System bus (data, address and control bus)


  • This network of wires or electronic pathways is called the 'Bus'.
  • A system bus is a single computer bus that connects the major components of a computer system.
  • It combines 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.

System Bus
Address Bus
  • It is a group of wires or lines that are used to transfer the addresses of Memory or I/O devices.
  • It is unidirectional.
  • 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).
Data Bus
  • It is used to transfer data within Microprocessor and Memory/Input or Output devices.
  • It is bidirectional as Microprocessor requires to send or receive data.
  • 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.
Control Bus
  • Microprocessor uses control bus to process data, i.e. what to do with the selected memory location.
  • Some control signals are Read, Write and Opcode fetch etc.
  • Various operations are performed by microprocessor with the help of control bus.
  • This is a dedicated bus, because all timing signals are generated according to control signal.

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