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Shugart Associates Systems Interface. The predecessor to SCSI.

Selector Channel. An intelligent bus used on the IBM 360 mainframe.

SCSI Configured AutoMatically. Method that automatically allocates SCSI Ids via software when SCAM compliant SCSI devices are attached.

A scanner is a device that converts visual information such as text or graphics into digital form for use in applications.

A device driver feature that lets the host adapter modify a transfer data pointer so that a single host adapter transfer can access many segments of memory. This minimizes interrupts and transfer overhead.

A version, or flavor, of UNIX developed by Santa Cruz Operations

Small computer System Interface. Pronounced "scuzzy" by much of the computer industry, SCSI is a system-level interface that provides what is essentially a complete expansion bus into which to plug peripherals. The original SCSI standard evolved from another interface called SASI, the Shugart Associates Standard Interface. This interface was developed in 1981 by hard disk pioneer hugart Associates working with NCR Corporation.   Together, they developed SCSI as an 8-bit parallel connection between host computers and disk drives. Later that year, the X3T9 committee of Amerian National Standards Institute used the SASI specification as the foundation for its work on a parallel interface stansard. That standard, now known as SCSI-1, was formally approved in 1986.

In 1991, a revision of SCSI was introduced to help fix some of the problems in mating SCSI devices, as well as to increase the speed of SCSI transfers. Referred to as SCSI-2, the new standard integrated a complete software-control system call Common Command Set with several optional hardware enhancements. These included the broadening of the 8-bit SCSI data bus to wide SCSI, which can use 16 or 32 data lines. These would double the effective peak transfer rate of the interface to 10MB or 20MB per second. Wide SCSI also expands the number of possible device connected to a single host adapter channel to 15.

Almost immediately after the SCSI-2 standard was approved, the industry began work on its successor SCSI-3, to refine the standard further. Rather than a single standard has become an umbrella that covers multitude of individual hardware and protocol standards.   Notably, it divorces software from hardware so that the Common Command Set and the various cabling systems go their separate directions. At that, SCSI itself becomes a command protocol and the various interconnection standards control how you wire your peripherals together. Each part of the SCSI-3 standard is published separately. Although many parts of the complete SCSI-3 system remain in draft form, other portions have been published as complete specification.

The original version of SCSI now is termed SCSI-1 to distinguish it from its heirs. As the progenitor SCSI-1 inspired the work that has led to today's SCSI standard.   SCSI-1 embraces only little more than the parallel wiring interface that serves as the basis for the current SPI design.

SCSI-1 devices need not understand the Common Command Set. As a consequence, early SCSI devices exhibited a variety of incompatibilities with one another. The only way of being certain that a given SCSI-1 device would work with another - including simple connections between host adapter and hard disk drive - was to buy a pair specifically matched by a peripheral manufacturer. Although many manufacturers later adapted the Common Command Set to their SCSI-1 devices, you have no assurance that a given SCSI-1 device will work with more modern SCSI implementations.

The second generation of SCSI; includes many improvements to SCSI-1, including Fast SCSI, Wide SCSI, and mandatory parity checking.

The third generation of SCSI; introduces Fast-20 and Fast-40 as improvements to the parallel bus. The standard also includes a number of specifications for high-speed serial bus architectures such as SSA, Fibre Channel, and IEEE 1394.

A chip on the host adapter that contains programs for communicating with the adapter and the bus.

A host adapter and one or more SCSI peripherals connected by cables in a linear chain configuration. The host adapter may exist anywhere on the chain, allowing connection of both internal and external SCSI devices. A system may have more than one SCSI bus by using multiple host adapters.

SCSI Device
Any device that conforms to the SCSI standard and is attached to the SCSI bus by a SCSI cable. This includes SCSI host adapters and SCSI peripherals.

A way to uniquely identify each SCSI device on the SCSI bus. Each SCSI bus has eight available SCSI IDs numbered 0 through 7 (or 0 through 15 for Wide SCSI). The host adapter usually gets ID 7 giving it priority to control the bus.

SCSI Device Management System. A Symbios Logic software product that manages SCSI system I/O.

SDRAM (Synchronous DRAM)
The SDRAM (Synchronous Dynamic Random Access Memory ) features a fully synchronous operation referenced to a positive edge clock whereby all operations are synchronized at a clock input which enables the coexistence of high performance and a simple user interface.  The SDRAM is ideally suited for supercomputers,workstations, high resolution graphic adapters, accelerators and other applications where an extremely large memory and bandwidth of memory are required and where a simple interface is needed.  

The major differences between SDRAM and conventional DRAM is synchronized operation, burst mode, and mode register. SDRAM uses a clock input for synchronization whereas the DRAM is an asynchronous memory module. DRAM uses two clocks, RAS# and CAS#. Each operation of DRAM is determined by the timing phase differences between the two clocks while each operation of SDRAM is determined by the reference of commands and operations referenced to a positive clock edge. The burst mode is a very high speed access mode utilizing an internal column address generator. Once a column address for the first access is set, following addresses are automatically generated by the internal column address counter.

The mode register receives the desired system conditions and in turn controls the SDRAM operation accordingly.

