## Display Device Driver Reference for OS/2

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### Glossary - A

A

ABIOS - Advanced BIOS. See BIOS.

accumulator - (1) A register in which one operand of an operation can be stored and subsequently replaced by the result of that operation. (T) (2) In the IBM 3800 Printing Subsystem Models 3 and 8, a feature that supplies a separate storage that can hold data in raster form. It can be used either for composing a sheet of data that combines a large amount of variable and constant data, or for storing an electronic overlay in raster form that will be merged with variable data as the sheet is printed.

access permission - All access rights a user has regarding an object. (I)

adapter - A piece of hardware that modifies the system unit to allow it to operate in a particular way, often by connecting the system unit to an external device such as a video monitor.

adapter device driver - A device driver that provides hardware-dependent services for an OEM adapter.

address space - (1) The range of addresses available to a program. (A) ( 2) The area of virtual storage available for a particular job.

all points addressable (APA) - In computer graphics, pertaining to the ability to address and display or not display each picture element (pel) on a display surface.

anchor block - An area of the internal resources of OS/2 Presentation Manager which is allocated to a process or thread that calls WinInitialize.

anchor point - The position or choice from which selection or deselection is extended.

APA - All points addressable.

API - Application programming interface.

application programming interface (API) - A functional interface supplied by the operating system, or by a separately-orderable licensed program, that allows an application program written in a high-level language to use specific data or functions of the operating system or the licensed program.

archive flag - In the OS/2 operating system, a flag of files and directories that the operating system uses to determine which files are new or modified. Files with this flag are included when a backup copy is made or when all the files are restored on a hard disk. See flag.

area - In computer graphics, a filled shape such as a solid rectangle.

ASCIIZ - A string of ASCII characters that is terminated with a byte containing the value 0.

aspect ratio - (1) The ratio of the height of a rectangle to its width. A rectangle of width 10 inches and height 5 inches has an aspect ratio of 10/ 5 or 2. (2) On a display screen, the ratio of the maximum length of a display line to the maximum length of a display column.

asynchronous (ASYNC) - (1) Pertaining to two or more processes that do not depend upon the occurrence of specific events such as common timing signals . (T) (2) Without regular time relationship; unexpected or unpredictable with respect to the execution of program instructions.

atom - A constant that represents a string. Once a string has been defined as an atom, the atom can be used in place of the string to save space. Strings are associated with their respective atoms in an atom table. See integer atom.

atom table - A table used to associate atoms with the strings that they represent. This table contains the mechanism by which the presence of a string can be verified.

AVIO - Advanced Video Input/Output