Patent attributes
A disk unit is capable of detecting a track, the track width of which deviates from a normal value, with high accuracy at high speed. A HDD includes a read head, a disk and defective-track detecting part. The disk has servo data including bursts A, B written thereon. The servo data is used to position the read head to a track center. The defective-track detecting part detects a defective track as below. The sum of the amplitude of bursts A and B, which have been read by the read head by one read operation, is divided by the amplitude of a burst C or D to obtain a compared value. If the compared value deviates from a criterion by a specified percentage or more, it is judged that the track width of a track is abnormal. Since bursts A through D are written without trimming, the size of bursts A through D in the track width direction are kept constant regardless of the track width. Accordingly, a gap G fluctuating in accordance with the track width is formed in the radial direction between bursts A and B. Bursts A and B are read at a position including gap G, and the above-mentioned compared value is determined, and thereby a defective track is detected.