Simply put, you can say SDRAM takes memory access away from the CPU's control; internal registers in the chips accept the request, and let the CPU do something else while the data requested is assembled for the next time the CPU talks to the memory. As they work on their own clock cycle, the rest of the system can be clocked faster. There is a version optimized for video cards, and main memory for mainboard.

Sending bits individually, one after the other. See also parallel

Serial Interface
An interface between a computer and a serial device, such as a printer or modem, by which the computer sends single bits of information to the device, one after the other.

Serial Port
A port that transmits data a bit at a time, used for modems, mice, certain printers and communication devices.

A computer or device configuration.

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.

Containing a metal cover to keep out unwanted interference from the environment.   A shielded connector has a metal cover. A shielded cable has a foil wrapping or braided metal sleeve under the plastic covering.

Shrouded Header Connector
A device connector with a plastic guard around its perimeter. The shroud ensures that all the pins on a cable are plugged into the device. Shrouded connectors also have a notch on one side so that the cable can only be inserted in one direction.

Single In-line Memory Module. A pre-assembled unit of RAM chips that is easier to install than individual chips. A memory board must be designed specifically to use SIMMs. Many computers use SIMMs, though some now use DIMMs.

Single ended
"Normal" electrical signals. Uses open collector to the SCSI bus, [usually] survives wrong cable insertion. DIFFSENSE signal is used to detect connection of wrong type devices. The maximum length for SCSI-1 is a 6 meter cable with stubs of max 10cm allowed to connect a device to the main-cable. Most devices are single ended.

Single Ended SCSI
A hardware specification for connection SCSI devices. It references each SCSI signal to a common ground. This is the most common method (as opposed to differential SCSI which uses a separated ground for each signal).

The ability to perform only one process at a time. DOS is a single-tasking operating system.

Serial Line Internet Protocol. An implementation of the TCP/IP protocol to be used over serial lines (modems). Allows direct access to the internet over a modem. Compare with PPP, another such protocol.

Simple Mail Transfer Protocol. The protocol used to transfer E-mail between computers on the internet. It is a server to server protocol, so other protocols (like POP) are needed to transfer the E-mail to a client machine.

IBM's Systems Network Architecture. An early networking implementation.

Regular old, lick the stamp, seal the envelope, and then wait several days mail.   See also E-mail.

The entire set of programs, procedures, and related documentation associated with a computer system.

Electronics not utilizing vacuum tubes.

Sound card
An add-on card use to play and/or record audio.

Source code
Software instructions written as text in a high level programming language. It is readable by humans who know the language.

SPD (for SDRAM module)
Serial Presence Detect (SPD) is most like an ID detect for SDRAM module, it using a EEPROM component on DIMM module for storing module configuration information inside.

The Serial Presence Detect function is implemented using a 2048 bit EEPROM component.   This nonvolatile storage device contains data programmed by the DIMM manufacture that identifies the module type and various SDRAM organization and timing parameters.

Intel new 440BX chipset mainboard will detect your SDRAM module, if your module does not have SPD component, it will show a warning message at when system boot up.   However, it is harmless for your system and memory module.

To transfer data intended for a peripheral device (usually a printer) into temporary storage. From there the data can be transferred to the peripheral at a later time, without affecting or delaying the system as it performs other operations.

SRAM (Static RAM)
Static RAM is the fastest available, with a typical access time of 25 nanoseconds. Static RAM is more expensive and can only store a quarter of the data that DRAM is able to, as it uses two transistors to store one bit against DRAM's one, although it does retain it for as long as the chip is powered. The transistors are connected so that only one is either in or out at any time; whichever one is in stands for a 1 bit. Synchronous SRAM allows a faster data stream to pass through it; which is needed when used for cacheing on 90 and 100 MHz Pentium.

Serial Storage Architecture. A high-speed serial communication bus developed by IBM for sending commands, data and status signals between devices.

Able to operate without support.

A version of UNIX produced by Sun Microsystems for their Sun workstations.

Super Video Graphics Array. Specifications for video output that expanded the VGA specifications on IBM PC and compatible computers to more than 640x480 resolution, and more than 256 colors. There is not a single SuperVGA standard, so not all SuperVGA devices have compatible features.

Sustained speed
The rate at which data can be transferred continuously. See also burst speed.

Shortened form of synchronized. Events that happen at the same time.

Synchronous Data Transfer
One of the ways data is transferred over the SCSI bus. Transfers are clocked with fixed-frequency pulses. This is faster than asynchronous data transfer. Synchronous data transfers are negotiated between the SCSI host adapter and each SCSI device.

Synchronous SCSI
Rather then waiting for an ACK, devices that both support synchronous SCSI can send multiple bytes over the bus in the following way send data1 send data2 ... send data3 (max outstanding bytes) wait wait response1 reponse2 ...

This improves throughput, especially if you use long cables.(The time that a signal travels from one end of the cable to the other end of the cable IS relevant.)

Synchronous Transfer
A method of sending data that allows many bytes of data to be sent before acknowledgment is received from the target. Only data can be sent in synchronous mode.   Commands, messages, and status must be transmitted in asynchronous mode.

Synchronous transfer negotiation
The process of determining if a target is able to send/ receive data using synchronous transfers.

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 reduces the odds of SLDRAM becoming an important technology.

System BIOS
Controls the low level POST (Power On SelfTest), and basic operation of the CPU and computer system.


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