The control unit (CU) is a component of a computer's central processing unit (CPU) that directs the operation of the processor. Central processing unit (CPU): The computer's central processing unit (CPU) is the portion of a computer that retrieves and executes instructions. The CPU is essentially the brain of a CAD system. It consists of an arithmetic and logic unit (ALU), a control unit, and various registers. The CPU is often simply referred to as the processor. The ALU performs arithmetic operations, logic operations, and related operations, according to the program instructions. The control unit controls all CPU operations, including ALU operations, the movement of data within the CPU, and the exchange of data and control signals across external interfaces (system bus). Hence, the correct answer is CPU.