Computer Architecture

The Control Unit is the conductor of the CPU. It decodes instructions and coordinates the movement of data between the ALU, registers and main memory.

The CU sends out control signals along the control bus that tell every other part of the system what to do at each step of the fetch-decode-execute cycle:

• Tell main memory whether the CPU wants to read or write at the current moment.
• Tell the ALU which arithmetic or logic operation to perform.
• Tell each register when to load a new value or pass its current value somewhere else.
• Keep all the components in step using a clock signal.

The Control Unit itself does not do any arithmetic. It just orchestrates the other components.