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Glossary
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data compression. To take files on a disk and make them smaller. Often used for transmitting files through a modem (thereby reducing the time spent on the phone) and for storing files on a hard disk so that they take up less space. You have to uncompress them before you can use them.
data fork. On the Macintosh, all files have two parts: a resource fork and a data fork. The data fork usually contains information (that is, the actual data) that the program needs to run. The resource fork usually contains the instructions for running a program or other necessary resource information, such as fonts, icons, menus, and so on.
database. An organized collection of information (data).
DCE. (1) Short for Distributed Computing Environment, a suite of technology services developed by The Open Group for creating distributed applications that run on different platforms. DCE services include: Remote Procedure Calls (RPC) Security Service Directory Service Time Service Threads Service Distributed File Service DCE is a popular choice for very large systems that require robust security and fault tolerance. (2) Short for Data Communications Equipment, a device that communicates with a Data Terminal Equipment (DTE) device in RS-232C communications. See DTE for more information.
DCOM. Short for Distributed Component Object Model, an extension of the Component Object Model (COM) to support objects distributed across a network. DCOM was developed by Microsoft and has been submitted to the IETF as a draft standard. Since 1996, it has been part of Windows NT, and is also available for Windows 95. DCOM serves the same purpose as IBM's DSOM protocol, which is the most popular implementation of CORBA. Unlike CORBA, which runs on many operating systems, DCOM is currently implemented only for Windows.
decoder. A device used to recover the component signals from a composite (encoded) source. Decoders are used in displays and in various processing hardware where component signals are required from a composite source.
decryption. To convert indecipherable gibberish into plain English that everyone can understand.
de facto standard. A format, language, or protocol that has become a standard not because it has been approved by a standards organization but because it is widely used and recognized by the industry as being standard. Some examples of de facto standards include: Hayes command set for controlling modems; Kermit Communications Protocol; Xmodem Communications Protocol; Hewlett-Packard Printer Control Language (PCL) for laser printers; PostScript page description language for laser printers
delay line. A device designed to delay the video signal for a specific length of time. Required when switching between different types of devices or cameras with significatly different cable lengths.
demodulate. To recover the information being transmitted by a modulated signal. For example, a conventional TV receiver demodulates an incoming broadcase signal to convert it into the luminance and chrominance information displayed by the CRT and the sound emitted by the speaker.
demodulator. A devide which strip the video and audio signals from the carrier frequency.
desktop. The blank screen (background) that appears on programs that use a graphical user interface, also referred to as GUI (pronounced goo-ey), such as the Macintosh, Windows, or OS/2.
desktop publishing. To combine text and pictures on a computer screen to create neat-looking newsletters, books, or brochures.
desktop viewing. The ability to use the computer screen to view the output of a project of an interpersonal and corporate communication.
dessimation. The cross of lines of data in a movie window as the size of the fram is reduced. Lack of data for certain lines cuases undesirable artifacts during movie playback.
device. Any type of equipment, such as a printer, modem, monitor, disk drive, or mouse that can send or receive data.
device driver. A special program that controls a device. Specific to DOS, device drivers are required to control some devices (mouse, tape backup, CD-ROM drive, and so on).
DHCP. Dynamic Host Configuration Protocol (DHCP). A protocol for automatic TCP/IP configuration that provides static and dynamic address allocation and management.
dialog box. A window that pops up to ask for or display more information. It's a dialog between you and your software.
digital disk recorder. A recorder much like a viedotape recorder which uses large digital disk memories instead of tape. They can record and play back in single frame steps (with no pre-roll, since there is no tape involved), at variable speeds or at 30 fps. Digital disk recorders are available as both component and composite machines.
digital signature. A security technique consisting of attaching a code to a software component that identifies the vendor of the component.
digital video. A video signal represented by binary numbers describing a finite set of colors and luminance levels. In accordance with "CCIR 601," the international digital video standard for sampling, the conversion from analog to digital suffers virtually no loss.
DIN. Acronym for Deutsche Industrie Normal, a European standards organization.
DIP switch. DIP is an acronym for Dual-Inline Package. Mostly, you use DIP switches with modems to select COM ports or with printers to select options for output.
Direct Memory Access (DIM). A technique where information is transferred in a computer with the assistance of the microprocessor. For example, it's possible to transfer information between memory and an "intelligent" device, such as a hard drive, by simply telling a DMA chip to" move this data from memory here to disk driver there." The information is moved without slowing down the microprocessor.
directory. A list of files on a disk. It can also refer to a separate part of the disk where other files are stored (subdirectory). Every disk has at least one directory called the root directory. You can create other directories and label them so as to separate files that relate to different programs, data, and projects.
disk caching.Using the speed of solid state RAM to alleviate common data bottlenecks, the Macintosh operating system's RAM Cache control panel can allocate an area in RAM for storing the contents and results of a previous hard disk search. The cache provides an alternate area for the system to check before going to disk. During subsequent searches, if the system finds requested information in the cache, a disk search is not required, saving potential hard disk seek time and speeding up the retrieval process.
