What Is The Control Unit Inside The PC?

This is vital component of the central processing unit and controls all the activities of computer system. Its role is to decode and execute instructions one at a time. An instruction is a command executed by the processor. There are two basic types of instructions. One is operation instructions. They perform operation on the operands. These instructions must define both the operand involved either explicitly or implicitly. Explicitly operands are defined by the programmer as operands or operand addresses in the instruction field. The implicit operands are fixed by the processor designer and in this case there s no freedom of choice for the programmer. The second is control instructions. They modify the normal sequence of operation in the program. It can be said that such instructions control the flow through the program.

Normally a program is executed in sequence that is the next instruction is obtained by adding 1 to the contents of the program counter which stores the address of the instructions to be executed. The subsequent instruction is always placed immediately in the instructions register after the one being executed. However control orders can conditionally or unconditionally change this sequence. With this the program can jump back to the previously executed code or can jump over some unexecuted piece of code.

Control Unit: In computers Control Unit can be defined as a circuitry that directs CPU operations it is a part of a CPU (Central Processing Unit), in fact in other devices there are control units that directs the operations. The control unit is just like finite state machine that has finite states and the switching between those states is called the actions.
So one can simply define that the control unit is just like a coordinator in an organization that coordinate the activities from different devices going through the processor and controls processes which are currently active inside processor which in turn controls rest of the computer. Earlier the control units for CPUs where on ad-hoc logic but now in modern age computers, it is designed as a microprogram which is stored in a "control store". And the micro sequencer selects the instructions from that microprogram, which controls different parts of devices which could be Buses, off chip I/O(Input Output) ALU (Arithmetic and Logic Unit) which performs the arithmetic operations such as addition, subtraction etc or logical operations such as AND, Exclusive OR, etc, etc. In today's modern age the each these subsystems may have there own control unit, which is supervised by a central control unit