Initial start-up of a polyphase, brushless DC motor (used for a hard disk drive system) is accomplished by sequentially applying current to each of the phases of the motor. When a back EMF zero-crossing is detected in one of the phases of the motor, after an appropriate delay to allow the next phase to come into position, current is applied to that phase. Thus, the position of the rotor is determined from the back EMF zero-crossing of the phase to which power is currently being supplied. A delay proportional to the speed of the motor is used between the detection of a back EMF zero-crossing and the powering of the next phase in sequence. A disk drive motor is brought up to its operating speed of 3600 or 5400 rpm's in successive stages with (1) an initial relatively slow energization of the stator coils (2) zero-crossing detection with a relatively long delay and masking of spurious signals, (3) zero-crossing detection with shorter delay and masking times, and (4) maintaining the rotational speed of disks at the appropriate operating speed using any of various methods commonly known and employed by those of ordinary skill.