Glossary 5
boot sector
The part of the boot block that contains the operating system loader, a program that
starts by itself and loads the operating system.
bps
Bits per second. The number of bits of data that can be transmitted in one second.
Because data compression schemes enable more than one bit per voltage transition,
bps is equivalent to baud only if no compression is used.
buffer
A place, especially in RAM, for the temporary storage of data for the purpose of
speeding up an operation such as printing or drive access. Data from a buffer is
available more quickly than data from where the buffer got it. Typically buffers get
data before it is needed so it is ready quickly when needed. Similar to cache.
burst mode
When a device seizes control of the bus, sends data, then relinquishes control of the
bus. Any time a device sends data without interruption instead of taking turns with
other devices.
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. See “write-back” and “write-
through.”
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