What Are The Different Functions Performed By The Control Unit?

The control unit performs different functions. For the conceptual understanding of the fetch and execute cycle. Let take an example how the operation of multiplying two numbers say 20 and 30 is carried out how is it directed by the control unit. The control unit is also shown sending commands to every unit here. Suppose one of the numbers say 30 has already been stored in the accumulator. To achieve multiplication by 20 following steps will be taken in sequence.

Priori to each instruction fetch contents of computer are copied into the memory address register. Immediately after each instruction fetch, contents of computers are incremented by one. So that it is ready for reference to when the next fetch take place, if value 20 has been stored at an address 09 of main memory. Under command from the control unit this instruction is fetched from the main memory address and put in IR using memory registers.

All operation of the control unit and also those of arithmetic and logical units are performed at an incredible speed. These operations are usually synchronized with a electronic clock. This clock is based on the atomic vibrations of a crystal and as such emits million of regularly spaced electric pulses every second.