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D

DAT
Digital Audio Tape (DAT) is a compact, high capacity form of data storage, suitable for archiving or backing up large amounts of data.

Database
A database collects information into an electronic file, for example a list of customer addresses and associated orders. Each item is usually called a ‘record’ and the items can be sorted and accessed in many different ways.

Data compression
A process that reduces the amount of data needed to store or send a video or audio signal.

Data storage
Any type of information - words, figures, still or moving images, sound or music - can be coded into a single electronic form: digital. Once in digital format, all these types of material can be shared, copied, processed, indexed and transmitted from computer to computer, quickly and flexibly.

Dedicated server
A server which is used solely for use by one organisation. The server is leased and stored in the data center of the host company.

Desktop publishing
Desktop publishing (DTP) software was originally developed to allow computer users to create professional-looking newsletters, magazines and brochures, complete with pictures, diagrams and colour. Now that word-processing software can do most of these things, DTP software has become more of a tool for professional designers, though small companies often use DTP for producing newsletters and reports.

DHTML (Dynamic HyperText Markup Language)
DHTML refers to web pages that use a combination of HTML, JavaScript, and CSS to create features such as letting the user drag items around on the web page, some simple kinds of animation, and many more.

Digital certificate
An electronic statement issued by a certificate authority that verifies a company’s identity by validating that company’s public key.

Digital signature
A section of data appended to a message which authenticates the information. Signatures are encoded by the sender’s private key and can then verified by the sender’s public key. Any unauthorised changes to the file will be reported by an invalid signature for that file.

DNS
Domain Name System. The address mapping system used to match numeric internet addresses, e.g. 192.95.543.095 with www. web addresses.

Document management systems
The control of electronic documents, such as images, spreadsheets and word-processed files. A document management system is created by combining several types of software to control document identification, storage, retrieval, tracking, version control, workflow management and presentation. Good systems can create, use and control documents across different computers, software packages and company divisions.

Domain name
A company’s or individual’s permanent home on the web. Comes after the @ part of an email address or after www. Essentially, a domain name is your ‘real estate’ on the web.

Drive
The device in a computer that reads data from a disk.

DTP
See Desktop publishing.

DVD (digital versatile disk)
A high-density format for playing full motion video. It provides vast data storage capacity (currently 4.7Gb, more than 7 CDs). Although popular within the home market, DVDs can also be used to hold computer data.