Safe area
The area in the center of a video frame that is sure to be displayed on all types of
receivers and monitors. Televisions and other monitors made at different times and by
different companies are slightly different in size and shape, and the outer edge of the
video frame (about 10 percent of the total picture) is not reproduced in the same way on
all sets.
Sampling
The process of taking measurable slices of an analog signal at periodic intervals.
Sampling can also refer to the process of obtaining values of a usually analog function by
making automatic measurements at periodic intervals. Sampling is a step in
analog-to-digital conversion, which comprises sampling, quantizing, and encoding.
Sampling rate
The rate at which slices are taken from analog signals in analog-to- digital
conversion. The sampling rate also determines the frequency at which points are recorded
in digitizing an image. Sampling errors can cause aliasing effects.
Saturated colors
Strong, bright colors (particularly reds and oranges) that do not reproduce well on
video, but tend to saturate the screen with color or bleed around the edges, producing a
garish, unclear image.
Scalability
The ability of a decoder to decode an ordered set of bitstreams to produce a
reconstructed sequence.
Scan lines
The parallel lines across a video screen, along which the scanning spot travels in
painting the video information that makes up a monitor picture. NTSC systems use 525 scan
lines to a screen; PAL systems use 625.
SCSI
Acronym for "Small Computer System Interface". Pronounced
"scuzzy." SCSI is a parallel interface standard used by Apple Macintosh
computers, PCs, and many UNIX systems for attaching peripheral devices to computers.
Nearly all Apple Macintosh computers, excluding only the earliest Macs and the recent
iMac, come with a SCSI port for attaching devices such as disk drives and printers. SCSI interfaces provide for faster data transmission rates (up
to 80 megabytes per second) than standard serial and parallel ports. In addition, you can
attach many devices to a single SCSI port, so that SCSI is really an I/O bus rather than
simply an interface.
Although SCSI is an ANSI standard, there are many variations of it, so two SCSI
interfaces may be incompatible. For example, SCSI supports several types of connectors.
The following varieties of SCSI are currently implemented:
- SCSI-1: Uses an 8-bit bus, and supports data rates of 4 MBps
- SCSI-2: Same as SCSI-1, but uses a 50-pin connector instead of a 25-pin connector, and
supports multiple devices. This is what most people mean when they refer to plain SCSI.
- Wide SCSI: Uses a wider cable (168 cable lines to 68 pins) to support 16-bit transfers.
- Fast SCSI: Uses an 8-bit bus, but doubles the clock rate to support data rates of 10
MBps.
- Fast Wide SCSI: Uses a 16-bit bus and supports data rates of 20 MBps.
- Ultra SCSI: Uses an 8-bit bus, and supports data rates of 20 MBps.
- SCSI-3: Uses a 16-bit bus and supports data rates of 40 MBps. Also called Ultra Wide
SCSI.
- Ultra2 SCSI: Uses an 8-bit bus and supports data rates of 40 MBps.
- Wide Ultra2 SCSI: Uses a 16-bit bus and supports data rates of 80 MBps.
SDRAM
Short for Synchronous DRAM, a new type of DRAM that can run at much
higher clock speeds than conventional memory. SDRAM actually synchronizes itself with the
CPU's bus and is capable of running at 100 MHz, about three times faster than conventional
FPM RAM, and about twice as fast EDO DRAM and BEDO DRAM. SDRAM is replacing EDO DRAM in
many newer computers. Today's fastest Pentium systems use CPU buses running at 100 MHz, so
SDRAM can keep up with them, though barely. Future PCs, however, are expected to have CPU
buses running at 200 MHz or faster. SDRAM is not expected to support these high speeds
which is why new memory technologies, such as RDRAM and SLDRAM, are being developed.
SECAM
format
Sequential Couleur A Memoire (sequential color with memory), the French color TV
system also adopted in Russia. The basis of operation is the sequential recording of
primary colors in alternate lines. The image format is 4:3, 625 lines, 50 Hz and 6-MHz
video bandwidth with a total 8 MHz of video channel width. See also NTSC, PAL.
Serial Port
A port, or interface, that can be used for serial communication, in which only 1 bit
is transmitted at a time. Most serial ports on personal computers conform to the RS-232C
or RS-422 standards. A serial port is a general-purpose interface that can be used for
almost any type of device, including modems, mice, and printers (although most printers
are connected to a parallel port).
SGRAM
Abbreviation of Synchronous Graphic Random Access Memory, a type of DRAM used
increasingly on video adapters and graphics accelerators. Like SDRAM, SGRAM can
synchronize itself with the CPU bus clock up to speeds of 100 MHz. In addition, SGRAM uses
several other techniques, such as masked writes and block writes, to
increase bandwidth for graphics-intensive functions. Unlike VRAM and WRAM, SGRAM is
single-ported. However, it can open two memory pages at once, which simulates the
dual-port nature of other video RAM technologies.
Side
information
Information in the bitstream necessary for controlling the decoder.
SIF (Standard Interchange format)
Format for exchanging video images of 240 lines with 352 pixels each for NTSC, and 288
ines by 352 pixels for PAL and SECAM. At the nominal field rates of 60 and 50 fields/sec,
the two formats have the same data rate.
Signal-to-noise (S/N) ratio
The strength of a video and/or audio signal in relation to interference (noise). The
higher the S/N ratio, the better the quality of the signal.
SIMM
Acronym for single in-line memory module, a small circuit board that can hold a
group of memory chips. Typically, SIMMs hold up 8 or 9 DRAM / SOJ chips. On PCs, the ninth
chip is often used for parity error checking. The bus from a SIMM to the actual memory
chips is 32 bits wide. A newer technology, called dual in-line memory module (DIMM),
provides a 64-bit bus. For modern Pentium microprocessors that have a 64-bit bus, you must
use either DIMMs or pairs of SIMMs.
