP1:  DeskTop Publishing. Generic term for systems which produce typeset quality artwork from a user workstation (e.g., a PC). The market has traditionally been dominated by Apple with its Macintosh.

DTP2:  Distributed Transaction Processing.

DTR1:  Distribution Tape Reel. Magnetic tape on which IBM distributes software.

DTR2:  See Dynamic Transaction Routing.

DTR3:  See Dedicated Token Ring.

DUA:  Distribution and Usage Authorization (sometimes Agreement). IBM contract, which allows users to distribute software to host-connected machines. It’s a sort of site license. Replaces the ATC program.

Dual Boot:  Originally, an OS/2 utility enabling users to load OS/2 and DOS from the same disk drive. Now a generic term used by Microsoft and others. For example, Windows 2000 has both dual boot and multi-boot capabilities, with other operating systems or just multiple copies of the same operating system.

Dual Copy:  Mirroring facility provided by the 3990 Storage Controller which maintains two identical copies of important data to give improved recovery. However, note that both the copies must be on disks downstream of the same controller which somewhat compromises the resilience since the controller is a single point of potential failure. Much delayed, and was finally delivered May 1990. Now an obsolete capability and not offered on the 2105, which replaced the 3990.

Dual porting:  PCM name for Device Level Select (DLS).

Dumb head:  IBMspeak for a dumb terminal.

Dump:  To copy data, at a particular instant, from one storage device to another. Dumping is usually for the purpose of collecting error information for analysis.

Dump Viewing Facility:  Originally replaced IPCS as the standard tool for reading all VM dumps. z/VM introduced the VM Dump Tool, but it has replaced the Dump Viewing Facility only for CP dumps. The Dump Viewing Facility continues to be the supported vehicle for reading non-CP (e.g., CMS) dumps.

DUOW:  See Distributed Unit Of Work.

Duplex:  A generic term for a mode of communication. In full duplex, both participants can transmit at the same time (typically over four wires), and in half duplex, only one participant can transmit at a time – each participant has to wait for the other to stop before transmitting.

Duplex pair:  A DASD logical volume consisting of two physical devices with all data recorded twice, once on each volume (as in 3990 Dual copy).

DVD:  Digital Video Disk. See DVD-R, DVD-RAM, DVD-ROM, DVD-V.

DVD-R:  Digital Video Disk – Recordable. A recordable CD format which allows the storage of 3.95GB on a single high density disk.

DVD-RAM:  Digital Video Disk – Random Access Memory. A recordable CD format which allows the storage of 2.6GB on a single high density disk.

DVD-ROM:  Digital Video Disk – Read Only Memory. Another CD format which allows the storage of several GB (it keeps growing) on a single high density disk.

DVD-V:  Digital Video Disk – Video.

DVF:  See Dump Viewing Facility.

DVI1:  Digital Video Interactive.

DVI2:  Digital Video Interface. An Intel interface (with accompanying products). DVI supports digital storage and retrieval of audio, computer graphics, and full motion video. Available for PCs for use in creating interactive video systems. See ActionMedia.

DVT:  Destination Vector Table.

DW:  See Displaywriter or DisplayWrite.

DWA:  See Direct Window Access.

DWS:  Dependent WorkStation. A synonym for MFI workstation.

DXT:  Data eXTract. Utility for extracting data (one-off or regularly) from a database. Its main use was to help move IMS and DL/I databases to DB2. Replaced by DataRefresher in October 1993. Withdrawn September 1995.

Dyadic:  A two-way tightly-coupled multiprocessor.

DYNALLOC:  Dynamic allocation. The z/OS term for allocating datasets from within a program without using JCL statements. Very useful, and widely used by TSO.

Dynamic I/O reconfiguration:  IBMspeak for the ability to connect and disconnect devices in an ESCON configuration without having to close everything down. Also known as hot-plugging.

Dynamic Link Library:  Generic term for a program or a routine that can be loaded by an application or as part of a program.

Dynamic load balancing:  Generic term for a way of automatically distributing the workload around a multi-processor complex so that the resources available to individual systems vary continuously according to how much resource is needed and how much is available. See also JES.

Dynamic memory array:  Memory technology introduced on the Summit ES/9000s in September 1991. The dynamic memory array performs pro-active self-diagnosis and preventive maintenance, so that when a predetermined error threshold is reached, it replaces the failed chip with a standby.

Dynamic path reconnect:  Feature in IBM I/O systems in which a channel can initiate an I/O and then free itself while the device is actually finding the data. Dynamic I/Os may be initiated on one channel and completed on another. Available under z/OS and VSE/ESA.

Dynamic resource allocation:  An allocation methodology in which the resources assigned for execution of computer programs are determined by criteria applied at the moment of need.

Dynamic SQL:  Generic term for SQL implementations in which the SQL statements are compiled/interpreted at run-time. DSL has the advantage over Static SQL of flexibility, bought usually at the cost of increased resource usage – authorizations, etc must be verified at run-time. The result is worse performance and security, and for distributed applications, there’s more network traffic. Also known as DSL.

Dynamic transaction routing:  Facility which allows the user to choose how to distribute transaction work across multiple CICS regions at execution time. Available internally within a CICSplex.