Introduction of system bus

The bus is a medium or path used to transfer data, memory address and control signal from one part to other part of computers. A bus consists of multiple communication lines. Each line is capable of transmitting signals representing binary digit o and 1.

                             

System bus

A bus that connects all major components (processor, memory and I/O devices) of computer system is called a system bus.

v  A system bus consists, typically, of from about 50 to 100 of separate lines.

v  Each line is assigned a particular meaning or function.

v  Each bus has a clock speed measured in MHz.

v  The size of bus known as its width is important because it determines how data can be transmitted at one time.

                                                       

Address bus

An address bus is a group of wires or lines that are used to transfer the addresses of memory or I/O devices.

Data bus

A data bus is used to transfer data within microprocessor, memory, I/O devices. Therefore, a data bus is used to carry actual data that is being processed

 The data bus consist of number of separate lines is 8, 16, 32, 64 etc. The word length of processor depends on data bus.

Control bus

A control bus is a system bus used by the CPU to communicate with devices that are contained within the computer. It is used for carrying a set of control signals that controls the flow of data.

v  Control signal may be read or write control signal. The control bus carries signals that report the status of various devices.

v  Control signal transmit both command and timing information signal.

v  The timing signal indicates the validity of data and address information.

v  Command signal specify operations to be performed.

Why?

·        Address bus is Unidirectional because the microprocessor is addressing a specific memory location. No outside devices cannot write into Microprocessor. ·        Data bus is Bidirectional because the Microprocessor can read data from memory or write data to the memory. ·        Normally Control bus is unidirectional. But some time control bus is bidirectional, because the Microprocessor needs to know the status of the bus transactions.