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Definition: control unit

(1) See microcontroller, ECU, process control, industrial automation and control network.

(2) Within the CPU, the circuit that locates, analyzes and executes each program instruction residing in memory. See ALU.

(3) Within the computer, the hardware that performs the transfer of data to and from a peripheral device, such as a hard disk or screen. See controller.

A Rather Large Control Unit
This is the CPU control unit of the ILIAC IV computer in the 1960s. Today, the equivalent circuitry fits on the head of a pin. (Image courtesy of The Computer Museum History Center, www.computerhistory.org)