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Satellite Computer - A computer that is connected to another computer, with which it interacts over a communications link. As its name indicates, a satellite computer is of lesser “stature” than the main, or host computer; the host controls either the satellite itself or the tasks the satellite performs.

Scrap - An application or system file maintained for storage of document data that has been marked for movement, copying, or excision.

Scratchpad - A temporary storage area used for calculations, data, and other work in progress. In reference to a microprocessor, scratchpad refers to a special high-speed memory circuit used to hold small items of data for rapid retrieval.

Secondary Storage - Any data storage medium other than a computer’s random access memory – typically, tapes or disk.

Security Kernel - An operating-system kernel that is protected from unauthorized use.

Serial Communications - The transmission of information between computers or between computers and peripheral devices one bit at a time over a single line. Serial communications can be synchronous (controlled by some time standard such as a clock) or asynchronous (managed by the exchange of control signals that govern the flow of information). An important aspect of serial communications – and a potential source of difficulty – is that both sender and receiver must use the same baud rate, parity, and control information.

Settling Time - The time required for a disk drive’s read/write head to stabilize over a new site after being moved from another position over the disk.

Sign Bit - The most significant (leftmost) bit of a number field, usually set to 1 if the number is negative. When an 8-bit value is added to a 16-bit value using signed arithmetic, the microprocessor propagates the sign bit through the high order half of the 16-bit register holding the 8-bit value in a process called sign extension or sign propagation.

SIMM - Abbreviation for single in-line memory module, a small circuit board designed to accommodate surface-mount memory chips. See the illustration. SIMMs use less board space and are more compact than more conventional memory-mounting hardware.

Single-Board Computer - A computer that occupies single circuit board, usually with no facility for installing additional circuit boards. Industrial machinery often uses an on-board computer to control its operation; this computer is usually a single-board computer.

Small Model - A memory model of the Intel 80*86 processor family. The small model allows only 64 kilobytes (KB) for code and only 64 KB for data.

Smart Terminal - A terminal that contains a microprocessor and random access memory (RAM) and that does some rudimentary processing without intervention from the host computer. Generally, a smart terminal can limit keyboard input to particular fields of the display and can perform some input validation (such as restricting input to numbers).