Glossary of terms - PC Based Instrumentation and Control - page 455

SCSI The SCSI (or 'Small Computer Systems Interface') provides a means of
interfacing up to eight peripheral devices, (such as hard disks, CD-ROM drives
and scanners) to a microcomputer system. With its roots in larger minicomputer
systems, SCSI tends to be more complex and expensive in comparison with
EIDE.

Sector The name given to a section of the circular track placed (during for-
matting) on a magnetic disk. Tracks are commonly divided into ten sectors (see
also Format ).

Segment 64 KB of contiguous data within memory. The starting address of
such a block of memory may be contained within one of the four segment
registers (DS, CS, SS, or ES).

Serial interface (serial port) A communications interface in which data is
transferred a bit at a time between a computer and a peripheral device, such
as a modem. In serial data transfer, a byte of data (i.e. 8 bits) is transmitted
by sending a stream of bits, one after another. Furthermore, when such data
is transmitted asynchronously (i.e. without a clock), additional bits must be
added for synchronization together with further bits for error (parity) checking
(if enabled).

Server A computer which provides network accessible services (e.g. hard
disk storage, printing, etc.).

Shell The name given to an item of software which provides the principal
user interface to a system. The DOS program COMMAND.COM provides a
simple DOS shell however later versions of MS-DOS and DR-DOS provide
much improved graphical shells (DOSSHELL and VIEWMAX, respectively).

Signal The information conveyed by an electrical quantity.

Signal level The relative magnitude of a signal when considered in relation
to an arbitrary reference (usually expressed in volts, V).

SIMM SIMMs (or 'Single In-line Memory Modules') are used to house the
DRAM chips used in all modern PCs. The modular packaging and standard pin
connections makes memory expansion very straightforward.

Slot A general term used to describe the sockets within a system (such as
AGP, PCI, ISA, RAM, etc.) which can be used to expand the system. Each slot
is designed to accept a printed circuit card. Note that the term 'slot' is also
used to describe the socket used to mount certain types of processor on the
motherboard (see Appendix F).

Software A series of computer instructions (i.e. a program).

Sound Card An interface card used to process audio data and provide audio
output to external speakers; also typically includes interfaces to a microphone,
game controller, and external MIDI devices.

Sub-directory A directory which contains details of a group of files and
which is itself contained within another directory (or within the root directory).