Concept of System Buses (Computer Architecture)
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 transmit from input device to CPU, CPU to memory are common examples of system bus.
The path through which data and instruction flow is called bus of computer. It is a collection of wires, chips and slots inside the computer through which data and information are transmit from one part of computer to another.
Normally, Bus is available from 1 bit and above. The width of the bus determines how much data can moved at a time. Nowadays, PATA cables are replaced by SATA cables because of faster and small in size. These are also a way of transferring data and information from HDD to memory. Beside these cables there are numbers of buses inside the computer system (motherboard). There are three types of System bus they are :
1) Address Bus
The pathway through which transmit of address of memory location is called address bus. All types of memory devices have microscopic memory cells which are identified with unique humans 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 receive memory location from the CPU. There is one way flow in address bus.
2) Data Bus
The pathway (circuit / chips / wires / slots) through which transmit of data from one memory location to other is called Data Bus. When the CPU fetches data from memory, it first output the memory address on its address bus. Then the data bus. When writing data to memory, the CPU first outputs the address onto the address bus, then output the data onto the data bus. Memory the reads and stores the data to the proper location. The data flows in bidirectional way.
3) Control Bus
The pathway (circuit / chips / wires / slots) through which transmit of control signal to operate and control devices and software 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 unit of the system. These signals indicate where data is to 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.