Stepper controllers can be used to drive stepper motors from your computer. You can select the target position of the motor, measured in a number of equal steps. The step size varies from motor to motor. You can also keep track of the motor's current position based on how many steps the controller has told the motor to move. Of course, this will not take into account missed steps due to external forces changing the physical position of the motor shaft- you would need to attach an encoder to confirm the actual motor position in this case.
