DDK Glossary - D

Glossary

DAC

Digital-to-analog converter.

DASD

Direct-access storage device. A device in which access time is effectively independent of the location of the data.

data bus

A bus used to communicate data internally and externally to and from a processing unit, storage, and peripheral devices. (A) See bus.

data object

In an application, an element of a data structure (such as a file, an array, or an operand) that is needed for program execution and that is named or otherwise specified by the allowable character set of the language in which the program is coded.

data segment

A nonexecutable section of a program module; that is, a section of a program that contains data definitions.

data stream

All data transmitted through a data channel.

data streaming

Real-time, continuous flowing of data.

data structure

The syntactic structure of symbolic expressions and their storage-allocation characteristics. (T)

data transfer

The movement of data from one object to another by way of the clipboard or by direct manipulation.

DBCS

Double-byte character set. A set of characters in which each character is represented by two bytes. Languages such as Japanese, Chinese, and Korean, which contain more characters than can be represented by 256 code points, require double-byte character sets. Because each character requires 2 bytes, the typing, display, and printing of DBCS characters requires hardware and programs that support DBCS. Contrast with single-byte character set.

DCP

See device control panel.

DDB

Device-dependent bit map.

DDE

Dynamic data exchange. A message protocol used to communicate between applications that share data. The protocol uses shared memory as the means of exchanging data between applications.

deadlock

(1) Unresolved contention for the use of a resource. (2) An error condition in which processing cannot continue because each of two elements of the process is waiting for an action by, or a response from, the other. (3) An impasse that occurs when multiple processes are waiting for the availability of a resource that will not become available because it is being held by another process that is in a similar wait state.

debug

To detect, diagnose, and eliminate errors in programs. (T)

decode

(1) To convert data by reversing the effect of previous encoding. (2) To interpret a code. (3) To convert encoded text into plaintext by means of a code system. (4) Contrast with encode.

decipoint

In printing, one tenth of a point. There are 72 points in an inch.

default procedure

A function provided by the Presentation Manager Interface that may be used to process standard messages from dialogs or windows.

default value

A value assumed when no value has been specified. Synonymous with assumed value. For example, in the graphics programming interface, the default line-type is 'solid'.

default video window

(1) Refers to where video is displayed when an application does not indicate an application-defined window with the MCI_WINDOW message. This is provided by and managed for the application by MMPM/2. (2) See also application-defined window.

default window

See default video window.

definition list

A type of list that pairs a term and its description.

deinstantiation

See instantiation.

delta

An application-defined threshold, or number of container items, from either end of the list.

delta frame

Refers to one or more frames occurring between reference frames in the output stream. Unlike a reference frame, which stores a complete image, a delta frame stores only the changes in the image from one frame to the next. See reference frame.

Deselect all

A choice that cancels the selection of all of the objects that have been selected in that window.

destination rectangle

An abstract region which defines the size of an image to be created when recording images for software motion video playback. The ratio of this rectangle's size to that of the source rectangle determines the scaling factor to be applied to the video.

destination window

See destination rectangle.

Desktop Manager

In the Presentation Manager, a window that displays a list of groups of programs, each of which can be started or stopped.

desktop window

The window, corresponding to the physical device, against which all other types of windows are established.

detached process

A background process that runs independent of the parent process.

detent

A point on a slider that represents an exact value to which a user can move the slider arm.

device capabilities

The functionality of a device, including supported component functions.

device context

(1) A logical description of a data destination such as memory, metafile, display, printer, or plotter. (2) The device status and characteristics associated with an opened instance of an Media Control Interface device. See also direct device context, information device context, memory device context, metafile device context, queued device context, and screen device context.

device control panel (DCP)

An integrated set of controls that is used to control a device or media object (such as by playing, rewinding, increasing volume, and so on).

device controls

See standard multimedia device controls.

device driver

(1) A file that contains the code needed to attach and use a device such as a display, printer, or plotter. (2) A program that enables a computer to communicate with a specific peripheral device; for example, a printer, a videodisc player, or a CD drive.

device driver initialization (init) time

See initialization (init) time, device driver.

device driver profile

A file with a "DDP" extension, containing a script that is interpreted by the OS/2 DDINSTAL utility. Among other things, it defines which files to copy from installation diskettes to target directories and specifies how the CONFIG.SYS file will be updated.

device element

A data object, such as a file, utilized by a compound device.

device helper (DevHlp)

(1) A kernel service (memory, hardware interrupt, software interrupt, queuing, semaphore, and so forth) provided to physical device drivers. (2) A callable C-language or assembler-language routine that provides an operating system service for an OS/2 device driver.

device object

A device that provides a means of communication between a computer and the outside world. A printer is an example of a device object.

