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Datagram
Datagram is a block of data that is "smart" enough (actually, which carries enough information) to travel
from one Internet site to another without having to rely on earlier exchanges between the source and destination
computers.
Datagram is a self-contained, independent entity of data carrying sufficient information to be routed from the
source to the destination computer without reliance on earlier exchanges between this source and destination computer
and the transporting network. The term is used in several well-known communication protocols, including the User
Datagram Protocol and AppleTalk.
A very similar term, packet, is used in the Internet Protocol and other protocols related to the Internet.
A datagram or packet needs to be self-contained without reliance on earlier exchanges because there is no connection
of fixed duration between the two communicating points as there is, for example, in most voice telephone conversations
(this kind of protocol is referred to as connectionless).
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D Channel (Delta Channel)
A 16-kbps channel used to signal the telephone-company computer to make calls, put them on hold, and activate features
such as Conference Calling and Call Forwarding. It also receives information about incoming calls, as in Caller
ID.
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DCE (Data Communications Equipment)
Devices providing the functions required to establish, maintain, and terminate a data-transmission connection-for
example, a modem.
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DDS (Dataphone® Digital Service)
A communications service from AT&T in which data is transmitted in digital rather than analog form.
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Dedicated Line
A communications line that is used solely for computer connections. If you buy an additional phone line for your
modem, that's a dedicated line. There are other types of dedicated lines (such as T3 and T1 that are used for larger
network entities).
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Default image hyperlink
In an image map, the hyperlink to follow when a user clicks in an area where there are no hotspots on the image.
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Definition
The HTML style of the second paragraph of a pair of paragraphs composing a definition list entry. The first paragraph
in the pair is the term.
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Definition list
Much like an actual key used for locking and re-opening doors, DEKs are used for the encryption and decoding of
message text, sometimes in the form of a digital signature.
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DEK (Data Encryption Key)
Used for the encryption of message text and for the computation of message integrity checks (signatures).
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Defragment
Defragmenting consolidates each existing file and the free space into a contiguous group of sectors. Access speed
will be improved due to reduced seeking. A nearly-full disk system will fragment more quickly. A disk should be
defragmented before fragmenting reaches 10%. So, defragmenting is to rearrange the way that files are organized
on a disk such that the data comprising each file is stored to contiguous disk clusters. When files are fragmented,
disk performance worsens.
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Demo
Demoware is limited evaluation software that has some of its features disabled. This software usually allows the
use of a fair amount of features to entice a user to purchase the full product.
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DES (Data Encryption Standard)
A standardized encryption method widely used on the Internet.
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DHTML (Dynamic HTML)
Instructions written in HTML that enable Web pages to react to user input and produce content that changes each
time it is viewed. With dynamic HTML coding, Web pages are created "on the fly", as the information is
delivered to your desktop. There are many technologies for producing dynamic HTML, including CGI scripts, Server-Side
Includes (SSI), cookies, Java, JavaScript, Cold Fusion and ActiveX.
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Dialup
A widely-used method of accessing the Internet. A dialup connection uses regular phone lines to connect one computer
to another via modem.
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Digital
Transmission mode in which data is encoded as either a binary one (1) or zero (0). Compare to analog.
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DIN
DIN is a plug and socket connector consisting of a circular pattern of pins in a metal sleeve. This type of connector
is commonly seen on keyboards.
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Directory
Directory is an index into the files on your disk. It acts as a hierarchy, and you will see them represented in
Windows looking like manila folders.
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DirectX
Microsoft DirectX is a group of technologies designed by Microsoft to make Windows-based computers an ideal platform
for running and displaying applications rich in multimedia elements such as full-color graphics, video, 3-D animation,
and surround sound. Built directly into the Microsoft Windows family of operating systems, DirectX is an integral
part of Windows 98, Windows ME, Windows XP and Windows 2000, as well as Microsoft Internet Explorer.Microsoft DirectX
is a set of application programming interfaces (APIs) that allow applications to gain access directly to a system’s
multimedia hardware. The DirectX APIs included in Windows 98 can be broken down into the following components:
DirectDraw®, a 2-D graphics interface, supports accelerated animation techniques by providing direct
access to bitmaps in off-screen display memory as well as extremely fast access to the blitting and buffer-flipping
capabilities of a computer's video adapter.
DirectSound® provides an interface between applications and an audio adapter’s sound mixing, playback,
and capture capabilities.
