9. Actuator

An actuator is often part of a computer control system.

The actuator is a mechanical device or motor which carries out the action or decision made by the control system. 

For example the lens of this digital camera moves in and out according to how much zoom is wanted.

This movement is controlled by an 'actuator'. In this case it is a tiny electric motor that is controlled by a computer control system within the camera.

So an actuator can be absolutely tiny or it can be truly massive such as the devices that open and shut the Thames flood barrier gates.

But they all do the same thing, namely allow a computer to control movement or action.