Patent ID: 7068461

Claim:
A disk drive comprising: (a) a disk comprising a plurality of tracks, wherein: each track comprises a plurality of data sectors and a plurality of servo sectors; each servo sector comprises a plurality of servo bursts written using perpendicular magnetic recording; each servo burst is written at a servo burst frequency; a fill pattern is written between the servo bursts using perpendicular magnetic recording at a frequency substantially equal to an even harmonic of the servo burst frequency; and a phase shift occurs in a read signal at the transition between the servo burst and the fill pattern; (b) a head actuated over the disk for generating the read signal; (c) a sampling device for sampling the read signal to generate a sequence of read signal sample values; and (d) control circuitry for demodulating the servo bursts from the sequence of read signal sample values by computing a single-point Discrete Fourier Transform (DFT) at the servo burst frequency.