Busses

 The busses are the nervous system of the computer. They connect the various functional block of the computer both internally and externally. Within a computer, a bus is a grouping of similar signals. Thus, your Pentium processor has a 32-bit address bus and a 32-bit data bus. In terms of the bus structure, this means that there are two bundles of 32 wires with each bundle containing 32 individual signals, but with a common function. We’ll discuss busses much more thoroughly in a later lesson.The typical computer has three busses: One for memory addresses, one for data and one for status (housekeeping and control). There are also industry standard busses such as PCI, ISA, AGP, PC-105, VXI and so forth. Since the signal definitions and timing requirements for these industry-standard busses are carefully controlled by the standards association that maintains them, hardware devices from different manufacturers can generally be expected to work properly and interchange-ably. Some busses are quite simple—only one wire—but the signals sent down that wire are quite complex and require special hardware and standard protocols to understand it. Examples of these types of busses are the universal serial bus (USB), the small computer system interface bus (SCSI), Ethernet and Firewire