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abbreviated installation. In the AS/400 system and System/38, an installation process in which verification and error recovery is done without restoring the saved version of the operating system. Contrast with normal installation.

abbreviation. An ordered and shortened representation of data that retains the identity of the data element that is represented. See also data code. (A)

abend. Abnormal end of task.

abend code. A system code that identifies the system message number and type of error condition causing the abend.

ABIC. Adaptive Bilevel Image Compression.

ABM. Asynchronous balanced mode.

ABME. Asynchronous balanced mode extended.

abnormal end. Synonym for abnormal termination.

abnormal end of task (abend). Termination of a task before its completion because of an error condition that cannot be resolved by recovery facilities while the task is executing.

abnormal termination. (1) The cessation of processing prior to planned termination. (T) (2) A system failure or operator action that causes a job to end unsuccessfully. (3) In System/38, termination by a means other than the successful execution of the Power Down System command. See normal termination, system termination. See also abnormal end of task (abend).

abort. In data communication, a function invoked by a sending primary, secondary, or combined station that causes the recipient to discard and ignore all bit sequences transmitted by the sender since the preceding flag sequences or to discard and ignore all data transmitted by the sender since the previous checkpoint.

aborted connection. In computer security, disconnection that does not follow established procedures, possibly enabling other users to gain unauthorized access.

abort sequence. A specified bit pattern, occurring anywhere in the bit stream, that is used to terminate transmission of a transmission frame prematurely. (T)

About.... (1) In SAA Common User Access architecture, a help action that displays ownership and copyright information about the application. (2) In SAA Common User Access architecture, a help action that displays the logo window of the application.

ABP. Actual block processor.

AB roll. In multimedia applications, synchronized playback of two recorded video images to perform effects such as dissolves, wipes, or inserts, using both images simultaneously.

absolute address. (1) A direct address that identifies a location without reference to a base address. An absolute address may itself be a base address. (T) (2) An address that is permanently assigned by the machine designer to a storage location. (A) (3) Synonymous with explicit address, machine address, specific address. (4) See base address, relative address.

absolute addressing. A method of addressing in which the address part of an instruction contains an absolute address. (I) (A)

absolute coding. Coding that uses computer instructions with absolute addresses. (A) Synonymous with specific coding.

absolute command. In computer graphics, a display command that causes the display device to interpret the data following the command as absolute coordinates. (I) (A) Synonymous with absolute instruction.

absolute coordinate. (1) One of a pair of coordinates that identify the position of an addressable point with respect to the origin of a specified coordinate system. (I) (A) Contrast with relative coordinate.

absolute data. In computer graphics, the values in a computer program that specify the actual coordinates in a display space or in storage. Contrast with relative data.

absolute device. A locating device, such as a tablet, that reports its position to the operating system as a set of numbers on a coordinate system.

absolute error. (1) The algebraic result of subtracting a true, specified, or theoretically correct value from the value computed, observed, measured, or achieved. (I) (A) (2) The amount of error expressed in the same units as the quantity containing the error. (A) (3) Loosely, the absolute value of the error, that is, the magnitude of the error without regard for its algebraic sign. (A)

absolute expression. An assembly-time expression whose value is not affected by program relocation. An absolute expression can represent an absolute address.

absolute instruction. (1) A computer instruction in its final, executable form. (I) (A) (2) Synonym for absolute command.

absolute loader. A routine that reads a computer program into main storage, beginning at the assembled origin. (A)

absolute order. Deprecated term for absolute command.

absolute positioning. Positioning an item of data with respect to an origin.

absolute priority. In the OS/2 operating system, pertaining to a priority of a process that is not varied by the operating system. Contrast with dynamic priority.

absolute term. A term whose value is not affected by relocation.

absolute value. The magnitude of a real number regardless of its algebraic sign.

absolute vector. (1) In computer graphics, a vector whose start and end points are specified in absolute coordinates. (I) (A) (2) Contrast with incremental vector. See also relative vector.

abstract symbol. (1) A symbol whose meaning and use have not been determined by a general agreement but have to be defined for each application of the symbol. (I) (A) (2) In optical character recognition, a symbol whose form does not suggest its meaning and use; these must be defined for each specified set of applications. (A)

AC. Alternating current.

Academy Studies. The body of work collectively performed by the IBM Academy, which is comprised of IBM Fellows and Senior Technical Staff members. Academy studies, which include analyses of key technical issues, are selected by the Academy members for research, then brought forward to senior management.

ACB. (1) Access method control block. (2) Adapter control block. (3) Application control block.

ACB address space. In VTAM, the address space in which the ACB is opened. See also associated address space, session address space.

ACB-based macroinstruction. In VTAM, a macroinstruction whose parameters are specified by the user in an access method control block.

ACBGEN. Application control block generation.

