Controlling the unit

The control unit handles the execution of a program which is already decoded into the hardware specific machine language. This is done by interpreting the machine code and then executing the required steps.

The command cycle

The CU has to execute 5 main steps during a instruction cycle; which are:

1. Fetch: Obtain the instruction from memory.
2. Decode: Interpret the instruction's opcode and operands.
3. Load: Retrieve any necessary data from memory or registers.
4. Execute: Perform the operation (e.g., arithmetic or logical operation).
5. Write: Store the result back into memory or a register.

This cycle runs until the program ends (or the CPU receives an interrupt), which is sometimes denoted by a 6th interrupt step.