DDK Glossary - A

ABIOS: Advanced BIOS. See BIOS.
accumulator

A register in which one operand of an operation can be stored and subsequently replaced by the result of that operation. (T)
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 conversion: The process of converting a 0:32 memory reference to the 16:16 addressing scheme, and vice versa.
address space

The range of addresses available to a program. (A)
The area of virtual storage available for a particular job.

address translation: (1) The process of resolving a 0:32 memory reference into a physical memory address. When using the paged memory option in the 80386 processor, a memory pointer passed by an application consists of Page Directory and Page Table entries, and an offset within a physical page. This is resolved by the processor into a 32-bit physical memory address. The validity and legality of the memory reference is also checked during the translation process, and a general protection exception is generated if necessary.; (2) The process of resolving a 16:16 memory reference into a physical memory address using a process's local descriptor table. The validity and legality of the memory reference is also checked during the translation process, and a general protection exception is generated if necessary.
alias: Term used in the 80386 segmented memory model, to refer to the case where two different addresses reference the same physical memory location; the location is said to be aliased. This technique is used when sharing memory between processes, and when mapping memory references between 16:16 and 0:32 addressing schemes.
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.
application-modal: Pertaining to a message box or dialog box for which processing must be completed before further interaction with any other window owned by the same application may take place.
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.
arena: Refers to a contiguous subset of the processor's virtual address space. In OS/2 V2.0, arenas are used to manage regions of the linear address space.
ASCII: American National Standard Code for Information Interchange.
ASCIIZ: A string of ASCII characters that is terminated with a byte containing the value 0.
aspect ratio

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.
On a display screen, the ratio of the maximum length of a display line to the maximum length of a display column.

asynchronous (ASYNC)

Pertaining to two or more processes that do not depend upon the occurrence of specific events such as common timing signals. (T)
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.
atomic operation: An operation that completes its work on an object before another operation can be performed on the same object.
attribute: nA characteristic or property that can be controlled, usually to obtain a required appearance; for example, the color of a line. See also graphics attributes and segment attributes.
automatic link: In Information Presentation Facility (IPF), a link that begins a chain reaction at the primary window. When the user selects the primary window, an automatic link is activated to display secondary windows.
AVIO: Advanced Video Input/Output