System Bus

 Concept Of System Buses

As we need a highway to travel from one place to another place. Similarly the input and output of computer system also need a path to transmit data, information and control from one device to another device. The data and instruction have to electrically flow from one device to another device to fulfill the requirements of the user. The data transmit from input device to CPU, CPU to memory, output device to CPU, CPU to output device etc. are common example of system Bus.

A communication pathway used for data transfer among the components of a computer system is called bus.

It is a collection of wires, chips and slots inside the computer through which data and instruction are transmitted from one part of computer to another part. In general electrical pulses are transmitted from source to destination through the system buses.

 

FUNCTIONS OF BUS

•  It travels information from one place to another.
•  It may carry data, address or instruction.
• One component of computer interacts with other via bus. There are three types of system bus.

a) Data Bus                        b) Address bus              c) Control Bus

a)    DATA BUS

The pathway through which transmit of data from one memory location to other occurs is called Data Bus. Data bus is the path through which data transfer takes place from one device to another. When the CPU fetches data from memory, it first outputs the memory address on its address bus. Then memory transfers the data onto the data bus; the CPU can then outputs the data onto the data bus. When writing data to memory, the CPU first outputs the address bus, and then outputs the data onto the data bus. Memory then reads and stores the data to the proper location. The data flows in bidirectional way.

b)    ADDRESS BUS

The pathway through which transmit of address of memory location occurs is called Address Bus. All types of memory devices have microscopic memory cells which are identities with unique numbers known as memory address or memory locations. When the CPU reads data or instruction from memory or writes data to memory, it must specify the address of the memory location it is going to access. Unlike the other buses, the address bus always receives memory location from the CPU. There is one way flow in address bus.

c)    CONTROL BUS

The pathway through which transmit of control signal to operate and control devices and software takes place is called control bus. It is different from other two buses. The control bus is the collection of individual control signals for timing and controlling function sent by the control unit to other units of the system. These signals indicate whether data is to be read or written, whether the CPU is accessing memory or an input/output device, and whether the I/O device or memory is ready to transfer data.