Disk First Aid. Disk First Aid is a utility included with all Macintosh computers which will allow you to check and repair some HFS file system errors. HFS is the file system used by most Macintosh hard drives and removable media such as Syquest, Zip, and Jaz drives.
Disk quota. A disk quota is the amount of space for file storage allotted to each user on a given computer.
dither pattern. The matrix of color or gray-scale values used to represent colors gray shades in a display system with a limited color palette.
dithering. A technique for alternating the values of adjacent dots or pixels to create the effect of intermediate values in printing color or displaying color on a computer screen, the technique of making adjacent dots or pixels different colors to give the illusion of a third color. For example, a printed field alternating cyan and yellow dots appears to be green. Dithering can give the effect of shades of gray on a black-and-white display, or more colors on a color display.
DNS (Domain Name System). A system for translating computer names into numeric Internet addresses. A static, hierarchical name service for TCP/IP hosts.
DNS name server. The servers that hold the DNS name database, and supply the I address that matches a DNS name in response to a request from DNS client.
docking base. See docking station.
docking station. A home for your laptop computer. Typically, a larger piece of equipment which you plug your laptop computer, often by sliding your laptop all the way into the larger piece of equipment. This extends your laptop's hardware, allowing you to use a larger screen and keyboard and other desktop features.
document. A file created by a word processor or desktop publisher, containing words or pictures.
domain. A grouping of computers. An organizational strategy in a database. But, most likely, a category of computers on the Internet. There are several popular domains: com, edu, gov, mil, gov, and net.
domain name. The unique name that identifies an Internet site. A given machine may have more than one domain name, but a given domain name points to only one machine.
dot pitch. The smallest size dot that a monitor can display, usually measured in millimeters (mm). Typical dot pitches for monitors are .41mm, .31mm, and .28mm. The smaller the dot pitch, the sharper the resolution on the monitor. Also used to describe the distance between two color dots of the same color on a color monitor.
dot space. The horizontal distance between dot centers. This distance depends on the character pitch in effect.
dots per inch. Sometimes abbreviated as DPI, dots per inch describes how sharp a printed image appears. The more dots per inch used, the sharper the image looks.
double-click. To press the mouse button twice in rapid succession without moving the mouse between clicks.
double-density disk. A floppy disk that stores twice as much information in the same amount of space as a single-density disk (which is no longer sold). Double-density disks are abbreviated as DD. A 5-1/4 inch double-density floppy disk can hold 360K of data. A 3-1/2 inch double-density floppy disk can hold 720K (800K for a Macintosh) of data.
down. When a piece of computer equipment temporarily stops working.
download. To copy files through a modem from a distant computer to the one you are working on.
downward compatible. The capability of software or hardware to work with earlier versions of the same software or hardware.
drag. To use the mouse for moving an object across the screen. First, you have to highlight (select) the object you want by pointing to it with the mouse. Then hold down the mouse button and move the mouse. This drags the object around.
drag and drop. Moving an object across the screen as a command. For example, you use a mouse to drag a document into a printer icon. This prints the document.
drop-down list box. A combination of two boxes. One box lets the user type information. The second box underneath lists names that the user can choose from.
drive setup. Drive Setup is a utility for formatting and partitioning your internal hard disk.
driver. A small piece of software that is installed into the operating system to allow it to use a specific device -- for example, the printer or network interface card (NIC).
DSOM. Short for Distributed System Object Model, a version of SOM that supports sharing binary objects across networks. DSOM is similar to Microsoft's competing standard called DCOM.
DTD. Short for document type definition, a type of file associated with SGML and XML documents that defines how the makrup tags should be interpreted by the application presenting the document. The HTML specification that defines who Web pages should be displayed by Web browsers is one example of a DTD. XML promises to expand the formatting capabilities of Web documents by supporting additional DTDs.
DTE. Short for Data Terminal Equipment, a device that controls data flowing to or from a computer. The term is most often used in reference to serial communications defined by the RS-232C standard. This standard defines the two ends of the communications channel as being a DTE and Data Communications Equipment (DCE) device. In practical terms, the DCE is usually a modem and the DTE is the computer itself, or more precisely, the computer's UART chip. For internal modems, the DCE and DTE are part of the same device.
dumb terminal. A unit consisting of a keyboard and video display connected to a main computer (such as a mainframe). Dumb terminals don't have disk drives or their own processors so they can't store files or do anything else on their own. Personal computers, on the other hand, can act as autonomous units which can be networked together.
dump. The copy information from one location to another without regard for its appearance or format. Often used for printing information that is temporarily useful.
duplex. A term used in telecommunications to describe how signals are send. Full duplex means that signals can be sent simultaneously back and forth. Half duplex means that signals can go only in one direction at a time.
dynamic allocation. The storage of information in the computer's memory (called the heap) while the program is running.
dynamic variable. A dynamic variable is a variable whose address is determined when the program is run. In contrast, a static variable has memory reserved for it at compilation time. (See also static variable).
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