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Lexikon

bus

hitecture> One of the sets of conductors (wires, PCB tracks or connections in an href="module.php?name=Lexikon&file=search&eid=1&query=integrated circuit">integrated circuit) connecting the various href="module.php?name=Lexikon&file=search&eid=1&query=functional units">functional units in a computer. There are busses both within the href="module.php?name=Lexikon&file=search&eid=1&query=CPU">CPU and connecting it to external memory and href="module.php?name=Lexikon&file=search&eid=1&query=peripheral">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 href="module.php?name=Lexikon&file=search&eid=1&query=clock rate">clock rate determine its data rate (the number of href="module.php?name=Lexikon&file=search&eid=1&query=bytes">bytes per second which it can carry). This is one of the factors limiting a computer' s performance. Most current href="module.php?name=Lexikon&file=search&eid=1&query=microprocessors">microprocessors have 32-bit busses both internally and externally. 100 or 133 href="module.php?name=Lexikon&file=search&eid=1&query=megahertz">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 href="module.php?name=Lexikon&file=search&eid=1&query=PC">PC, including href="module.php?name=Lexikon&file=search&eid=1&query=ISA">ISA, href="module.php?name=Lexikon&file=search&eid=1&query=EISA">EISA, href="module.php?name=Lexikon&file=search&eid=1&query=Micro Channel">Micro Channel, href="module.php?name=Lexikon&file=search&eid=1&query=VL-bus">VL-bus and href="module.php?name=Lexikon&file=search&eid=1&query=PCI">PCI. Other peripheral busses are NuBus, TURBOchannel, VMEbus, MULTIBUS and STD bus. Some href="module.php?name=Lexikon&file=search&eid=1&query=networks">networks are implemented as a href="module.php?name=Lexikon&file=search&eid=1&query=bus">bus at the {physical layer}, e.g. {Ethernet} - a one-bit bus operating at 10 (or later 100) href="module.php?name=Lexikon&file=search&eid=1&query=megabits per second">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://www.foldoc.org/pub/omnibus.html)}. (2000-03-20)

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