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dialog box: 1) A box requesting information. Typically it contains a
combination of buttons, lists and text-entry boxes. 2) A box con
taining a message. It may tell you that a process has completed
successfully. Alternatively, it may be a warning that the computer
cannot do what you asked or that obeying your instructions may
destroy data. This second type of dialog box is also called a mes
sage box.
DIMM: Dual Inline Memory Module. A unit of RAM used for mem
ory expansion.
direct current (DC): Electric current that flows in one direction. This
type of power is usually supplied by batteries.
Direct Memory Access (DMA): A dedicated channel which bypasses
the Central Processing Unit (CPU) and enables a device to access
memory directly. If two devices use the same DMA channel, the
data required by one device overwrites the data required by the
other—this is one type of hardware conflict. To resolve the con
flict, you must reassign one of the devices to a vacant DMA chan
nel.
directory: See folder.
disable: To turn a computer option off. In a menu or dialog box, a dis
abled option appears dim (or "grayed out") and clicking it has no
effect. See also enable.
disk: A circular platter that can store computer information. In the case
of the hard disk and diskettes, the platter is coated with a magnetic
material and enclosed inside a protective case. The CD-ROM or
DVD-ROM, however, is an optical, not a magnetic, storage
medium. See also CD-ROM, DVD-ROM, hard disk, diskette.
disk cache: A technique that speeds up processing. Each time your
application receives data from a disk, a special program stores the
data in a reserved area of memory (RAM). When the application
next requests data, it looks for it first in the disk cache. Since read
ing from and writing to memory is quicker than using a disk drive,
this can considerably improve system performance.
Part I: Getting To Know Your Computer
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