Definition
Control Unit
The control unit is the part of a processor that generates the control signals for the rest of the datapath.
It decides which operation should happen in the current step, for example:
- which inputs the ALU should use;
- whether memory should be read or written;
- whether a register should be written;
- how the next instruction step is chosen.
In a single-cycle processor, the control unit is mainly determined directly from the instruction bits. In a multi-cycle processor, it is often described by a hardware state machine.
Role
Purpose
The control unit coordinates the execution of instructions.
It does not itself perform arithmetic or store the main processor state. Instead, it tells other components when and how to act.