Unlike most other tools for moving things, stepper motors can tell you exactly how far and how fast they have moved, and which way they are pointing. All electric motors have two basic parts-the armature, which turns, and the stator, which doesn't. Magnetism pushes and pulls the armature with the stator. In a conventional motor, when the armature almost gets to where magnetism is moving it, brushes contact new areas and the magnetic polarity is switched. The armature suddenly has a long way to go again-rather like coaxing a horse forward with a carrot on a stick.
Most conventional motors have only one stator coil, but stepper motors usually have four.
Steppers also use a permanent armature magnet instead of armature coils, commutators and brushes. Stepper motors let the armature catch the carrot, and they magnetically lock the armature into each position. Turning on another coil of the stator and turning off the previous coil moves the armature another step and locks it into a new position. The stepper motor controller rapidly distributes precisely timed bursts of electricity to the different coils of the stepper motor and provides the timing to control the speed. And this is where your Atari comes in.