8
Glossary
bus
A parallel electrical pathway on the system board, connecting
and shared by the parts of a computer system (especially the
CPU, its support circuitry, memory, and expansion cards), used
for transmitting data or electrical power from one device to
another. Typically the lines in a bus are dedicated to specific
functions, such as control lines, address lines, and data lines.
Different bus architectures have different numbers and
arrangements of these lines, and different names (for example,
ISA, PCI). The most useful way of distinguishing bus
architectures is by the number of simultaneous data bits they
can carry. The ISA is a 16-bit bus, while PCI is a 32-bit bus.
bus master
The ability of an expansion card to control the bus without
needing intervention from the CPU.
byte
Group of eight contiguous bits. Frequently written as an eight-
digit binary number or a two-digit hexadecimal number. One
letter of the alphabet in ASCII code takes one byte.
C
cache
A special block of fast memory used for temporary storage of
frequently used data for quick retrieval. A memory cache,
sometimes called a cache store or RAM cache, is a portion of
memory made of high-speed static RAM (SRAM) instead of
the slower and cheaper dynamic RAM (DRAM) used for
system memory. Memory caching is effective because most
programs access the same data or instructions over and over.
By keeping as much of this information as possible in SRAM,
the computer avoids accessing the slower DRAM. The
strategies for determining which information should be kept in
the cache constitute some of the more interesting problems in
computer science. See “write-back” and “write-through.”
