In sensorless operation of spindle motors in hard disk drives (HDD), open-looped starting is used to spin up the motor from standstill to a speed that is high enough to reliably detect back-electromotive force (back-EMF) generated in the armature windings. Then the back-EMF zero-crossing points (ZCP) will be used to detect speed and position for closed-looped control. This paper studies three open-looped starting modes for spindle motor. Six-step, which is currently used in HDD, twelve-step, and sine wave starting are illustrated and compared. The simulation results show that twelve-step and sine wave starting can obtain much better starting performance for spindle motors.