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DAC or D-A converter
DB-9,DB-15,DB-19,DB-25,DB-37,and DB-50
Information in a form suitable for processing by a computer, such as the digital representation of text, numbers, graphic images, or sounds.
data area
In DOS, that part of a floppy disk or hard disk that is available for use after the boot record, partition table, root directory, and file allocation table have been established by the formatting program. This area is the largest part of a disk and is where programs and data files are located.
data bits
In asynchronous transmissions, the bits that actually comprise the data; usually 7 or 8 data bits make up the data word.
data compression
Any method of encoding data so that it occupies less space than in its original form. Many different mathematical techniques can be used, but the overall purpose is to compress the data so that it can be stored, retrieved, or transmitted more efficiently. Data compression is used in facsimile and many other forms of data transmission, CD-ROM publishing, still image and video image manipulation, and database management systems.
data encoding scheme
The method used by a disk controller to store digital information onto a hard disk or floppy disk. Common encoding schemes used in the PC world include modified frequency modulation (MFM) encoding, run-length limited (RLL) encoding, and advanced run-length limited (ARLL) encoding.
Data Encryption Standard (DES)
A standard method of encryptiong and decrypting data, developed by the U.S. National Bureau of Standards.

DES is a block of cipher that works by a combination of transposition and substitution, and was developed after years of work at IBM, rigorously tested by the National Security Agency, and finally accepted as being free of any mathematical or statistical weaknesses. This meaning, that it is impossible to break the system using statistical frequency tables or to work the algorithm backwards using standard mathematical methods. DES has remained unbroken despite years of use; it completely randomizes the information so that it is impossible to determine the encryption key even if some of the original text is known. DES is used by the federal government and most banks and money-transfer systems to protect all sensitive computer information.

data-link layer
The second of seven layers of the International Standards Organization's Open Systems Interconnection (ISO/OSI) model for computer-to-computer communications. The data-link layer validates the integrity of the flow of data from one node to another by synchronizing blocks of data, and by controlling the flow of data.
data packet
In networking, a unit of information transmitted as a discrete entity from one node on the netwok to another. More specifically, in packet-switching networks, a packet is a transmission unit of a fixed maximum length that contains a header, a set of data, and error control information.
data rate
The speed of a data transfer process, normally expressed in bits per second or bytes per second.
data set ready (DSR)
A hardware signal defined by the RS-232-C standard to indicate that the device is ready.
Data Terminal Equipment (DTE)
In communications, any device, such as a terminal or a computer, connected to a communications channel or public network.
data terminal ready(DTR)
A hardware signal defined by the RS-232-C standard to indicate that the computer is ready to accept a transmission.
data transfer rate
The speed at which a disk drive can transfer information from the drive to the processor, usually measured in megabits or megabytes per second.
data type
DB(data bus) connector
Any of several types of cable connectors used for parallel or serial cables. The number after DB represents how many pins the connector has;i.e., DB-25 has twenty-five pins.
DCE (Data Communications Equipment)
In communications, any device that connects a computer or terminal to a communications channel or public network, usually a modem.
DCI (Display Control Interface)
A device-driver specification from Intel and Microsoft intended to speed up video playback in Microsoft Windows. Multimedia applications and programs that manage digital video benefit from the usage of DCI.
A quarter-inch tape minicartridge used in some tape backup systems with a capacity of up to 250MB when some form of data compression is used.
Display data channel.
The Plug and Play baseline for monitors. The communications channel between a monitor and the display adapter to which it is connected. This channel provides a method for the monitor to convey its identity to the display adapter.
DEC Alpha
A 64-bit microprocessor from Digital Equipment Corporation, introduced in 1992. It is a superscalar design, which allows the processor to execute more than one instruction per clock cycle.
decibel (dB)
One tenth of a bel, a unit of measurement common in electronics that quantifies the loudness or strength of a signal.
To reverse the procedure conducted by compression software, and thereby return compressed data to its original size and condition.
dedicated line
A communications circuit used for one specific purpose.
Deferred procedure call
Method used in Windows NTŪ and Windows 2000 for event scheduling.
