International Business Machines Corporation

Frederick E Axmear

Michael M Siverling

Duane W Baxter

David W Collins

John H Saxman

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.

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Rochester, MN, United States of America

Frederick E Axmear