As mentioned, steppers have not been used in a HDD since they went over 100MB or so. HDDs use a voice coil to position the heads to achieve faster seek times. The photo provided by the OP is the spindle drive motor. This motor does NOT run all the time, being controlled by a logic signal from the computer so that the drive can be shut down for power saving modes, etc. The spindle drive motor, like that for the head motor in a VCR, uses Hall-effect sensors in a brushless DC motor circuit.
Dean