The process or reorganizing and rewriting files so that they occupy one large continuous area on your hard disk rather than several smaller areas.
Any uitility program that rewrites all the parts of a file into contiguous clusters on a hard disk.
demand paging
A common form of virtual memory management where pages of information are read into memory from disk only when required by the program.
The degree of darkness of an image. Also, the percent of screen used in an image.
Any circuit that performs a specific function, such as a parallel port.
Device Bay
An industry specification that defines a mechanism for both peripheral devices and system bays that allows adding and upgrading PC peripheral devices without opening the chassis.
the requirement that a specific hardware component be present for a program to work.
Device driver
A small program that allows a computer to communicate with and control a device.Note: In DOS, device drivers are loaded by the DEVICE or DEVICEHIGH commands in CONFIG.SYS.
device ID
A unique ASCII string for the device created by enumerators to identify a hardware device and used to cross-reference data about the device stored in the registry. Distinguishes each logical device and bus from all others on the system.
Device-independent bitmap
A file format designed to ensure that bitmap graphics created using one application can be loaded and displayed in another application exactly the way they appeared in the originating application.
device node
The basic data structure for a given device, built by the Configuration Manager. Device nodes are built into memory at system startup for each device and enumerator. Each device node contains information about the device, such as currently assigned resources.
device object
A kernel-mode-only object type used to represent a physical, logical, or virtual device whose driver has been loaded into the system.
Describes any device that represents values in the form of binary digits.
digital audio
Analog sound waves stored in a digital form; each digital audio file can be decomposed into a series of samples.
digital audio tape(DAT)
DAT. A method of recording information in digital form on a small audio tape cassette.DATs can be used as backup media.
Digital Signal Processor (DSP)
A specialized high-speed chip, used for data manipulation in sound cards, communications adapters, video and image manipulation, and other data-acquisition processes where speed is essential.
digital-to-analog converter
DAC or D-A converter. a device that converts discrete digital information into a continuously varying analog signal.
Digital Video Interactive (DVI)
A proprietary technique from Intel Corporation used to store highly compressed, full-motion video information onto compact discs.
DIN connector
A German standard used mostly for audio applications. DIN connectors are used for keyboards, PS/2 style mice, MIDI, and Apple printer attachments. DIN connectors are round.
DIP switch
A small switch used to select the operating mode of a device, mounted as a dual in-line package. DIP switches can be either sliding or rocker switches, and are often grouped together for convenience. They are used on printed circuit boards, dot-matrix printers, modems, and other peripherals.
direct access storage device(DASD)
A storage device such as a hard disk, whose data can be accessed directly, without having to read all the preceding data.
direct memory access (DMA)
A method of transferring information directly from a mass-storage device such as a hard disk or from an adapter card in memory (or vice versa), without the information passing through the processor. because the processor is not involved in the transfer, direct memory access is usually very fast.
DMA transfers are controlled by a special chip known as a DMA controller; 8237A is used in most PCs. Generally, most PCs use two of these chips to provide 8 DMA channels numbered 0 through 7; channel 4 is used to connect-or cascade-the two controllers together. Channels 0 thru- 3 are 8-bit channels, and can manage up to 64K of data in a single DMA operation; channels 5 thru 7 transfer data 16 bits at a time and can manage up to 128K of data. Channel 3 is reserved for the floppy disk drive controller, and channel 5 is used by the hard-disk controller in PS/2 systems.
disk cache
An area of computer memory where datat is temporarily stored on its way to or from a disk. A disk cache program can significantly speed up most disk operations. DOS contains the disk cache driver SMARTDRV.SYS, and OS/2 provides CACHE if you are using the high performance file system, or DISKCACHE if you are using the file allocation table system. Disk cache programs are also available from other third party sources.
disk controller
The electronic circuitry that controls and manages the operation of floppy or hard disks installed in the computer.
disk drive
A peripheral storage device that reads and writes magnetic or optical disks. Three common types of disk drives are :floppy-disk drive, hard-disk drives, and compact disc drives.
disk duplexing
In networking, a fault-tolerant technique that writes the same information simultaneously onto two different hard disks, using tow different disk controllers to provide greater redundancy..This is done so that in the event of one disk or disk controller failing, information from the other system can be used to continue operations.
