What is a system bus? What are its types?

A system bus is a single computer bus that connects the major components of a computer system, combining the functions of a data bus to carry information, an address bus to determine where it should be sent, and a control bus to determine its operation. The technique was developed to reduce costs and improve modularity, and although popular in the 1970s and 1980s, more modern computers use a variety of separate buses adapted to more specific needs.

Different Types Of System Buses

Data Bus:

Data bus is the most common type of bus. It is used to transfer data between different components of computer. The number of lines in data bus affects the speed of data transfer between different components. The data bus consists of 8, 16, 32, or 64 lines. A 64-line data bus can transfer 64 bits of data at one time.

Address Bus

Many components are connected to one another through buses. Each component is assigned a unique ID. This ID is called the address of that component. It a component wants to communicate with another component, it uses address bus to specify the address of that component. The address bus is a unidirectional bus. It can carry information only in one direction. It carries address of memory location from microprocessor to the main memory.

Control Bus

Control bus is used to transmit different commands or control signals from one component to another component. Suppose CPU wants to read data from main memory. It will use control is also used to transmit control signals like ASKS (Acknowledgement signals). A control signal contains the following:

1. Timing information: It specifies the time for which a device can use data and address bus.
2. Command Signal: It specifies the type of operation to be performed.
   Suppose that CPU gives a command to the main memory to write data. The memory sends acknowledgement signal to CPU after writing the data successfully. CPU receives the signal and then moves to perform some other action.

• MEMORY WRITE - Write data to a given location in main memory.
• MEMORY READ - Read data from a given out put device.
• I/O WRITE - Write data to a given output device.
• I/O READ - Read data from a given input device.
• BUS REQUEST - Request for a control on the bus for transmitting data.
• BUS GRANT - Indicate the grant of the bus to a device.

References:

1. System bus - Wikipedia
2. Discuss Different Types of System Buses