Notes

System Bus-The system bus is a cable which carries data communication between the major components of the computer, including the microprocessor. Not all of the communication that uses the bus involves the CPU, although naturally the examples used in this tutorial will centre on such instances.

The system bus consists of three different groups of wiring, called the data bus, control bus and address bus. These all have seperate responsibilities and characteristics, which can be outlined as follows:

Control Bus
The control bus carries the signals relating to the control and co-ordination of the various activities across the computer, which can be sent from the control unit within the CPU. Different architectures result in differing number of lines of wire within the control bus, as each line is used to perform a specific task. For instance, different, specific lines are used for each of read, write and reset requests.

Data Bus
This is used for the exchange of data between the processor, memory and peripherals, and is bi-directional so that it allows data flow in both directions along the wires. Again, the number of wires used in the data bus (sometimes known as the 'width') can differ. Each wire is used for the transfer of signals corresponding to a single bit of binary data. As such, a greater width allows greater amounts of data to be transferred at the same time.

Address Bus
The address bus contains the connections between the microprocessor and memory that carry the signals relating to the addresses which the CPU is processing at that time, such as the locations that the CPU is reading from or writing to. The width of the address bus corresponds to the maximum addressing capacity of the bus, or the largest address within memory that the bus can work with. The addresses are transferred in binary format, with each line of the address bus carrying a single binary digit. Therefore the maximum address capacity is equal to two to the power of the number of lines present (2^lines).