The execution of an Instruction on the computer system involves the control unit of the CPU “fetching,” or obtaining, the instruction from main computer storage and placing the instruction in an instruction register. An instruction register is nothing more than a storage area within the control unit of the CPU which can store a single Instruction at a time.
The control unit will also fetch any data required for the execution of the Instruction and place the data in special “registers” which can be referenced by the arithmetic/logic unit of the CPU.
The arithmetic/logic unit of the CPU is then given control. It will per. form the actual execution of the instruction and store the answer in another register.
The control unit will then place the answer into main computer storage.