Industry Terminology
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Daemon - Aprogram that runs in continuously in the background, or is activated by a particular event. The word daemon is Greek for "spirit or soul."
Daisy chain - To connect devices together in sequence with cables. For example, if four devices A,B,C and D are daisy chained, there will be a cable from A to B, a cable from B to C and a cable from C to D.
DASD – Direct Access Storage Device. Generic nomenclature for a storage peripheral that can respond directly to random requests for information. Usually refers to a disk drive.
DAT – Digital AudioTape. A digital recording technology that uses a helical scan method of recording on tracks that are diagonal to the edge of the tape. Media are similar to that used in audio recording.
Data Mart – A scaled-down version of a data warehouse that focuses on a particular subject area. Usually designed to support the unique business requirements of a specific department or business process.
Data Mining – A means of extracting previously unknown, actionable information from the growing base of accessible data in data warehouses using sophisticated, automated algorithms to discover hidden patterns, correlations and relationships.
Daughterboard – A board that attaches to another board (i.e. the motherboard).
Database – A file containing a collection of information organized into records, each of which contains labeled categories (fields).
Datagram - A self-contained data packet carrying its own address information so it can be independently routed from the source to the destination computer without reliance on earlier exchanges between the source and destination computer and the transporting network.
DDS – Digital Data Storage. Physical recording format adopted as a industry standard for DAT drives by ANSI and others.
Decompression – The expansion of compressed image files.
Dedicated line – A telephone or data line that is always available.
DES – Data Encryption Standard. U.S. government standard for data encryption.
DHCP - Dynamic Host Configuration Protocol. Windows NT Server software that assigns an IP address to each node in a network.
Dial-up line – A communication connection from your computer to a host computer over standard phone lines. Connection is established by dialing the host computer.
Differential - This form of SCSI uses a form of differential signaling, where each signal is actually carried by two different wires, each the mirror image of the other. So here, a "one" is represented by a positive voltage on one wire, and an equal but opposite negative voltage on another wire; a "zero" is electrical ground or zero voltage on both wires. This use of two conductors per signal makes the signal much more resilient and less likely to be corrupted. This allows the use of much longer cabling than single-ended SCSI.
Differential SCSI - See Differential.
Digital – Data or voltages consisting of discrete steps or levels.
Digital Certificates – Signed electronic documents that contain information uniquely identifying the user. They authenticate a Web browser’s access to a Web server.
Digital Transmission – Sound waves and other information are converted to binary computer code (a series of 0s and 1s). The information is sent in this format, then converted into its original format when it reaches its destination.
Digitizers – A machine that converts analog data into digital data on a computer.
Direct Connection – A permanent communication connection between your computer system and the Internet.
Disk Array – Two or more disks grouped together to appear as a single disk to the host system.
Disk Defragmenter – Arranges blocks of information for a file into adjacent blocks on the hard drive, which may significantly improve the file access time.
Disk Mirroring – The duplication of disks and controllers so that two access paths exist in case a failure occurs on one of them.
Distributed Filesystem – In a distributed filesystem, files can be accessed directly from any computer on a network. Access requests need not go through a single controlling server; file access control resides in any attached computer or storage device. Files appear to the user as if they were locally attached. The entire filesystem can appear as a single volume. All computers connected to the network, see the same image of all files within the filesystem and can share files. Converse of crossmounting.
Distribution Board - Printed circuit board with few or no active components.
DLT – Digital Linear Tape. A type of 1/2" wide magnetic tape used for backup.
DMA – Direct Memory Access. A means of handling data transfer between memory and a peripheral device that bypasses the central processing unit.
DMPP – Distributed Memory Parallel Processors. Massively Parallel Processing machines without shared memory capabilities. Also known as “loosely coupled.”
DNS - Domain Name System. The distributed name/address mechanism used in the Internet. A database system that translates an IP address into a domain name.
Domain Fault Tolerance – Elimination of single-point-of-failure across hosts and storage nodes on a network. In a distributed filesystem, in which disk operations are described at a file-level, RAID operations can be implemented across a logical unit rather than a single physical unit by striping across system boundaries.
Domain Name Server – Enable domain names to be resolved into numerical IP addresses.
DOS – Disk Operating System. The operating system used on IBM personal computers and compatible machines.
DoS – Denial-of-Service.
Download – To retrieve a file from another computer using a modem.
DPI – Dots Per Inch. A measure of resolution for a printer, scanner or monitor; referring to the number of dots in a one-inch line. The more dots per inch, the higher the resolution.
Driver – A piece of software that tells the computer how to operate an external device, such as a printer, hard disk, CD-ROM drive, or scanner.
DSP - Digital Signal Processor
DSS – Decision Support System. A data processing mode emphasizing user friendliness and ad hoc query, reporting and analysis capabilities. This mode is contrasted to online transaction processing, which focuses on low-cost, fast-response, predictably structured applications.
DTDS – Disaster Tolerant Disk Systems. New RAID Advisory Board classification for RAID storage systems. Replaces original numerical designations.
DRAM – Dynamic Random Access Memory. Computer memory chips that require electronic refresh cycles to preserve data stored for manipulation by logic chips.
Dump – Back-up of data.
DVD – Digital Video Disc (or Digital Versatile Disk). A removable optical data storage media primarily driven by the entertainment industry for distribution of feature-length movies.