A control unit or CU is circuitry that directs operations within a computer's processor. It lets the computer's logic unit, memory, and both input and output devices know how to respond to instructions received from a program. Examples of devices that utilize control units include CPUs and GPUs.
A control unit works by receiving input information that it converts into control signals, which are then sent to the central processor. The computer's processor then tells the attached hardware what operations to carry out. The functions that a control unit performs are dependent on the type of CPU, due to the variance of architecture between different manufacturers. The following diagram illustrates how instructions from a program are processed.