Patent ID: 7855850

Claim:
A disk drive comprising: a detecting unit configured to detect a positional change of a read head from the amplitude of a detection signal having a specific shape reproduced from a multi-spiral servo pattern recorded in a disk; a correcting unit configured to correct a positional error that is required in positioning the read head, based on the positional change detected by the detecting unit; a controller configured to control the positioning of the read head, by using the positional error corrected by the correcting unit; and a positional-error calculating unit configured to select those of frames obtained by dividing the detection signal at regular intervals, which are associated with servo-burst signals in the disk, in accordance with similarity in amplitude change, and to perform a positional-error calculation, using the amplitudes of the frames selected, wherein the correcting unit adds an offset determined from the positional change of the read head, to the result of the result of the positional-error calculation.