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| D | Data Buffer :
A section of high speed memory that is used by many devices to hold data during input or output operations. This allows slower devices like hard drives to effectively transfer information onto a faster bus. The data is read from the hard drive and stored into the buffer. Once the buffer is full the data is transferred as a block of information, therefor using the full speed of the bus. The same works in reverse.
Daughter Board :
An add-on card which is connected to a device to expand the capabilities of said device. Most sound cards and video cards have connectors for daughter boards, to add extra mixing effects or video capture.
Depth Cueing :
This creates distance by reducing colour and hue the farther away an object is from the viewpoint.
Depth Of Field :
Refers to the distance at which 3D objects are drawn in the distance. Closer objects are rendered more carefully and precisely than objects further way, which can be blurred and less precise. The scale at which object's precision is based on the depth of field setting.
Dial-Up Networking / Dial-up Connection :
A remote connection to another network; like the Internet; that uses a standard phone line. This connection requires a telephone number to be dialed, making it any connection that uses a standard modem.
Die :
The physical piece of silicon that has all of the transistors and circuits.
Digital :
Consisting of only on and off signals, represented as binary (1's and 0's) information. This is opposed to analogue, were a value is specified according to a signal scale.
Digital Signal Processor (DSP) :
An ASIC which is designed to do simple functions at incredibly high speeds. These chips are most commonly used for frequency generation and reception, such as in digital phones and wireless networking. Speeds of over 3GHz is not uncommon for these processors.
Digital Subscriber Line (DSL) :
A highspeed broadband connection that uses the unused frequencies of a phone line. Maximum speeds are dependent on the length of wire between the DSL modem and telephone switching office.
Digital to Analog Converter (DAC) :
A device or computer chip which converts digital information to analog information.
Digital Video Interface (DVI) :
A digital connection used for LCD monitors. Because LCD screens operate with a digital signal, it saves the digital to analog, and then back to digital conversion a regular monitor connecter would use. This produces a sharper image on digital monitors.
Direct Memory Access (DMA) :
The ability of a device to access system memory without having the CPU prefetch and send it the information.
Direct Rambus Dynamic Access Memory (DRDRAM) :
It is a high speed memory technology that uses multiple high speed channels for DRAM, rather then one large slow one. It currently has the highest effective bandwidth, but also a high latency.
DirectX (Direct3D, DirectDraw, DirectSound) :
A collection of API's written by Microsoft which are used as a common platform for 3D and multimedia applications. This collection currently includes different API for each aspect; DirectSound for sound, DirectDraw for 2D and sprite based graphics, Direct3D for 3D graphics, DirectPlay for networking, and DirectInput to handle user input. Instead of programs having to program the low level functions for each of these, they can pass the job off to these preprogramed APIs. DirectX is also a standard to which hardware is build. If hardware is compatible with DirectX, and programs are compatible with DirectX, than the software and hardware will be compatible, and so the software will be able to take advantages of low level features otherwise unaccessible.
DirectX Texture Compression (DXTC) :
A lossy standard designed by S3 for DirectX which allows for realtime compression/decompression at rates of up 6:1. DXTC is implemented though hardware.
Disk Operating System (DOS) :
The oldest PC operating system. It was single threaded and never allowed much flexibility in memory management or low level functions. Windows 98 still uses DOS to load, but newer operating systems like Windows 2000 and Windows ME have removed it.
Dithering :
This is used to reduce the colour banding that results with low colour depths, like 8-bit and 16-bit. Instead of having direct gradients with colours gradually changing in colour, each colour pixel is randomly diffused creating an overall gradient.
Domain Name System (DNS) :
The matching of host names to IPs.
Dongle :
A device which has to be attached to a computer in order to run specific software products. It is used as a copyright protection feature, and is usually attached to a serial or parallel port. Only ever used with really expensive software.
Dual Inline Memory Module :
Simply a SIMM which has twice the modules creating a 64-bit interface.
Double Buffering :
This is when video cards use two separate buffers for video display. A front buffer is where the image is stored which is drawn on screen during every refresh. The back buffer is where the next frame is being assembled. When the image in the back buffer is assembled, it is copied to the front buffer where it will be displayed until it is overwritten by the next complete frame. Without double buffering, the image in the back buffer will be drawn on screen whether it is complete or not, creating a flickering effect.
Double Data Rate (DDR) :
Any bus or device which is capable of receiving data twice per clock, once on the rising edge and once on the falling edge.
Double Precision Floating Point :
A double sized floating point defined by 64-bits instead of the regular 32-bits. This is usually only used with scientific calculations because it takes twice as long for a processor to calculate.
Downsample :
the process of making a file smaller by removing extra extraneous information.
Driver :
The software layer between the hardware device and the operating system. Drivers tell the operation system or API what features a device has, and how to use them.
Dual Inline Package Switch (DIP Switch) :
A small physical switch comparable to a jumper.
Dual Tone, Multi-Frequency (DTMF) :
The assigning of values to specific frequencies, like with a touch tone phone. Each tone created by the receiver when dialing is assigned to a specific number, so that the telephone office knows which number is being dialed.
Dynamic Host Control Protocol (DHCP) :
The network protocol which is used when computers do not know their IP address. A computer without an IP sends a request to a DHCP and the server sends back the needed information to the computer on how establish a TCP/IP connection. This if used with dial-up Internet connections because each user of the service doesn't need their unique IP address because all of the users won't be connected at the same time. When an IP isn't in use, it can be used by another computer.
Dynamic Linked Library (DLL) :
An compiled binary which is an extension to an executable. Used to store extra code and work in a modular design.
Dynamic Random Access Memory (DRAM) :
Memory which has to be periodically refreshed to retain data. Available in either FP, EDO, BEDO, SD, or DDRSD configurations. It doesn't suffer the capacities as SRAM, allowing most chips to contain up to 64MB, opposed to SRAM's 4MB limitation.
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