<
architecture> One of the sets of conductors (wires, PCB
tracks or connections in an
integrated circuit) connecting
the various
functional units in a computer. There are
busses both within the
CPU and connecting it to external
memory and
peripheral devices. The data
bus, address
bus
and control signals, despite their names, really constitute a
single
bus since each is useless without the others.
The width of the data
bus, i.e. the number of parallel
connectors, and its
clock rate determine its data rate (the
number of
bytes per second which it can carry). This is one
of the factors limiting a computer's performance. Most
current
microprocessors have 32-bit busses both internally
and externally. 100 or 133
megahertz bus clock rates are
common. The
bus clock is typically slower than the processor
clock.
Some processors have internal busses which are wider than
their external busses (usually twice the width) since the
width of the internal
bus affects the speed of all operations
and has less effect on the overall system cost than the width
of the external
bus.
Various
bus designs have been used in the
PC, including
ISA,
EISA,
Micro Channel,
VL-bus and
PCI. Other
peripheral busses are NuBus, TURBOchannel, VMEbus, MULTIBUS and
STD
bus.
Some
networks are implemented as a
bus at the {physical
layer}, e.g.
Ethernet - a one-bit
bus operating at 10 (or
later 100)
megabits per second.
The term is almost certainly derived from the electrical
engineering term "
bus bar" - a substantial, rigid power supply
conductor to which several connections are made. This was
once written "'
bus bar" as it was a contraction of "omnibus
bar" - a connection bar "for all", by analogy with the
passenger omnibus - a conveyance "for all".
More on derivation (http://foldoc.org/pub/misc/omnibus.html).
(2000-03-20)