| Term | Description |
| Default | That which is chosen by the Operating System or program if the user doesn't specify something different. E.g. default drive, default printer, default directory, etc.. |
| Defragment | Your computer can slow down when files become fragmented. This means that the clusters the file is stored in are not physically next to each other on the disk. The read/write heads have to travel further to read the file. By defragmenting, files are rewritten to the disk in contiguous clusters thus speeding up data retrieval. |
| Desktop | When an Operating System that uses a Graphical User Interface (GUI) is finished loading, the screen that is initially displayed is called the Desktop. When you run a program or open a folder it appears in a window on the Desktop. |
| Device Driver | Individual programs can access communication ports or expansion slots either directly or via the OS or BIOS. However, there is such a vast number of different devices available to hook up to your computer that it can't be expected to know how to use the features of all of them. Most devices are shipped with small programs that are loaded onto your hard drive and tell the computer how to communicate with that specific input/output device whether it be a modem, printer, video card, etc.. These small software programs are called Drivers and are specific to each make and model of the device it comes with. |
| Diffuse | A technique to create a gray-scale image. Pixel patterns aren't set; they change gradually throughout the image. |
| DIMM | Dual Inline Memory Module. A small printed circuit board with memory chips on it. These modules clip into sockets on the motherboard to make up your system RAM. They come in denominations of 16, 32, 64, and 128 MB. |
| DIP Switch | A small switch on a circuit board or some other device that holds configuration or setup information for that device. |
| Directory | A table made by the Operating System that contains file information such as file name, size, date created, and the file's beginning cluster number. |
| Display Adapter | An adapter board or interface card that fits into a slot on the motherboard and controls the video signal sent to the monitor. |
| Dither | To create a gray-scale image by using fixed patterns of black and white pixels to represent each shade of gray. Every time the image needs a particular shade of gray, the software uses the same pattern. |
| DLL | Dynamic Link Library. A file that contains several small programs or routines that are common to many programs such as opening a window or saving a file. These library files have a .dll extension. |
| DMA | Direct Memory Access is an electronic pathway or direct channel on which a device can bypass the CPU and send data directly to memory. A DMA channel is often one of the resources assigned when configuring an expansion card or device such as a sound card. |
| Documentation | Manuals, tutorials, and Help files that provide information that a user needs in order to use a computer system or software application. |
| Domain | On TCP/IP networks, such as the Internet, a domain is a group of connected computers. Domains are identified on the Internet by a two or three letter code. Some of the most common are: .com - commercial site, .edu - educational institution, .gov - government site, .net - network site, .org - non-profit or private organization, .ca - a Canadian site. A domain can also refer to a group of workstations on a network. There can be sub-domains within a domain. |
| Domain Name | An identifying name given to a system or group of computers on a network. For example, the domain name computerstuff.com indicates that the domain is a commercial site (.com) and that the sub-domain name is computerstuff. |
| Dot Pitch | The distance between pixels of the same color on a monitor screen. |
| DRAM | Dynamic Random Access Memory. The most common type of system RAM. It comes in several different flavors, EDO, FPM, SDRAM. It uses less space, less power, and is cheaper than static RAM, but it has to be refreshed every millisecond or it loses its information. |
| Driver | See Device Driver. |
| DriveSpace | DriveSpace is a Microsoft utility that is supposed to increase the amount of space on your hard drive. What it actually does is compress the files on your drive and create a single large file that contains all the compressed. The compression and decompression takes place in the background, unnoticeable to the user. |
| Dual Boot | The ability to boot your computer using one of two different operating systems. |
| Dual Voltage CPU | A Central Processing Unit that requires two different voltages, one for external functions and one for internal processing. |
| DVD | Digital Video Disk. A type of CD-ROM format that is faster and can hold more data than a regular CD-ROM. It still has the ability to read older CDs, but a DVD disk can hold more than 8 gigabytes (as opposed to 750 Mb) and can display full-motion picture videos. |
| Dynamic RAM | See DRAM. |