Bus System in Computer

Hello friends, in this article you will get to know about Bus System in computer architecture including Control Bus, Address Bus and Data Bus that is in our computer system. It is one of the most important topics in our computer architecture.


In computer architecture, a bus is a collection of wires, chips, and slots inside the computer through which data are transmitted from one part of the computer to another to and from (in and out) from peripheral devices. It is often compared to a highway (pathways in the computer on which data travels). It is a set of parallel distinct wires, serving different purposes, which allow devices attached to it to communicate with the CPU.
The function of the bus are:
  • It carries information from one component to another.
  • It carries data, addresses, or control signals.
  • One component of the component can interact with others by bus.
The bus consists of three main parts:
  • Control bus
  • Address bus
  • Data bus

Control Bus

The control bus carries the control signal. The control signal is used for controlling and coordinating the various activities across the computer. It is generated from the control unit within the CPU. Different architectures result in a differing number of lines of wires within the control bus, as each line is used to perform a specific task. For instance, different specific lines are used for each of the read, write, and reset requests. These are not a group of lines like address bus and data bus, but individual lines that provide a pulse to indicate a microprocessor operation. The control unit generates a specific control signal for every operation, such as memory read or input/ output operation. This signal is also used to identify a device type, with which the microprocessor intends to communicate.

Address Bus

The address bus carries a memory address within the device. It allows the CPU to reference memory locations within the device. It connects the CPU and other peripherals and carries only memory addresses. In a computer system, each peripheral or memory location is identified by a numerical value, called an address and the address bus is used to carry this numerical value as well as it also contains a few control lines to carry control commands. The address bus is unidirectional, bits flow in one direction, from the processor to a peripheral or a memory location. The address bus contains the connections between the processor and memory that carry the signals relating to the addresses which the CPU is processing at the time, such as the locations that the CPU is reading from or writing to. The processor uses the address bus to perform, identifying a peripheral or a memory location.
If the address bus could carry 8 bits at a time, the CPU could address only (i.e. 2^8) 256 bytes of RAM. Most of the early PCs had 20-bit address buses, so CPU could address 2^20 bytes (1 MB) of data. Today with 32-bit address busses CPU can address 4 GB (over billion bytes) of RAM. Wider the bus path, more information can be processed at a time, and hence it also affects the processing speed of a computer.

Data Bus

Data bus transfers data from one location to another across the computer. The meaningful data which is to be sent or retrieved from a device is placed on these lines. The CPU uses a data bus to transfer data. It may be a 16-bit or 32-bit data bus. It is an electrical path that connects the CPU, memory, and other hardware devices on the motherboard. These lines are bidirectional, data flow in both directions between the processor and memory and peripheral devices.
The number of wires in the bus affects the speed at which data can travel between hardware components just as the number of lanes on a highway affects the time it takes people to reach their destination. Each wire can transfer 1 bit of data at a time, an 8 wire bus can move 8-bit at a time, which is 1-byte data at a time. A 16-bit bus can transfer 2 bytes. 32-bit can transfer 4 bytes etc. Intel 80286 microprocessor used 16 bits of the data bus. Intel 80386 used a 32-bit data bus. As the data bus width grows larger, more data can be transferred.
Bus System: Data Bus, Address Bus and Control Bus - ComputeNepal
Bus Architecture
The transmission of the data on bus lines takes place between approximately 1M baud for the microcomputer to about 1000 M baud or more for the large more expensive computers. (1 baud = 1 bit/sec. )
Communication between the different units of the processing system is carried out along the address and data bus and also along various control lines. All control operations are governed by the master timing source and clock (Quartz crystal oscillator).

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