bus
<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.
(2000-03-20)
Nearby terms:
Burst Extended Data Out DRAM « burst page « Burst
Static Random Access Memory « bus » bus error
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