Glossary of terms - PC Based Instrumentation and Control - page 448

Cluster A unit of space allocated on the surface of a disk. The number of
sectors which make up a cluster varies according to the DOS version and disk
type (see also Sector ).

Command An instruction (entered from the keyboard or contained within
a batch file) which will be recognized and executed by a system (see also
Batch file ).

Common A return path for a signal (often ground).

CONFIG.SYS A file which contains DOS configuration commands which
are used to configure the system at start-up. The CONFIG.SYS file specifies
device drivers which are loaded during initialization and which extend the func-
tionality of a system by allowing it to communicate with additional items of
hardware. See also Device Driver .

Controller A sub-system within a microcomputer which controls the flow of
data between the system and an I/O or storage device (e.g. a CRT controller,
hard disk controller, etc.). A controller will generally be based on one, or more,
programmable VLSI devices.

Coprocessor A second processor which shares the same instruction stream as
the main processor. The coprocessor handles specific tasks (e.g. mathematics)
which would otherwise be performed less efficiently (or not at all) by the main
processor. Note that maths coprocessors are no longer needed as all modern
processors have internal registers required for mathematics processing.

Cylinder The group of tracks which can be read from a hard disk at any
instant of time (i.e. without steeping the head in or out). In the case of a floppy
disk (where there are only two surfaces), each cylinder comprises two tracks. In
the case of a typical IDE hard disk, there may be two platters (i.e. four surfaces)
and thus four tracks will be present within each cylinder.

Daisy chain A method of connection in which signals move in a chained
fashion from one device to another. This form of connection is commonly used
with disk drives.

Data A general term used to describe numbers, letters, and symbols present
with a computer system. All such information is ultimately represented by
patterns of binary digits.

Data bus A highway (in the form of multiple electrical conductors) which
conveys data between the different elements within a microprocessor system.

Data file A file which contains data (rather than a program) and which are
used by applications such as spreadsheet and database applications. Note that
data may or may not be stored in directly readable ASCII form.

Device A hardware component such as a memory card, sound card, modem,
or graphics adapter.

Device driver A term used to describe memory resident software (speci-
fied in the CONFIG.SYS system file) which provides a means of interfacing
specialized hardware (e.g. a graphics adapter). See CONFIG.SYS .