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DASD :
Direct Access Storage Device. IBM nomenclature for a storage
peripheral that can respond directly to random requests for
information; usually denotes a disk drive.
Data Base :
Refer to DBMS.
Data Dictionary :
A repository of information about data, such as its meaning,
relationships to other data, origin, usage and format. The
dictionary assists company management, database
administrators, systems analysts and location programmers in
effectively planning, controlling and evaluating the
collections, storage and use of data. A data dictionary
manages data categories such as alias, data elements, data
records, data structure, data store, data models, data flows,
data relationships, processes, functions, dynamics, size,
frequency, resource consumption and other user-defined
attributes.
Data Model :
The logical data structure developed during the logical
database design process is a data model or entity model . It
is also a description of the structural properties that define
all entities represented in a database and all the
relationships that exist among them.
Data Set Ready (DSR) :
Signal emitted by a modem indicating that it is ready to
exchange signals with the computer.
Data Terminal Ready (DTR) :
Signal emitted by a computer indicating that it is ready to
exchange signals with the modem.
DBA :
Database Administrator. The person responsible for managing
data at a logical level, namely data definitions, data
policies and data security.
DB/DC :
Database/Data Communication. This acronym refers to IBM's
collection of transaction managers and database managers,
e.g., Customer Information Control System, Information
Management System, Database-2 and SQL/DS.
DBMS :
Database Management System. A complete software facility for
building, maintaining and generating reports from a database.
It has evolved along three generic forms :
-
hierarchical DBMS (1960s) - records were organized in a
pyramid-like structure, with each record linked to a parent
-
network DBMS(1970s) - records could have many parents, with
embedded pointers indicating the physical location of all
related records in a file
-
relational DBMS (1980s) - records were conceptually held in
tables, similar in concept to a spreadsheet. Relationships
between the data entities were kept separate from itself.
Data manipulation created new tables, called views.
DCE :
Distributed Computing Environment. DCE is the Open Software
Foundation's solution to the problems of interconnectivity in
a heterogeneous computing environment, standards and security.
The DCE is composed of two sets of services : fundamental
services from Digital Equipment Corp., Hewlett-Packard, the
Massachusetts Institute of Technology, and Siemens, and
data-sharing services from Microsoft, Sun Microsystems and
Transarc. DCE integrates remote procedure calls, presentation
services, a naming directory, security, threads (sequential
flow of control similar to task) , time services (to
synchronize clocks in a DCE) and a distributed file system.
Default value :
Implicitly used value, when no explicit value has been used by
the user.
Dell Computer :
US PC manufacturer, among the 5 largest in this business
Density Measure of the
quantity of data that can be registered by longitudinal inch
on a mass storage unit such as a disk drive.
Dial UP :
The process of, or the equipment or facilities involved in,
establishing a temporary connection via the switched network.
Dialog box :
Rectangle displayed on the screen after selecting certain menu
options. Dialog boxes propose complementary options in
relation with the requested operation.
Digerati :
The digital version of literati, it is a reference to a vague
cloud of people seen to be knowledgeable, hip, or otherwise
in-the-know in regards to the digital revolution.
Digital (DEC) :
Digital Equipment Corporation, Maynard, California. Third
worldwide computer manufacturer, re-centered
on processors business, and more especially the 64-bit Alpha
chip
Digitizers :
A purely graphical input device - i.e., a computer-aided
design/computer-aided manufacturing system device used in
computer-aided engineering for converting locations into
storable electronic impulses - with a surface on which a
location or point is selected and then automatically converted
into a digital X-Y co-ordinate suitable for transmission to a
computer.
DIP :
Dual In-Line Package. Standard format for integrated circuits
manufacturing, in which silicon-engraved microcircuits are
embedded in a rectangular plastic or ceramic container, and
connected on each long side of the circuit through pins
directed towards the bottom.
Disk Mirroring :
The duplication of disks and controllers so that two access
paths exist in case a failure occurs on one of them.
Diskette Medium used to store data. The magnetic support is
protected by a plastic cartridge. The capacity of 3.5 inch
diskettes is 1.4 MB (in High Density mode).
Display :
Unit such as CRT or LCD allowing the user to read information
produced by the computer.
Distributed Database :
A database whose objects (tables, views, columns and files)
reside on more than one system in a network, and can be
accessed or updated from any system in the network.
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.
DMA :
Direct Memory Access. Process allowing to exchange data
between the central storage and an I/O device without passing
through the CPU.
DME :
Distributed Management Environment. From the Open Software
Foundation, DME will result in architectures and services that
will simplify systems management applications across multiple
platforms. DME includes such tasks as backup/restore, printing
services, software installations, software distribution and
user management. A more global initiative allows organizations
to have a consistent approach to managing their systems.
DNS :
(Domain Name System) The Domain Name System is the system that
translates Internet domain names into IP numbers.
A "DNS Server" is a server that performs this kind of
translation.
Domain Name :
The unique name that identifies an Internet site. Domain Names
always have 2 or more parts, separated by dots. The part on
the left is the most specific, and the part on the right is
the most general. A given machine may have more than one
Domain Name but a given Domain Name points to only one
machine. For example, the domain names:
www.discoverscs.com
can all refer to the same machine, but each domain name can
refer to no more than one machine.
Usually, all of the machines on a given Network will have the
same thing as the right-hand portion of their Domain Names (discoverscs.com
in the examples above). It is also possible for a Domain Name
to exist but not be connected to an actual machine. This is
often done so that a group or business can have an Internet
e-mail address without having to establish a real Internet
site. In these cases, some real Internet machine must handle
the mail on behalf of the listed Domain Name.
DOS :
Disk Operating System (or Dirty Operating System ?). Developed
by Microsoft, it became a standard when bought by IBM, in
1981.
Double click :
Operation consisting in pressing quickly twice the mouse
button without moving the mouse
Download :
Transferring data (usually a file) from a another computer to
the computer you are are using. The opposite of upload.
Downsizing :
The process of moving computing work to a smaller computer.
More generally, it is often applied to applications that might
otherwise have been implemented on a big computer, being
brought up on a small computer.
DPI :
Dots Per Inch. A measurement of resolution ; e.g., the number
of pixels per inch on a cathode-ray tube display.
DRAM :
Dynamic Random Access Memory. Type of main storage that
require a permanent rewrite (each some milli-seconds), as
opposed to Static RAM. In 1995, access time is in the range
50-80 nano-seconds.
DSL :
(Digital Subscriber Line) A method for moving data over
regular phone lines. A DSL circuit is much faster than a
regular phone connection, and the wires coming into the
subscriber's premises are the same (copper) wires used for
regular phone service. A DSL circuit must be configured to
connect two specific locations, similar to a leased line
(however a DSL circuit is not a leased line.
A common configuration of DSL allows downloads at speeds of up
to 1.544 megabits (not megabytes) per second, and uploads at
speeds of 128 kilobits per second. This arrangement is called
ADSL: Asymmetric Digital Subscriber Line.
Another common configuration is symmetrical: 384 Kilobits per
second in both directions.
In theory ADSL allows download speeds of up to 9 megabits per
second and upload speeds of up to 640 kilobits per second.
DSL is now a popular alternative to Leased Lines and ISDN,
being faster than ISDN and less costly than traditional Leased
Lines. |
