The various components of a computer are interconnected by wiring systems ensure the transmission of signals necessary for its operation. As it is hardly possible to connect each unit to every other computer, it uses lines operated jointly by all devices attached to it, called the bus cable assemblies by analogy with transport city of the same name.
A bus can be used by all units are connected, but never by more than two of them at the same time it raises problems of expectation and arbitration requests of use. A special circuit, called a bus controller, is appointed for the purpose of organizing all access and avoids conflicts that could occur within the computer.
A bus is capable of carrying signals corresponding to three fundamental types of information: addresses (which identify the location of a device or a data in memory), data and commands (such as for example the clock signals synchronization).
A bus is finally characterized by the number and arrangement of its lines and its operating frequency in megahertz (MHz): A bus has 16 lines for example is a parallel bus 16 bits, which means that each line is able to carry 1 bit at a time. The operating frequency of this bus is used to calculate bandwidth, ie the flow of information it can convey in the same period. If our 16-bit bus operates at a frequency of 8 MHz (recall: 1 Hz = 1 pulse / s), we can estimate the theoretical bandwidth maximum: 8 x 16 = 128 Mbit / s or 128 / 8 = 16MB / s.