What is control Unit?

The Control unit controls the entire operations of the computer and the CPU. It controls all the other devices connected the CPU like input devices, output devices, auxiliary memory etc. Hence the control unit acts as the nerve 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 a

ll hardware operations.

The control unit has an electronic pulse at equal intervals 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 instruction 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 a half clock pulses to complete. In such a case the control unit could wait for the fourth clock pulse to complete and take up the next instruction with the fifth clock pulse. 

The clock pulse basically provides synchronization between the different parts of the computer. The control unit generates millions of clock pulses per second. The speed at which an instruction is executed depends upon the clock speed which is in MHz.