Spindle motor controller regulates the motion of a 3-phase motor. It is programmed by the drive microcontroller. There are three control modes of spindle motor operation: the start mode, acceleration mode and stable rotation mode. Let us review the start mode. At power-up a reset signal is sent to the control microprocessor which performs initialization programming internal registers of spindle motor controller for a start. Drive controller generates phase switching signals; the spindle motor at that rotates at low speed generating self-induced electromotive force. Drive controller detects EMF and notifies the microprocessor which uses that signal for rotation control. In the acceleration mode microprocessor speeds-up phase switching and measures the rotational speed of the spindle motor until the speed reaches its rated value. As soon as the rated rotational speed is reached the controller introduces stable rotational mode. In that mode microprocessor calculates the time required for one revolution of the spindle motor based on the phase signal and adjusts the rotational speed accordingly. After relocation of magnetic heads from the parking zone the drive electronics begins tracking the stability of rotation using servo marks.