Patent ID: 8817403

Claim:
A magnetic disk drive, comprising: a disk comprising a plurality of zones each including a plurality of tracks, the disk being formatted such that a plurality of servo frames are discretely recorded in each of the plurality of tracks, each of the servo frames comprising servo preamble data of a servo preamble length that corresponds to the zone that includes the track, the servo preamble length being less than or equal to a reference length that is common to the plurality of zones; and a controller configured to cause a head to read the servo frames from the disk via a read amplifier, wherein the controller comprises: a read/write channel configured to read a plurality of first servo frames from a track in each of the plurality of zones under a condition that is sequentially changed and set for phase acquisition based on a read signal for servo preamble data, the first servo frames each comprising servo preamble data of the reference length, and a disk controller configured: to determine a respective acquisition condition compatible with each of the plurality of zones based on a result of reading of the plurality of first servo frames from the track in the zone; and to format the disk such that respective pluralities of second servo frames for tracks in the plurality of zones are recorded on the disk, the plurality of second servo frames for a given track comprising servo preamble data adjusted to the servo preamble length corresponding to the determined acquisition condition that is compatible with the zone that includes the given track.