Abstract: In parallel track data storage systems, such as disk files, servo information is recorded using a plurality of constant frequency fields each having a phase shift between tracks. Servo information is thus encoded in the phase of the servo pattern instead of the amplitude of the servo signal lobes. Multiple phase shifts per track are used to make the signal constantly varying with transducer head displacement. Phase is measured modulo 360.degree. such that the phase of a given field will go through 360.degree. every M tracks. By using several fields having different values of M, coarse, medium and fine position resolution can be obtained with the same servo pattern and demodulation scheme. Further, using two fields, one field may be split and positioned at either side of the other field to provide a common center for both fields and eliminate error conditions due to factors such as speed variation.

Abstract: A sector servo seek control samples each sector to obtain sector time, the track identification within a sequence of track types and a position error signal for a track location to track location seek. The device during each sector determines the actual transducer track location and the next sector projected track location with respect to the sequence of track types. The projected track location is corrected using the error signal to find the actual location, but if a sector signal is missing or erroneous, the projected location is used as the actual location, permitting a composite correction to be made when a correct sector signal is obtained. The seek time is minimized by using maximum acceleration followed by maximum deceleration while not exceeding a velocity value that would cause the device to overshoot the target track using full deceleration.