DAC
Digital-to-Analog Converter. Device takes a computer's
digital input signals, made up of 1s and 0s, and converts
them to analog output signals for use with such external
devices as VGA (Video Graphics Adapter) monitors, analog
VCRs, speakers, etc.
.DAT
A virus-signature-update file format used by McAfee Network Security and Management for automatic SecureCast installation on the desktop.
Data and Resource Forks
Both are used by the MacOS to construct graphics; Windows uses only the Data Fork.
.DBF
A database file. The extension has been used by dBASE's PC database for its files and by various other database and spreadsheet applications for their files which may be interchanged with the dBASE application. Files with this extension can be accessed by a MacOS system with most Mac databases. The file has this creator type: TEXT and this File Type: DBF.
.DCA
Document Content Architecture file (v2.0).
.DCS
Desktop Color Separation file format.
Decibel (dB)
For a sound, the numerical expression of its loudness as measured on a scale with the smallest increment corresponding to the smallest difference in sound that the human ear can hear.
Degas
Atari ST data file format that supports 2-, 4-, or 16-color graphics. Files may have a filename extension of: .PLN.
.DHR, DHRP
An Apple IIe and IIc graphic file format. Both packed (compressed) and unpacked, may have one of two graphic data-formats (560 (h) by 192 (v) pixel): Double Hi-Res Black and White (B&W) 2 color data-format. (An unpacked file's filename extension is: DHR; a packed file's filename extension is: DHRP.) The double Hi-Res data-format with 16 colors has a filename extension of: DHRP.
.DIF
Data Interchange Format. PC files with this extension can be accessed by a MacOS system with Microsoft's Excel. The file has this creator type: XCEL and this File Type: TEXT.
Digital
VCR Multimedia data-format for MacOS and DOS/Windows. Its video picture is "better than provided by current analog devices" Specifications: 11 Gbytes of data storage or 4.5 hours or video per standard VCR tape, (1 hour on a minicasstte); transfer rate is 25 Mbps.
Digital uses proprietary discrete cosine transform compression/de-compression (codec). Supports NTSC, U.S. HDTV and Japanese HDTV formats. Permits merging of consumer video and multimedia authoring; but, "without the random access of a CD."
Digitize
To convert images from an analog to a digital-data format (of 1s and 0s) for data-storage and processing. Digitizing video includes two options. The first is "Step-time capture," which gives a computer control of the advance rate of each frame of video so that one frame at a time can be digitized. Digitizing video played at normal speed is termed: "Real-time capture."
.DIR, .DCR
Macromedia's Director movie file format. Use Macromedia's Afterburner utility compresses the file, its filename extension will change to DCR.
Dithering
Dithering fools the human eye into seeing more colors than are actually present in an image by blending many adjacent colors into a single apparent color. For example, this technique is used to convert "real world" colorful 24-bit images to 8-bit for playback on DOS and Mac computers.
Graphic-image manipulation software "indexes" the image's colors to the computer's standard color lookup table (CLUT), color palette or a customized best-match "adaptive color palette" by software. A visual problem may arise if two or more images are displayed on screen, each having a different color palette.
DL
DOS motion video file format. Player utility: DL-VIEW (DOS shareware).
.DLL
Dynamic Link Library is an executable file format containing procedures and subroutines, including the ability to load and unload as required, which can be called by all Windows-compatible software. For example, a ISACOMM.DLL file may be created in Borland's C++ to let Microsoft Visual Basic read and write to the ISA bus.
.DOC
MS-Word document. PC files with this extension can be accessed by a MacOS system with Microsoft's Word. The file has this creator type: MSWD and this File Type: TEXT.
.DOT
Microsoft Word template. (Such files can be infected by a macro virus.)
DPI
Dots Per Inch measures an image's density of resolution as related to the number of dots a printer (or other output device) can print per inch (horizontal by vertical). The MacOS standard is 72 dpi on screen, but any dpi may be used.
.DOC
A document file. Microsoft Word uses the extension for its text files.
Downsampling
For a sound being converted from an analog to a digital form--to reduce its file size--its sampling rate is reduced (and so to its fidelity).
DPaint™
ANIM DOS/Windows DeluxPaint™ animation data-format. Supports multiple images, each with the same width and height, in a single file. Image frames are typically 320 by 200 pixels (8-bits per pixel). Frames are accessed in sequence. When opening a file, if you request a frame other than the first frame, all preceding frames must be opened first because frames are stored as the difference from the previous frame. Files may have a filename extension of: .ANM. Note, format is incompatible with the Amiga DPaint III "Anim" IFF data-format.
.DTB
An SpDE (back annotation) delay file which can be used by ViewLogic VSM's NetLister.
DTD
Document Type Definitions creates the basic structure for both SGML (Standard Generalized Markup Language) and HTML (Hypertext Markup Language) applications. The DTD for a a SGML application could define over 200 tags, while the DTD for HTML might be limited to 8 basic tags.
DVD
Divital Versatile (or Video) Disk and drive, and data-storage format. (See Sections 11 and 12.)
.DVI
Digital Video Interactive motion-video file format developed by Intel Corporation to provide a compression algorithm for full-screen, full-motion video.
DVI ( RTV, PVL)
Digital Video Interleaved, compression/decompression (codec) format. Used for storing video on digital media. It is based on a VQ (vector quantization) algorithm. There are two formats: a symmetric real-time video (RTV) codec and an asymmetric production-level video (PVL).
RTV, which runs on the Intel/IBM Action Media II board can display video in a window of 259 (h) by 240 (v) pixels at 15 frames per second (fps). Another term for symmetrical is bidirectional, which means that it takes the same amount of time to compress the video as to decompress it.
PVL can playback video at 604 (h) by 480 (v) pixels at 30 fps. With asymmetric schemes, compressions are slower than decompressions. PVL frame compressions are much slower than RTV, playback quality is much better and at a data rate suitable for single-speed CD-ROM.
.DXA
Data Exchange Agent file format. It can contain hooks into applications that use ActiveX controls to boost performance for remote uses.
.DXF
Drawing Interchange File is Autodesk 's graphics data-format for AutoCAD on DOS/Windows systems.
Dynamic rang
For a sound, the degree of its loudness or softness in playback as measured between its amplitude (without clipping distortion) to the smallest decibel (that can be heard).
References are samples only. Each one is presented in greater detail in the
Technical Research Assistant for 2001
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