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DATABASE - A collection of information organized for easy retrieval. Databases are organized in to a hierarchy of files, records, and fields. A file is a group of related information, such as personal information about a group of employees. Information about a particular employee (name, SS#, address, etc.) is stored in a record. A RECORD is a collection of related data items called FIELDS. For example, a company's employee FILE stores information about each employee in a single RECORD consisting of FIELDS for the employee's name, Social Security number, and address.
DDE - Dynamic Data Exchange. DDE is a form of interprocess communication implemented in multitasking operating systems such as Microsoft Windows and OS/2. Information, commands, and status information can be exchanged between two or more programs if they support DDE and are executing simultaneously. For example, a spreadsheet with a DDE link to a communications program could keep its stock prices current with the trading information received over the communications channel. An exchange of data in DDE is called a conversation and an application can participate simultaneously in multiple DDE conversations with any number of other applications. A conversation is organized around three conceptual descriptors: service, topic, and item.
DEBUG - locate and remove errors in a program or computer.
DEFAULT - a value or state assumed to be true by the computer unless contrary instructions are given.
DES - Data Encryption Standard. The Data Encryption Standard was designated in 1977 by the National Institute of Standards and Technology as the official method of protecting unclassified computer data both in agencies of the federal government and commercially. The DES was originally developed by IBM researchers.
DESKTOP PUBLISHING (DTP) - One of the fastest-growing applications in personal computing. Desktop Publishing software offers a relatively inexpensive way for a PC to generate typeset-quality text and graphics.
DEVICE DRIVER - A program loaded by the CONFIG.SYS file or AUTOEXEC.BAT file that controls devices such as a mouse or CD-ROM drive.
DIALOG BOX - An on-screen box found in graphical user interfaces which provides users with information and explains limited options.
DIGITAL - There are two main ways of doing things electronically, analog or digital. The digital method is to consider a circuit either on or off, a signal as either present or absent, with no levels in between. Electronic circuits using the digital mode are simple to design and non-critical in operation. The all-or-nothing nature of digital circuits make them immune to drift and distortion, and their simplicity makes them easy to manufacture in large quantity. Digitizing is defined as transforming a signal or piece of information into digital form.
DIGITIZING TABLET - A digitizing tablet is an input device for obtaining accurate graphics input. It is connected to the microcomputer with a cable and includes some type of pen-like pointing device called a transducer. The tablet has a flat surface with a defined space, or active drawing area, where the operator can place a map, a drawing, or a menu overlay. A pointing device is then used to pinpoint areas within the work space, and the tablet sends coordinate data to the CAD application program. While a mouse reports a relative position based on its last known position, a digitizer returns an absolute location regardless of the last known position of the transducer. Compared to a mouse, a digitizing tablet is more precise and can take samples faster. Also, because the stylus and fixed surface provide for a more natural drawing motion, artists and designers prefer digitizing tablets.
DIN connector - DIN is an abbreviation for Deutshe Industrie Norm. The DIN connector is a multiple pin connector conforming to the specification of the German national standards organization. On most IBM-compatible microcomputers, 5-pin DIN connectors are used to connect the keyboard to the motherboard of the system unit. An 8-pin DIN connector is used as the serial port connector on Macintosh computers. IBM PS/2 computers use a 6-pin DW connector to connect the keyboard and the pointing device.
DIP switch - DIP is an acronym for Dual In-Line Package. Printed circuit boards and peripheral devices are often equipped with a bank of DIP switches. There are two styles; slide switches and rocker switches. In both cases, the switch positions can be set on or off with a ball point pen or some other pointed object. These hardware switches allow for a variety of operating conditions to be set before the board or device is put into use.
DIRECTORY - A directory is an area on a disk for storing files. Directories consist of files and/or subdirectories. A directory listing will show the names of files and subdirectories subordinate to that directory along with file sizes, creation dates and times. Each formatted disk contains a main directory also called the root directory. In DOS, the most common hard disk root directory is referred to as "C:\" or just "C:".
DIRECTORY TREE - A way of organizing data into a hierarchical structure, beginning with a root directory and branching into subdirectories and files.
DISK CACHE - A disk cache is a software technique of speeding data access times. Copies of recently accessed disk sectors are stored in memory to a reserved area called cache RAM. When the executing program or the operating system requests to read a sector from the disk, the disk caching software checks to see if the sector is stored in cache RAM. If it is, the sector is retrieved from RAM and returned; no disk access is required. If the desired sector is not in cache RAM, the software reads the requested sector from the disk, stores it in cache RAM, and returns it to the program. When the info is found in the cache, it's a hit. When the info must be retrieved from the disk, it's a miss. Some disk caching programs also check for sector writes.
DISK DRIVE - the mechanical apparatus, consisting of a shaft and motor for rotating the disk, and a magnetizing head for reading/writing the disk.
DISKETTE - A flat piece of flexible plastic covered with a magnetic coating which is used to store data (also called a FLOPPY DISKETTE). The former standard for diskette size was 5.25 inch; they were truly flexible, hence the descriptor "floppy". Newer 3.5 inch diskettes are encased in a hard plastic coating (which makes them more durable).
