Patent ID: 8335047

Claim:
A disk drive comprising: a slider including a read sensor and a write head; a servo system; and a rotatably mounted disk accessible by the read sensor and the write head, the disk having a set of concentric, discrete tracks formed from thin film magnetic material separated by areas having no magnetic material, each track in the set including a plurality of servo sectors having at least a first offset servo field portion; a centerline of the first offset servo field portion being offset from a track centerline and wherein a downtrack length of the first offset servo field portion systematically varies according to the track position to provide information about the track position through the read sensor to the servo system, and wherein the first offset servo field portion results in a first shift in the read sensor signal at a front of the first offset servo field portion and a second shift in the read sensor signal at an end of the first offset servo field portion as the disk rotates under the sensor and the servo system uses a time between the first and second shifts as an indication of the track position.