device sharing

(1) The ability to share a device among many different applications simultaneously. If a device is opened shareable, the device context will be saved by the operating system when going from one application to another application. (2) Allowing a device context to be switched between Media Control Interface devices.

device space

(1) Coordinate space in which graphics are assembled after all GPI transformations have been applied. Device space is defined in device-specific units. (2) (D of C) In computer graphics, a space defined by the complete set of addressable points of a display device. (A)

device table

A data structure containing a summary of the adapters an adapter device driver supports and a list of the I/O devices attached to each adapter. This data structure is built by the adapter device driver in response to an IOCC_CONFIGURATION IOCM_GET_DEVICE_TABLE request.

device-specific format

The storage or transmission format used by a device, especially if it is different from an accepted standard.

dialog

(1) The interchange of information between a computer and its user through a sequence of requests by the user and the presentation of responses by the computer. (2) In an interactive system, a series of related inquiries and responses similar to a conversation between two people.

dialog box

In SAA Advanced Common User Access architecture, a movable window, fixed in size, containing controls that a user uses to provide information required by an application so that it can continue to process a user request. See also message box, primary window, secondary window. Also known as a pop-up window.

Dialog Box Editor

A WYSIWYG editor that creates dialog boxes for communicating with the application user.

dialog item

A component (for example, a menu or a button) of a dialog box. Dialog items are also used when creating dialog templates.

dialog procedure

A dialog window that is controlled by a window procedure. It is responsible for responding to all messages sent to the dialog window.

dialog tag language

A markup language used by the DTL compiler to create dialog objects. Synonymous with DTL.

dialog template

The definition of a dialog box, which contains details of its position, appearance, and window ID, and the window ID of each of its child windows.

digital

(1) Pertaining to data in the form of numeric characters. (2) Contrast with analog.

digital audio

(1) Material that can be heard that has been converted to digital form. (2) Synonym for digitized audio.

digital signal processor (DSP)

A high-speed coprocessor designed to do real-time manipulation of signals.

digital video

(1) Material that can be seen that has been converted to digital form. (2) Synonym for digitized video.

digital video effects (DVE)

An online editing technique that manipulates on-screen a full video image; activity for creating sophisticated transitions and special effects. Digital video effects (DVE) can involve moving, enlarging, or overlaying pictures.

Digital Video Interactive (DVI)

A system for bringing full-screen, full-motion television pictures and sound to a regular PC. DVI is a chip set and uses delta compression; that is, only the image-to-image changes in each frame are saved rather than the whole frame. Data (video footage) is compressed into a form that reduces memory requirements by factors of 100 or greater. This compressed data is stored on optical discs and can be retrieved at a rate of 30 frames per second. (The DVI technology was developed by RCA and then sold to Intel. IBM has chosen this technology for future use in the PS/2.)

digital-to-analog converter (DAC)

(1) A functional unit that converts data from a digital representation to an analog representation. (2) A device that converts a digital value to a proportional analog signal.

digitize

To convert an analog signal into a digital format. (An analog signal during conversion must be sampled at discrete points and quantized to discrete numbers.)

digitized audio

Synonym for digital audio.

digitized video

Synonym for digital video.

digitizer

A device that converts data to digital format any image into a computer.

direct device context

A logical description of a data destination that is a device other than the screen (for example, a printer or plotter), and where the output is not to go through the spooler. Its purpose is to satisfy queries. See also device context.

direct manipulation

(1) The user's ability to interact with an object by using the mouse, typically by dragging an object around on the Desktop and dropping it on other objects. (2) A set of techniques that allow a user to work with an object by dragging it with a pointing device or interacting with its pop-up menu.

direct memory access

(1) A technique for moving data directly between main storage and peripheral equipment without requiring processing of the data by the processing unit. (2) The transfer of data between memory and input/output units without processor intervention.

direct-read-after-write (DRAW) disc

A videodisc produced directly from a videotape, one copy at a time. A DRAW disc usually is used to check program material and author applications before replicated discs are available.

directory

A type of file containing the names and controlling information for other files or other directories.

disc

Alternate spelling for disk.

discard stop

In data streaming, requests that the data stream be stopped and the data remaining in the stream buffers be discarded.

disk

A round, flat, data medium that is rotated in order to read or write data.

display frame

(1) In computer graphics, an area in storage in which a display image can be recorded. (2) In computer micrographics, an area on a microform in which a display image can be recorded.

display image

See definition list.

display point

Synonym for pel.

dissolve

To fade down one picture as the next fades up. Synonym for crossfade.

dithering

(1) The process used in color displays whereby every other pel is set to one color, and the intermediate pels are set to another. Together they produce the effect of a third color at normal viewing distances. This process can only be used on solid areas of color; it does not work, for example, on narrow lines. (2) In computer graphics, a technique of interleaving dark and light pixels so that the resulting image looks smoothly shaded when viewed from a distance. (3) When different pixels in an image are prebiased with a varying threshold to produce a more continuous gray scale despite a limited palette. This technique is used to soften a color line or shape. This technique also is used for alternating pixel colors to create the illusion of a third color.