disk I/O controller
Also HDC. A special-purpose chip and circuitry that directs and controls reading from and writing to a computer's disk drive.
disk mirroring
In networking, a fault-tolerant technique that writes the same information simultaneously onto two different hard disks using the same disk controller. In the event of one disk failing, information from the other can be used to continue operations
disk optimizer
A utility program that rearranges files and directories on a disk for optimum performance.
distributed processing
A computer system in which processing is performed by several separate computers linked by a communications network. The term often refers to any computer system supported by a network, but more properly refers to a system in which each computer is chosen to handle a specific workload, and the network supports the system as a whole.
A special format for 3.5" floppy disks that permits storing 1.68 MB of data on a standard 1.44-MB disk. This enables Microsoft to provide more software on fewer disks. For example, with a product like Office 95, users will have to install eight fewer disks as a result of DMF disk compression.
DMI (Desktop Management Interface)
A standard method of identifying PC hardware and software components automatically, without input from the user. A framework created by the Distributed Management Task Force (DMTF). DMTF specifications define industry-standard interfaces for instrumentation providers and management applications.
DNS (Domain Name System)
The method used when naming Internet host computers, and the directory services used when looking up those names. Each of these host names corresponds to a long decimal number known as the IP address. These domain names are much easier to remember than the long IP addresses.
The general category that a computer on the Internet belongs to. The most common high-level domains are:
  1. Acronym for Disk Operating System, an operating system orignally developed by Microsoft for the IBM PC. DOS exists in two very similar versions; MS-DOS and PC-DOS.
  2. A DOS CONFIG.SYS command that loads the operating system into conventional memory,extended memory, or into upper memory blocks on Intel computers.
To insert a portable computer into a base unit. Cold docking means the computer must begin from a power-off state and restart before docking. Hot docking means the computer can be docked while running at full power. See also warm docking.
docking station
The base computer unit into which a user can insert a portable computer, expanding it to a desktop equivalent. A typical docking station provides drive bays, expansion slots, all the ports on an equivalent desktop computer, and AC power.
A physical device, attached to a PC's I/O port, that adds hardware capabilities.
Kernel-mode code used either to control or emulate a hardware device.
driver stack
Device objects that forward IRPs to other device objects. Stacking always occurs from the bottom up and is torn down from the top.
Double-Sided Double-Density usually refers to 360k 5.25" floppy disks, or 720k 3.5" disks. These disks are obsolete and not recommended for new PCs, which can use the high-density disks.
Digital Signal 3(DS3) is an international transmission standard that uses pulse-code modulation and time-division multiplexing to achieve a data rate of 44.736 Mbps and provide full T3 connectivity; it is often used for ATM formats. E3 is the European counterpart that has a rate of 34.368 Mbps.
Dual boot
Allows the computer to boot to two different operating systems (DOS & UNIX, for example).
dual in-line package (DIP)
A standard housing constructed of hard plastic commonly used to hold an integrated circuit. The circuit's leads are connected to two parallel rows of pins designed to fit snugly into a socket; these pins may also be soldered directly to a printed -circuit board.
dumb terminal
A combination of keyboard and screen that has no local computing power, used to input information to a large, remote computer, often a minicomputer or a mainframe. This remote computer provides all the processing power for the system.
In asynchronous transmissions, the ability to transmit and receive on the same channel at the same time; also referred to as full duplex. Half-duplex channels can transmit only or receive only.
Optical disk storage that encompasses audio, video, and computer data.
dynamic detection
The process by which a system can detect that a new device has been added or removed from the PC. This process allows the operating system and applications to immediately begin using the added devices or stop using the removed devices without rebooting the system.
dynamic link library (DLL)
A program module that contains executable code and data that can be used by application programs, or even by other DLLs, in performing a specific task.
dynamic RAM(DRAM)
A common type of computer memory that uses capacitors and transistors storing electrical charges to represent memory states. These capacitors lose their electrical charge, and so need to be refreshed every millisecond, during which time they cannot be read by the processor.

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