Disk file with multiplexed servo system

A disk file includes multiple disks surfaces, on which servo information is recorded, with an offset in azimuth from one disk surface to another. Each head 16 comprises a magnetoresistive stripe 112 for reading and an inductive write coil 110. The servo system reads servo information from each disk in turn, multiplexing the signals from each disk together to form a single position error signal (PES). The separation of the servo multiplexer 130, attached to the MR stripes, from the write multiplexer 120, attached to the inductive coils, avoids problems due to contamination of the servo signal by the write signal. A least squares fit is used to generate the pes from the series of servo samples from each disk surface.