The control unit segregates the computer into a characteristic model of its own kind. Mostly used in relation to fetch - execute cycles, it examines instructions stored in a particular program, and causes them to be obeyed in the apposite sequence.

This allows computers the ability to be self-operational, in that, having been presented with a set of instructions, known as the program, the computer can execute the instructions with no further need for human intervention, until of course the program requests interactive input. In obeying these instructions, the control unit is in two-way communication with all other devices.