Control unit is a CPU’s component which handles all processors control signals. Basically it control the flow of information in the processor and coordinate the activities of different unit of the computer within the processor. Control unit control what happens inside the processor as with the brain of the computer. Control unit tells the Computer’s memory, Arithmetic and logic unit, I/O devices how to respond to program’s instructions. It is a rules of operations or we can say a microprogram which take input an instruction and encode it into a programmable logic array(PLA) and read only memory(ROM). It is considered to be a most complex part of CPU as it determine the clock cycle of the CPU.
The main function it perform is send and receive control signals from the other computer devices and handle related task such as fetching, decoding, execution of the instruction and store result. It also controls sequential instruction execution by guiding data flow oath from different computers. Interprets instruction and regulate and controls processor timing.
This Type of control unit is difficult to design as its high in cost. But the CAD tool used for the computer design which is highly automated, therefore all processors use hardwired only. It is a control mechanism that generate control signals by using finite state machine(FSM).
In 1953 Maurice Wilkes invented microprogram by realised an idea that made control unit easier to design and more flexible. Idea of the inventor determine that a control unit can be implemented as a memory which contain control bits and control flow which sequencing the patterns. In other words we can say it is like a miniature computer which can be programmed to sequence patters of the control unit. As the name implies microprogram it is used to distinguish from ordinary computer program. In microprogram a control unit can be implemented of a complex instruction which is impossible to do in hardwired control. This generate control mechanism by using a memory which is known as control storage(CS).