ACB name. (1) The name of an ACB macroinstruction. (2) A name specified either on the VTAM APPL definition statement or on the VTAM application program's ACB macroinstruction. Contrast with network name.

ACC. (1) Accumulate. (2) Accumulator. (3) Application control code.

acceleration time. That part of access time required to bring an auxiliary storage device, typically a tape drive, to the speed at which data can be read or written.

accelerator. (1) In the AIXwindows program, a keyboard alternative to a mouse button action; for example, holding the <Shift> and <M> keys on the keyboard can be made to post a menu in the same way that a mouse button action does. Accelerators typically provide increased input speed and greater convenience. (2) In SAA Common User Access architecture, a key or combination of keys that invokes an application-defined function.

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accept. (1) In a VTAM application program, to establish a session with a logical unit (LU) in response to a CINIT request from a system services control point (SSCP). The session-initiation request may begin when a terminal user logs on, a VTAM application program issues a macroinstruction, or a VTAM operator issues a command. See also acquire. (2) An SMP process that moves distributed code and MVS-type programs to the distribution libraries.

acceptance test. A test of a system or functional unit, usually performed by users on their premises after installation, with the participation of the vendor to ensure that contractual requirements are met. (I) (A)

accept-command-key indicator (AC indicator). In the System/36 workstation utility, an indicator that signals the status of any current user-defined command key request.

accepting station. In systems with ACF/TCAM, a destination station that accepts a message.

accept-sequence-error indicator (AE indicator). An indicator that allows operators to bypass required displays.

access. (1) To obtain the use of a computer resource. (T) (2) The use of an access method. See (A) (3) The manner in which files or data sets are referred to by the computer. (4) To obtain data from or to put data in storage. (5) In computer security, a specific type of interaction between a subject and an object that results in the flow of information from one to the other. See read access, write access. (6) In FORTRAN, the means by which a scoping unit accesses entities in a module subprogram or, in the case of an internal procedure, in its host. Such entities may be explicitly or implicitly accessible. Access is provided by the USE statement. (7) See direct access, direct access storage, dynamic access, immediate access storage, indexed access, indexed sequential access, random access, remote access, sequential access, serial access.

access arm. (1) In a magnetic disk unit, an arm on which magnetic heads are mounted. (T) (2) A part of a magnetic disk storage unit that is used to hold one or more reading and writing heads. (A)

access authority. An authority that relates to a request for a type of access to data.

access barred. In data communication, a condition in which a data terminal equipment (DTE) cannot call the DTE identified by the selection signals.

access capability. (1) In computer security, a "ticket" that allows its holder to gain a specified type of access to a specified object; for example, to erase a specified file. (2) See capability.

access category. In computer security, a class to which a user may be assigned, based on the resources that the user is authorized to use.

Note: The access category determines a user's access rights.

access channel control. In the IBM Token-Ring Network, the logic and protocols that manage the transfer of data between link stations and medium access control (MAC).

access code. (1) In the AS/400 system, a 4-digit number, assigned to documents and folders, that allows authorized users to access the documents and folders. (2) In DPCX, an 8-bit binary code, assigned to a program that determines the terminal operators who are to be allowed to use the program.

access control. (1) In computer security, ensuring that the resources of a computer system can be accessed only by authorized users in authorized ways. See discretionary access control, identity-based access control, information flow control, mandatory access control, resource-based access control. (2) A technique used to establish the sequence of data stations that are in temporary control of the transmission medium, but may need to be moved elsewhere. (T)

access control byte. In the IBM Token-Ring Network, the byte following the start delimiter of a token or frame that is used to control access to the ring.

access control field. (1) A bit pattern that identifies whether a frame is a token, indicates the data stations that may use the token, indicates when the frame should be canceled, and allows stations to request the next token. (T) (2) In 8100, the field of a translation table entry that controls the types of storage access permitted during fetching and execution of an instruction or during a channel I/O operation.

access control key. Synonym for privacy key. (A)

access controller. In an information resource directory system with entity-level security, a pair of locks, one for read access, the other for write access. Locks may be used for other purposes, such as to permit execution. (A)

access control list. (1) In computer security, a collection of all access rights for one object. (2) In computer security, a list associated with an object that identifies all the subjects that can access the object and their access rights; for example, a list associated with a file that identifies users who can access the file and identifies their access rights to that file. See capability list. (3) In the AIX operating system, a file attribute that contains the basic and extended permissions that control access to the file. (4) In the AIX operating system, a list of hosts, maintained by Enhanced X-Windows, that have access to client programs. By default, only programs on the local host and those in this list can use the display. The list can be changed by clients on the local host; some server implementations can also modify the list. The authorization protocol name and data received by the server at connection setup may also affect this list. Synonymous with access list.

access control lock. Synonym for privacy lock. (A)

Access Control -- Logging and Reporting. In VSE, an IBM licensed program used to log access to protected data and to print selected formatted reports on such access.

