Specifications

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Appendix A Glossary
Server System Infrastructure (SSI) A series
of power supply, motherboard, and chassis stan-
dards developed by Intel for servers.
ServerWorks A major developer of server
chipsets for use with Pentium III Xeon and
Xeon/Xeon MP processors. Now owned by
Broadcom.
Service Set Identifier (SSID) A unique identi-
fier of up to 32 characters that serves to differen-
tiate or “name” a wireless network.
servo The mechanism in a drive that enables the
head positioner to adjust continuously so that it is
precisely placed above a given cylinder in the drive.
servo data Magnetic markings written on disk
platters to guide the read/write heads in drives that
use voice-coil actuators.
session (single or multisession) A term used
in CD-ROM recording to describe a recording
event. In a single session, data is recorded on a
CD-ROM and an index is created. If additional
space is left on the disc, another session can be
used to record additional files along with another
index. Some older CD-ROM drives do not expect
additional recording sessions and therefore are
incapable of reading the additional session data on
the disc. The advent of Kodak’s Photo CD propelled
the desire for multisession CD-ROM XA (extended
architecture) drives.
Session Layer See OSI.
settling time The time required for read/write
heads to stop vibrating after they have been moved
to a new track.
shadow mask A thin screen full of holes that
adheres to the inside of a color CRT. The electron
beam is aimed through the holes in the mask onto
the phosphor dots. See also aperture grille.
shadow RAM A copy of a system’s slower-access
ROM BIOS placed in faster-access RAM, usually dur-
ing the startup or boot procedure. This setup
enables the system to access BIOS code without the
penalty of additional wait states required by the
slower ROM chips. Also called shadow ROM or ROM
shadowing.
shell The generic name of any user interface soft-
ware.
COMMAND.COM is the standard shell for DOS;
32-bit Windows uses the Windows Explorer as a
graphical shell and either
COMMAND.COM (Windows
9x/Me) or
CMD.EXE (Windows NT and later) as the
command-line shell.
shielded twisted-pair (STP) Unshielded
twisted-pair (UTP) network cabling with a metal
sheath or braid around it to reduce interference,
usually used in Token-Ring networks.
shock rating A rating (usually expressed in G
force units) of how much shock a disk drive can
sustain without damage. Usually two specifications
exist for a drive powered on or off.
signal-to-noise (S/N) ratio The strength of a
video or an audio signal in relation to interference
(noise). The higher the S/N ratio, the better the
quality of the signal. The latest high-end sound
cards have an S/N ratio of 100:1.
silicon The base material for computer chips. An
element, silicon (symbol Si) is contained in the
majority of rock and sand on earth and is the sec-
ond most abundant element on the planet next to
oxygen.
SIMD (single instruction multiple data)
The term used to describe the MMX and SSE
instructions added to the Intel processors. These
instructions can process matrixes consisting of mul-
tiple data elements with only a single instruction,
enabling more efficient processing of graphics and
sound data.
SIMM (single inline memory module) An
array of memory chips on a small PC board with a
single row of I/O contacts. SIMMs commonly have
30 or 72 connectors.
Simple Mail Transfer Protocol (SMTP) A
protocol for sending email messages between net-
work servers.
single-ended An electrical signaling method in
which a single line is referenced by a ground path
common to other signals. In a single-ended bus
intended for moderately long distances, commonly
one ground line exists between groups of signal
lines to provide some resistance to signal crosstalk.
Single-ended signals require only one driver or
receiver pin per signal, plus one ground pin per
group of signals. Single-ended signals are vulnera-
ble to common mode noise and crosstalk but are
much less expensive than differential signaling
methods.
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