Patent ID: 7538964

Claim:
A magnetic disk drive comprising: a magnetic disk medium in which data and positional information are recorded along a predetermined locus; a magnetic head that moves relatively to the magnetic disk medium so as to write or read the data and read the positional information at every first predetermined timing; and a position control circuit that detects the position of the magnetic head on the predetermined locus according to the positional information read by the magnetic head, and transmits a signal, based on which the position of the magnetic head is controlled, so that the magnetic head will be positioned on a locus in or from which data is written or read, wherein: the position control circuit produces a signal, based on which the position of the magnetic head is controlled, according to the positional information read by the magnetic head, and transmits the signal via a multi-rate filter circuit that operates at the second predetermined timing that comes more quickly than the first timing, decreases a sensitivity function relevant to a predetermined object frequency by a first predetermined gain by advancing a phase relevant to a Nyquist frequency determined at the first timing, and suppresses an increase in the sensitivity function, which relates to frequencies lower than the object frequency, to a second predetermined gain.