On a microcomputer, the bus is usually called anexpansion busbecause its design determines the degree to which the minimum configuration of the system can be expanded with regard to memory, processing speed, graphics capability, and peripheral support. The expansion bus is the collection of wires, paths, connectors, and controllers responsible for distributing the data and instructions from the microprocessor to the peripheral expansion cards.Slotsconnected to the bus provide places to plug those cards in, and the bus then provides a mechanism for communicating with them.
In modern designs the expansion bus is not normally the same bus that the CPU uses to access MAIN MEMORY, as the contention this would cause could slow the whole system down. Expansion cards may also be allowed to use DIRECT MEMORY ACCESS to avoid involving the CPU in most of their memory operations.
Examples of expansion buses include the ISA BUS and PCI BUS in the PC world, the VMEBUS for UNIX systems and the NUBUS for the Apple MACINTOSH.