Patent ID: 7869158

Claim:
A method comprising: receiving a waveform produced by a head operated with respect to a rotating magnetic recording medium, the magnetic recording medium comprising multiple helicoid patterns arranged in a first helicoid group and a second helicoid group; generating first information from one or more portions of the waveform corresponding to the helicoid patterns of the first helicoid group; providing output based on the first information to align the head with respect to a target track of the rotating magnetic recording medium; generating second information from one or more portions of the waveform corresponding to the helicoid patterns of the second helicoid group; analyzing the second information with respect to the first information to generate calibration information, the calibration information compensating for operational differences between using the helicoid patterns of the first helicoid group and the helicoid patterns of the second helicoid group to align the head; providing output based on the second information and the calibration information to maintain the alignment of the head; first switching, from using the first information to track follow on a first target track, to using the second information to track follow on a second target track to write data to the second target track, wherein the first switching comprises using the calibration information; and second switching, from using the second information to track follow on the second target track, to using the first information to track follow on a third target track to write data to the third target track, wherein analyzing the second information with respect to the first information comprises detecting multiple phase differences that are based on the helicoid patterns of the second helicoid group while compensating for phase differences based on the helicoid patterns of the first helicoid group, each detected phase difference being responsive to a difference between a timestamp derived from at least a portion of the waveform that corresponds to a helicoid pattern of the second helicoid group and an expected timestamp.