Abstract: A disc drive having a servo loop for positioning a head over a disc includes a servo controller which generates a servo control signal in response to a received position error signal. An actuator, coupled to the servo controller, moves the head in response to the servo control signal. A sensor, located in the head, senses servo information located on the disc and produces a servo signal therefrom. The servo signal is combined with a reference signal to produce the position error signal. A compensation storage device stores decimated compensation values and a servo compensator expands the decimated compensated values and injects the expanded compensation values into the servo loop.

Abstract: A method for determining servo loop gain of a servo loop in a disc drive includes performing a plurality of seek operations, each seek operation moving a head in a disc drive across a plurality of tracks on the disc. Afterwards, the head is settled over a radial position on a track and a signal is injected into the servo loop at the first frequency. At least two values generated by portions of the servo loop are measured to determine a servo loop gain.

Abstract: An actuator system for positioning a transducing head on an actuator arm over a selected track of a rotatable disc having a plurality of concentric tracks is disclosed. The actuator arm includes a motor responsive to an actuator signal and a bias signal to move the head with respect to the tracks. The actuator signal is applied to the motor to move the head between tracks on the disc. After the head has been moved between tracks, the bias signal is applied to the motor to center the head over the selected track. A lookup table is provided to store predicted bias values in locations addressable by seek direction, previous seek direction, seek length and head position. The bias signal is applied in response to a selectively accessed predicted bias value.