Direct3D®, a 3-D graphics interface, supports the 3D-rendering functionality built into modern display
adapters.
DirectPlay® allows for easy connectivity of games over a modem link or network.
DirectInput® provides functionality to process input from joysticks, gamepads, keyboards, mice, Human
Interface Device (HID) devices, and force feedback devices. Although DirectInput is similar to Windows 98 input
components, it provides advanced joystick input capabilities for games and scalability for future Windows hardware
input APIs and drivers.
DirectAnimation makes it possible to have titles that combine different types of media, such as images, 3-D objects,
sounds, movies, and text, where any or all the media types can be animated and respond to user input. DirectAnimation
enables multimedia content on Web pages, on your desktop, and in standalone titles.
DirectShow, formerly known as ActiveMovie, provides support for a Digital Video Disk (DVD) Navigator/Splitter,
proxy filters for video and audio streams, a video mixer, a video renderer, and an audio renderer.
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DLL (Dynamic Link Library)
A Windows file containing executable code that can be shared by running applications. DLLs also enable applications
to share other resources necessary to perform particular functions.
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DMA (Direct Memory Access)
DMA is a fast way of transferring data within a computer. Most devices require a dedicated DMA channel, so the
number of DMA channels that are available may limit the number of peripherals that can be installed.
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DNS (Domain Name System)
The DNS is a static, hierarchical name service used with TCP/IP hosts, and is housed on a number of servers on
the Internet. Basically, it maintains a database for figuring out and finding (or resolving) host names and IP
addresses on the Internet. This allows users to specify remote computers by host names rather than numerical IP
addresses The advantage of the DNS is that you don't have to remember numerical IP addresses for all the Internet
sites you want to access.
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Domain
1. ICT Domain is a set of network resources (shared files, applications, printers and other devices) for a group
of users in Windows NT / Windows 2000 / Windows 2003 and Windows 2008 environments. In the ICT domain, a Domain
Controller (DC) has all the user accounts which are allowed to exercise sets of rules over these shared resources.
All the users have to join in to the domain and then login to gain access to the resources. Resources may be located
on a number of different servers in the network, depending on the domain server environment model.
2. Domain is also a "logical" region of the Internet. People sometimes refer to them loosely as "sites."
Generally, a domain corresponds to an IP address or an area on a host.
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DOS (Disk Operating System)
Usually used as an abbreviation for MS-DOS, a micro-computer operating system developed by Microsoft.
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Download
To download files is to transfer them from a server to a local machine. Opposite of upload.
To copy data (usualy an entire file) from a main source to a perepherial device. The term is often used to
describe the process of copying a file from an online service to one's own computer.
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DRAM (Dynamic Random Access Memory)
DRAM is a type of memory used in a PC for the main memory (such as stated "256 Mbytes of RAM"). "Dynamic"
refers to the memory's memory of storage - basically storing the charge on a capacitor. Specialized types of DRAM
(such as EDO memory) have been developed to work with today's faster processors. See also SDRAM.
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Driver
Driver is a program designed to interface a particular piece of hardware to an operating system or other software.
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Drop-down menu field
A form field that presents a list of selections in drop-down menu style. A drop-down menu form field can be configured
to permit the selection of many fields or a single field.
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DSL (Digital Subscriber Line)
The root of all xDSL services. It consists of two 64-kbps bearer (B) channels and one 16-kbps (D) channel (2B+D).
These channels are bundled together into a 128-kbps pipeline for simultaneous transmission of voice, data, fax,
or video signals.
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DSU (Digital Service Unit)
The interface between a user's data terminal device (DTE) and a digital data service, usually via a CSU. Converts
an RS-232C or other terminal interface to a DSX-1 interface.
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DSX-1 Interface
The CSU interface to which a T1 line is attached. This can be either a DB15 female or an RJ-48C female connector.
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Dumb Terminal
Dumb Terminal refers to devices that are designed to communicate exclusively with a host (main frame) computer.
It receives all screen layouts from the host computer and sends all keyboard entry to the host. It cannot function
without the host computer.
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DTE (Data Terminal Equipment)
Devices acting as data source, data sink, or both.
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DVI (Digital Visual Interface)
A high-performance interface between a computer and a display device that uses TMDS (Transition-Minimized Differential
Signaling) for improved video signal accuracy. DVI-D is a digital-only connector; DVI-I integrates both digital
and analog connections.
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