Direct Access Storage Device (DASD): A storage device that can directly access data to be stored or retrieved, for example, a magnetic disk unit.
Direct Access: A method of storage where each storage position has a unique address and can be individually accessed in approximately the same period of time without having to search through other storage positions.
Direct Memory Access (DMA): A method whereby peripherals may transfer data into or out of main memory without the involvement of the CPU.
Distribution media format (DMF): A special read-only format for 3½ inch floppy disks that permits storage of 1.7 MB of data.
Dock: To insert or remove a device in a computer system.
Disk Operating System (DOS): An operating system for microcomputers in which all or part resides on a disk and must be loaded into the computer. It is a set of programs that controls and supervises the microcomputer’s hardware.
DOS Extender: A program, which allows a program to run in protected mode while still retaining access to real-mode MSDOS services.
DRAM (Dynamic Random Access Memory): RAM memory, which essentially consists of a tiny capacitor for each bit of memory. Since capacitors do not hold a charge indefinitely, DRAM must be constantly refreshed to avoid losing its contents. Also, the process of reading the contents of the memory are destructive, meaning extra time must be spent restoring the contents of memory addresses, which are accessed, so DRAM is slower than SRAM.
Dump: To copy the contents of all or part of a storage device, usually from an internal device, onto an external storage device.
DVD: Digital Versatile Disk. The optical disk storage that encompasses audio, video, and computer data.
EEPROM: A type of memory that can be erased and reprogrammed electrically without removing the chip from the circuit board.
Encryption: A way of making data indecipherable to protect it from unauthorized viewing or use.
EPROM: A type of memory that can be erased by removing it from the circuit and exposing the chip to ultraviolet light. It can then be reprogrammed.
Exception handling: An event that occurs as a program runs and that requires software outside the normal flow of control to be run.
Expanded Memory Specification: A specification devised by Lotus, Intel, and Microsoft for accessing more than one megabyte of memory by bank-switching additional memory into the one megabyte real mode address space.
Extended BIOS Data Area: A block of memory, typically the 1K at the top of conventional memory, which is used to store additional data for use by the BIOS which does not fit into the 256-byte data area at segment 0040h.
Extended File Control Block: A DOS File Control Block which has had an additional seven bytes prepended to permit control of file attributes (which are stored in the appendage).
Extended Memory: Memory beyond the one megabyte address which is available only on 80286 and higher machines. Except for a small portion (the High Memory Area) the extended memory is only accessible from protected mode.
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