SLDRAM
Short for SyncLink DRAM, a new type of memory being
developed by a consortium of computer manufacturers called the SyncLink Consortium. SLDRAM
is competing with Rambus memory (RDRAM) as the future PC memory architecture. But whereas
actual RDRAM chips are already in use on video boards and other devices, SLDRAM is still
on paper only. Moreover, Intel is backing RDRAM, which could mean that RDRAM will becoming
an important technology.
Slice
A series of macroblocks.
S.M.A.R.T.
Self-Monitoring, Analysis and Reporting Technology (S.M.A.R.T.) is an emerging
technology that provides near-term failure prediction for disc drives. When S.M.A.R.T. is
enabled, the drive monitors predetermined drive attributes that are susceptible to
degradation over time. If a failure is likely to occur, S.M.A.R.T. makes a status report
available so that the host can prompt the user to back up the data on the drive. Not all
failures are predictable. S.M.A.R.T. predictability is limited to the attributes the drive
can monitor.
SMPTE time code
An 80-bit standardized edit time code adopted by SMPTE, the Society of Motion Picture
and Television Engineers. See time code.
SO DIMM
Small Outline DIMM or SO DIMM is a type of memory commonly used in both notebook and
laptop computers. A Small Outline DIMM is like a 72-pin SIMM in a reduced-size package,
but with some important technical differences. The small outline DIMM and the both have 72
pins. However, it's the way the pins are arranged that differentiates these two types of
memory.
Software Modem
A modem implemented entirely in software. Software modems rely on the computer's
processor to modulate and demodulate signals.
SOJ
Short for Small-Outline J-lead, a type of chip module that
uses J-shaped pins that extend inwards. Unlike DIPs, which plug into holes on the circuit
board, an SOJ chip attaches directly to the circuit board's surface.
Spatial
scalability
A type of scalability in which an enhancement layer also uses predictions from pel
data derived from a lower layer without using motion vectors. The layers can have
different frame sizes, frame rates, or chroma formats.
Specular
Highlighting
Used to add extra color to polygons. This is typically used to add a color that gives
objects a shiny, wet, or metallic look.
SPID
Acronym for Service Profile Identifier, a number that identifies a specific ISDN
line. When you obtain ISDN service, your telephone company assigns a SPID to your line.
Part of the initialization procedure is to configure your ISDN terminal adapter to use
this SPID.
Most telephone companies in the U.S. use the Generic SPID Format, which is a 14-digit
number. The first 10 digits identify the telephone number, called the Directory Number
(DN). The remaining four digits identify a particular ISDN device, in the case where
multiple devices share the same Directory Number.
SRAM
Static RAM is faster and more less volatile than dynamic RAM, but it requires more power
and is more expensive hence used for Cache Memory on older main boards.
S T-506 Interface
An old standard interface for connecting hard disk drives to PCs. Newer standards,
such as enhanced IDE and SCSI, support faster data transfer rates. ST-506 is sometimes
referred to as MFM, which is the most prevalent encoding scheme used on ST-506 disk
drives. ST-506 also supports the RLL encoding format
Standard
A definition or format that has been approved by a recognized standards
organization or is accepted as a de facto standard by the industry. Standards exist for
programming languages, operating systems, data formats, communications protocols, and
electrical interfaces.
From a user's standpoint, standards are extremely important in the computer industry
because they allow the combination of products from different manufacturers to create a
customized system. Without standards, only hardware and software from the same company
could be used together. In addition, standard user interfaces can make it much easier to
learn how to use new applications.
Most official computer standards are set by one of the following organizations:
· ANSI (American National Standards Institute)
· ITU (International Telecommunication Union)
· IEEE (Institute of Electrical and Electronic Engineers)
· ISO (International Standards Organization)
· VESA (Video Electronics Standards Association)
IEEE sets standards for most types of electrical interfaces. Its most famous standard
is probably RS-232C, which defines an interface for serial communication. This is the
interface used by most modems, and a number of other devices, including display screens
and mice. IEEE is also responsible for designing floating-point data formats.
While IEEE is generally concerned with hardware, ANSI is primarily concerned with
software. ANSI has defined standards for a number of programming languages, including C,
COBOL, and FORTRAN.
ITU defines international standards, particularly communications protocols. It has
defined a number of standards, including V.22, V.32, V.34 and V.42, that specify protocols
for transmitting data over telephone lines.
In addition to standards approved by organizations, there are also de facto standards.
These are formats that have become standard simply because a large number of companies
have agreed to use them. They have not been formally approved as standards, but they are
standards nonetheless. PostScript is a good example of a de facto standard.
Start
codes
Unique 32-bit codes embedded in a coded bitstream. They are used for several purposes,
including identifying some of the structures in the coding syntax.
Stuffing (bits); stuffing (bytes)
Code words that can be inserted into a compressed bitstream and that are discarded in
the decoding process. Their purpose is to increase the bitrate of the stream.
S-VHS or Super VHS
A higher-quality extension of the VHS home videotape format, featuring higher
luminance and the ability to produce better copies.
S-video
Type of video signal used in the Hi8 and S-VHS videotape formats. S- video transmits
luminance and color portions separately, using multiple wires, thus avoiding the NTSC
encoding process and its inevitable loss of picture quality. Also known as Y/C video.
Sync-locked
The precise coincidence of two pulses, or signals, such as when the sync pulses of a
videotape recorder lock in with the sync pulses of a camera.
Stair-stepping
Jagged raster representation of diagonals or curves; corrected by anti- aliasing. |