DLL

Dynamic-link library.

dolly

A wheeled platform for a camera; a camera movement where the tripod on which the camera is mounted physically moves toward or away from the subject.

DOS IOProc

An internal I/O procedure, provided by the MMPM/2 system, that supports DOS files.

DOS Protect Mode Interface (DPMI)

An interface between protect mode and real mode programs.

double-click

In SAA Advanced Common User Access, to press and release a mouse button twice within a time frame defined by the user, without moving the pointer off the choice. See click. See also drag select.

doubleword

A contiguous sequence of bits or characters that comprises two computer words and is capable of being addressed as a unit. (A)

drag

In SAA Common User Access, to use a pointing device to move an object; for example, clicking on a window border, and dragging it to make the window larger.

drag select

In SAA Advanced Common User Access, to press a mouse button and hold it down while moving the pointer so that the pointer travels to a different location on the screen. Dragging ends when the mouse button is released. All items between the button-down and button-up points are selected. See also click, double-click.

dragging

(1) In computer graphics, moving an object on the display screen as if it were attached to the pointer. (2) In computer graphics, moving one or more segments on a display surface by translating. (I) (A)

DRAW disc

Direct-read-after-write disc.

driver

(1) A program (and possibly data files) that contain information needed to run a particular unit, such as a plotter, printer, port, or mouse. See also device driver and printer driver. (2) A system or device that enables a functional unit to operate.

drop

To fix the position of an object that is being dragged, by releasing the select button of the pointing device. See also drag.

drop-frame time code

A nonsequential time code used to keep tape time code matched to real time. Must not be used in tapes intended for videodisc mastering.

DSP

Digital signal processor.

DTL

Dialog tag language. See dialog tag language.

dual-boot function

A feature of the OS/2 operating system that allows the user to start DOS from within the operating system, or an OS/2 session from within DOS.

dual plane video system

Refers to when graphics from the graphics adapter are separate from the analog video. That is, there is a separate graphics plane and video plane. The analog video appears behind the graphics, showing through only in the areas that are transparent. Since graphics and video are separate, capturing the graphics screen will only obtain graphics, and capturing the video screen will only obtain video. This is also true for restoring images. See also single plane video system.

dual-state push button

A push button that has two states, in and out. It is used for setting and resetting complementary states, such as Mute and Unmute.

dual-tone modulation frequency (DTMF)

Pushbutton phone tones.

dub

To copy a tape; to add (sound effects or new dialog) to a film; to provide a new audio track of dialog in a different language. (Often used with "in" as "dub in".)

duplex

Pertaining to communication in which data can be sent and received at the same time. Synonymous with full duplex.

DVE

Digital video effects.

DVI

Digital Video Interface.

dynamic data formatting

A formatting procedure that enables you to incorporate text, bit maps, or metafiles in an IPF window at execution time.

dynamic icon

An icon that changes to convey some information about the object that it represents. For example, a folder icon can show a count, indicating the number of objects contained within the folder. Also, a tape player icon can show an animation of turning wheels to indicate that the machine playing.

dynamic link library (DLL)

(1) A file containing executable code and data bound to a program at load time or run time, rather than during linking. The code and data in a dynamic link library can be shared by several applications simultaneously. (2) A file containing executable code and data bound to a program at load time or run time, rather than during linking. The code and data in a dynamic link library can be shared by several applications simultaneously.

dynamic linking

(1) The process of resolving external references in a program module at load time or run time rather than during linking. (2) In the OS/2 operating system, the delayed connection of a program to a routine until load time or run time.

dynamic resource

A multimedia program unit of data that resides in system memory. Contrast with static resource.

dynamic resource allocation

An allocation technique in which the resources assigned for execution of computer programs are determined by criteria applied at the moment of need. (I) (A)

dynamic segments

Graphics segments drawn in exclusive-OR mix mode so that they can be moved from one screen position to another without affecting the rest of the displayed picture.

dynamic storage

(1) A device that stores data in a manner that permits the data to move or vary with time such that the specified data is not always available for recovery. (A) (2) A storage in which the cells require repetitive application of control signals in order to retain stored data. Such repetitive application of the control signals is called a refresh operation. A dynamic storage may use static addressing or sensing circuits. (A) (3) See also static storage.

dynamic time slicing

Varies the size of the time slice depending on system load and paging activity.

dynamic-link module

A module that is linked at load time or run time.