An apparatus that controls a head that reads data from and writes data to a recording medium of which a spinning speed is controlled based on a clock signal includes a clock-error detecting unit that detects an error in the clock signal, and a head-retraction control unit that controls the head in such a way that the head is safely retracted when the error is detected by the clock-error detecting unit.

 
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> Magnetic disk drive with servo bursts and alternating magnetic polarity regions therebetween

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