A control unit (CU) is an integrated circuit in a processor that controls the input and output. It receives instructions from a program, then passes them to the arithmetic logic unit (ALU). The ALU performs the appropriate calculations and sends the resulting values back to the control unit. The control unit sends these values to the corresponding program as output.
A typical control unit is comprised of several logic gates and includes two important components:
- Program Counter (PC)
- Instruction Register (IR)
The program counter loads individual instructions from memory and stores them sequentially. The instruction register decodes these instructions and converts them to commands for the CPU. After each instruction, the CU increments the program counter and fetches the next instruction.
Control units operate at the clock speed of the corresponding CPU. Therefore, the control unit of a 3 GHz processor can handle three billion operations per second.