computer bus

bus
computer 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 (http://foldoc.org/pub/misc/omnibus.html).

   (2000-03-20)