Control Unit –

Control Unit –

The control unit controls the entire operations of the computer and the CPU. It controls all the other devices connected the CPU. Input devices, output devices, auxiliary Memory etc. hence, the control acts as the never centre of the computer.
The control unit upon receiving an instruction decides what is to be done with it. That is, whether it is to be sent to the ALU for further processing or to the output devices or to the memory etc. in other words the control unit coordinates and controls all hardware operations.

The control unit has an electronic clock that transmits electronic pulses at equal interval of time. The control unit gives instructions to other devices based upon these pulses. Suppose there are three instructions to be performed. Let the first instructions take three clock pulses to complete; when the fourth clock pulse is received the control unit would start processing the second instruction and so on. Suppose an instruction takes three and for the fourth clock pulse to complete and take up the next instruction with the fifth clock. Pulse.

Registers –

The CPU consists of a set of registers which are used for various operations during the execution of instructions. CPU needs registers for storing instructions as well as for storage and manipulation of temporary results.

1. Fetch: To bring the instructions from main memory into the instruction register.

2. Decode: Decoding means interpretation of the instruction to decide which course of action is to be taken for execution of the instruction and what sequence of control singles must be generated for it.



3. Execute: The instruction is execute after the fetching of operands is complete. The control unit is responsible for sequencing the steps necessary to complete.