Patent ID: 7312946

Claim:
A disk drive comprising: a head configured to read data recorded on a disk medium; an actuator configured to move the head in a radial direction on the disk medium; and a servo processor which uses servo information recorded on the disk medium to drive and control the actuator and performs positioning control of the head to a target track position on the disk medium, wherein the servo processor acquires burst values as amplitude values from servo burst patterns included in the servo information on the basis of a reproduced signal output from the head, and includes: a tangent calculating unit configured to calculate a tangent-equivalent value from the burst values; a memory configured to store information representing an inverse function approximate expression structured on the basis of characteristics of the tangent-equivalent value converted on the basis of the burst values and the off-track position of the head; a phase calculating unit which uses an inverse function approximate expression stored in the memory to calculate a phase-equivalent value from the tangent-equivalent value calculated by the tangent calculating unit; and a position calculating unit which uses the phase-equivalent value calculated by the phase calculating unit to calculate the off-track position with respect to the target track position.