DLLs - Dynamically Linked Libraries. DLLs are libraries of object files or executable code modules available to programmers writing code for the Microsoft Windows operating environment. Functions and procedures written in languages like Pascal and C can be compiled and the object file stored in a DLL. These modules can be loaded at run time, and then unloaded when the code is no longer needed. The use of DLLs allows for a high degree of customization. If a particular development language doesn't support a required function, it could be written in another language and made available through the DLL.
DMA - After a sector of data has been read from a disk drive into the disk controller's onboard buffer it must be moved into the computer. This is done with a process known as DMA or (Direct Memory Access). The transfer of data takes place directly along an input/output channel at high speed between memory and the device. The CPU only initiates the transfer on a DMA request and therefore is not involved.
DNS - Domain Name System. The database for translating IP addresses in verbal format into numeric format.
DOS - Disk Operating System. Software that translates the user's commands and allows application programs to interact with the computer's hardware. DOS supplies a file management system for disk input and output.
DOS EXTENDER - A superset, or addition to DOS, added to programs that allows the programs to run in EXTENDED MEMORY.
DOS PROMPT - The signal that DOS is awaiting your command. The prompt is usually displayed as the current drive letter and the greater-than symbol (>). Thus C> is a DOS prompt with C representing the hard drive as the CURRENT DRIVE (i.e. C:\>, A:>, or C:\DOS>). Other operating systems use prompts, of course, each with its own format.
DOT MATRIX PRINTER (DMP) - A type of printer that employs a movable printhead with pins, or wires, that shoot out and strike a ribbon. Each strike of a single pin creates a dot on the paper. Letters are formed as a pattern, or matrix, of dots. The most common are 9 or 24 pin printers.
DOWN TIME - when the computer isn't working.
DRAM - Dynamic Random Access Memory. It is a kind of memory chip in which data is stored capacitively and which must be energized or recharged hundreds of times a second or the data will be lost. While DRAM is being refreshed, it cannot be read by the processor. If the processor attempts to read the DRAM while it is being refreshed, one or more wait states occur. DRAMs offer high bit densities, low cost, input/output compatibility with TTL levels, and speed compatibility with most microprocessors. The operational speed of DRAM chips is measured in nanoseconds, such as 100, 80, and 70ns.
DRIVER - A software program that allows the operating system (like DOS or UNIX) to work with a specific hardware device like a printer, a mouse, or trackball. (See also DEVICE DRIVER)
DUMP - transfer a block of the contents of memory to some output device or disk. A CORE DUMP is transfer of the entire contents of memory to the hard drive as a result of a program crash.
DVORAK KEYBOARD - Designed by August Dvorak, patented in 1936, approved by ANSI in 1982, the Dvorak keyboard provides increased speed and comfort and reduces the rate of errors by placing the most frequently used letters in the center for use by the strongest fingers. In this fashion, finger motions and awkward strokes are reduced by over 90 percent in comparison with the familiar QWERTY Keyboard. The Dvorak keyboard has the five vowel keys, AOEUI, together under the left hand in the center row, and the five most frequently used consonants, DHTNS, under the fingers of the right hand. Some businesses are requiring their keyboard personnel to use this system. Also, several computer companies are now manufacturing keyboards with a switch that will change from one keyboard design to the other. There are also TSRs with keyboard macros to convert your present keyboard to the Dvorak style.
--E--
ECHO - the display of characters sent to a file or to a remote computer on the screen of the originating computer.
EGA - An Enhanced Graphics Adapter is an IBM video display adapter that can be used with color and enhanced color displays. It also provides a monochrome graphics mode. In color it can produce characters in a dot box of 8 by 14 pixels when used with an enhanced color display. The EGA operates at a horizontal scan rate of 21.85 MHz, and can display 16 colors from a palette of 64 at a resolution of 640 by 350 pixels. To be fully EGA compatible, a video display monitor must have a bandwidth of at least 16 MHz.
EISA - The Industry Standard Architecture (ISA) for IBM-compatible microcomputers defines the use of the data bus and the 8-bit and 16-bit expansion slots on the PC-XT and PC-AT models. EISA is the Extended ISA. With an EISA bus, 8- or 16-bit add-in boards based on the Industry Standard Architecture (ISA) can be fitted to the new machines.
EPS - Encapsulated PostScript - The best quality graphics are vector graphics in which the image is made up of lines, curves, and filled regions rather than a series of data points as in bit-mapped graphics. EPS refers to a condensed graphics file containing actual PostScript language in a special format. EPS files can become quite large, and some contain a bit-mapped image of the graphic so that if the output is sent to a non-PostScript printer, the bit-mapped image is used. To get the best results, however, EPS files should be output on a PostScript device.
EXPANDED MEMORY (EMS) - Memory outside the one (1) megabyte (MB) limit of DOS that is accessed in revolving blocks.
EXPANSION CARDS - Electronic circuit cards that fit into slots on the main circuit board inside the case of the computer. Expansion cards are used to add such items as modems, sound capability, ports, etc. to a PC.
EXPANSION SLOT - A socket inside the computer case that is designed to hold expansion cards.
EXTENDED MEMORY (XMS) - Linear memory extending beyond the one (1) megabyte (MB) limit of DOS. Extended memory is only available on 80286-and-above machines; it is off-limits to 8088s and 8086s. (The distinction between conventional, expanded, and extended memory does not exist on a UNIX machine.)