Patent ID: 7317591

Claim:
A magnetic disk drive comprising: a magnetic disk for recording user data and servo data; a magnetic head for reading/writing user data and reading servo data at a specified access position of said magnetic disk; a controller to generate a position error signal in accordance with a servo data signal read by said magnetic head and output a control signal for a drive device that moves said magnetic head; a peak filter to input the position error signal, wherein a gain is valid for a preselected frequency; a phase filter to determine the phase of said peak filter; a mechanism to position said magnetic head at the access position in accordance with a control signal output from said controller and a signal output from said phase filter; and a phase comparison frequency updater to compare a phase of the position error signal against an output signal phase of said peak filter, change a preset frequency for said peak filter in accordance with the result of comparison, and change a transfer function for determining the output signal phase of said peak filter in accordance with a change in the preset frequency.