access environment. A description of the current user, including user ID, current connect group, user attributes, and group authorities. An access environment is constructed during user identification and verification.

access key. In an information resource directory system with entity-level security, an authorization to perform a set of operations on an entity secured by a lock. (A)

access level. (1) In computer security, the level of authority a subject has when using a protected resource; for example, authority to access a particular security level of information. (2) In computer security, the hierarchical portion of the security level used to identify the sensitivity of data and the clearance or authorization of users. (3) In the IBM LinkWay product, the characteristic of a folder that determines how much a user can modify the folder. The access level is determined by the person who creates the folder.

access line. A telecommunication line that continuously connects a remote station to a data switching exchange (DSE). A telephone number is associated with the access line.

access list. Synonym for access control list. See also standard access list.

access lock. Synonym for privacy lock. (A)

access macro. A macroinstruction that establishes the linkage between a program requesting execution of a system routine and the system routine requested.

access matrix. In computer security, a two-dimensional array, one dimension of which represents objects and the other dimension subjects, where the intersections represent permitted access types.

access mechanism. (1) A mechanism responsible for moving an access arm or a comb. Synonymous with actuator. (T) (2) A group of access arms that move together as a unit.

Figure 2. Access Mechanism

access method. (1) A technique to obtain the use of data, storage, or the use of an input/output channel to transfer data; for example, random access method, sequential access method. (T) (2) The technique that is used to locate data stored on a physical medium. (A) (3) A technique for moving data between main storage and input/output devices. (4) The way that a system refers to records in files; the reference can be consecutive (records are referred to one after another in the order in which they appear in the file) or it can be random (the individual records are referred to in any order).

access method control block (ACB). A control block that links an application program to VSAM or VTAM programs.

access method interface (AMI). The TCAM function for managing communication on the access method control block (ACB) interface between TCAM and VTAM programs.

access method routines. Routines that move data between main storage and input/output devices.

access method services (AMS). The facility used to define and reproduce VSAM key-sequenced data sets (KSDS).

access mode. (1) A technique that is used to obtain a particular logical record from, or to place a particular logical record into, a file assigned to a mass storage device. (A) (2) The manner in which files are referred to by a computer. Access can be sequential (records are referred to one after another in the order in which they appear on the file), access can be random (the individual records can be referred to in a nonsequential manner), or access can be dynamic (records can be accessed sequentially or randomly, depending on the form of the input/output request). (3) In COBOL, the manner in which records are to be operated upon within a file. (4) See file access mode. See also random access, sequential access.

access name. (1) In a database, a name that identifies an entity. (2) In an information resource dictionary, the name by which an entity is known to the user interfaces. It is the combination of an assigned access name and version identifier that together serve as the primary identifier of each entity. (A)

accessor. (1) In computer security, any user of a protected resource. (2) In MSS, the component of the IBM 3851 Mass Storage Facility that transports data cartridges between the cartridge cells, data recording devices, and the cartridge access station.

accessor control. In MSS, the component of the IBM 3851 Mass Storage Facility that decodes and sequences messages from the mass storage control and directs the motion of the accessor.

accessor environment element (ACEE). In RACF, a description of the current user including userid, current connect group, user attributes, and group authorities. An ACEE is constructed during user identification and verification.

accessory. (1) A basic part, subassembly, or assembly used with another assembly, unit, or set. (2) A separately orderable part that has no type number, is for purchase only, and does not receive normal IBM maintenance.

access path. (1) A sequence of data items used by a database management system to access records or other data items stored in a database. There may simultaneously exist more than one access path for one data item. (T) (2) A chain of addresses that leads to the desired data. (A) (3) The procedure used by a database management system to access data stored in a database. (A) (4) The order in which records in a database file are organized for processing by a program. See arrival sequence access path, keyed sequence access path. (5) In SQL, the path used to locate data specified in SQL statements. An access path can be indexed, sequential, or a combination of both.

access path independence. The independence of logical data descriptions on access paths. Programs using access path independent logical data descriptions need not be changed when access paths are changed. (T)

access path journaling. A method of recording changes to an access path as changes are made to the data in the database file so that the access path can be recovered automatically by the system.

access period. In computer security, a period of time during which specified access rights prevail.

access permission. (1) All of a user's access rights. (A) (2) All access rights a user has regarding an object. (I) (3) In the AIX operating system, a group of designations that determine who can access a particular file and how the user can access the file. See base permission, extended permission. See also permission code.

access plan. In SQL, the control structure produced during compile time that is used to process SQL statements encountered when the program is run.

access priority. In the IBM Token-Ring Network, the maximum priority that a token can have for transmission via the token-ring adapter.

access procedure. The procedure or protocol used to gain access to a shared resource; for example, in a local area network the shared resource is the transmission medium. The medium access procedures specified by the IEEE 802 standard are CSMA/CD token, bus, and ring.