Patent ID: 7630161

Claim:
An apparatus for writing servo data on a disk medium in a disk drive, comprising: a head moving unit which allows a head included in a disk drive to perform a radial seek operation on a disk medium; a first generator which generates a servo clock determining timing for the seek operation of the head; a second generator which generates a sector index pulse to determine intervals at which a multi-spiral servo pattern is written to the disk medium, in which a phase difference between the sector index pulse and the servo clock varies by an amount corresponding to one or more servo clock periods, when one sector of the multi-spiral servo pattern is written to the disk medium; a write unit which allows the head to write the multi-spiral servo pattern to the disk medium on the basis of the servo clock and the sector index pulse; a measuring unit which measures the phase difference between the servo clock and the sector index pulse; and an adjusting unit which calculates the amount of variation of the phase difference based on a measured value from the measuring unit, and adjusts the phase difference to cause the phase difference to be constant, wherein the first generator includes a servo controller which controls the head moving unit and which outputs a position error signal for the head in synchronism with the servo clock, and the measuring unit measures the phase difference between the sector index pulse and the position error signal.