DDK Glossary - A

ABIOS

Advanced BIOS. See BIOS.

accelerator

In SAA Common User Access architecture, a key or combination of keys that invokes an application-defined function.

accelerator table

A table used to define which key strokes are treated as accelerators and the commands they are translated into.

access mode

The manner in which an application gains access to a file it has opened. Examples of access modes are read-only, write-only, and read/write.

access permission

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

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.

action

One of a set of defined tasks that a computer performs. Users request the application to perform an action in several ways, such as typing a command, pressing a function key, or selecting the action name from an action bar or menu.

action bar

In SAA Common User Access architecture, the area at the top of a window that contains choices that give a user access to actions available in that window.

action point

The current position on the screen at which the pointer is pointing. Contrast with hot spot and input focus.

active program

A program currently running on the computer. An active program can be interactive (running and receiving input from the user) or noninteractive (running but not receiving input from the user). See also interactive program and noninteractive program.

active window

The window with which the user is currently interacting.

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

(1) The range of addresses available to a program. (A)

(2) 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. (Also abbreviated as APA).

alphanumeric video output

Output to the logical video buffer when the video adapter is in text mode and the logical video buffer is addressed by an application as a rectangular array of character cells.

American National Standard Code for Information Interchange

The standard code, using a coded character set consisting of 7-bit coded characters (8 bits including parity check), that is used for information interchange among data processing systems, data communication systems, and associated equipment. The ASCII set consists of control characters and graphic characters. (A) Note: IBM has defined an extension to ASCII code (characters 128-255).

anchor

A window procedure that handles Presentation Manager message conversions between an icon procedure and an application.

anchor block

An area of Presentation Manager internal resources allocated to a process or thread that calls WinInitialize.

anchor point

The position or choice from which selection or deselection is extended. Also, a point in a window used by a program designer or by a window manager to position a subsequently appearing window.

ANSI

American National Standards Institute.

application

A collection of software components used to perform specific types of work on a computer; for example, a payroll application, an airline reservation application, a network application.

application object

In SAA Advanced Common User Access architecture, a form that an application provides for a user; for example, a spreadsheet form. Contrast with user object.

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

(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.

(3) In computer graphics, the width-to-height ratio of an area, symbol, or shape.

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. See also synchronous.

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 also 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

A 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.