US Patent 7119981 Method and apparatus for tracking radially-dependent repeatable run-out

An apparatus and method for tracking radially-dependent repeatable run-out in a disc drive having a servo loop for positioning a head over a rotating disc is provided. The disc includes multiple tracks. Radially-dependent repeatable run-out control components for at least a subset of the multiple tracks are first determined. Data representative of the radially-dependent repeatable run-out control components for the subset of the multiple tracks is then stored. The stored data representative of the radially-dependent repeatable run-out control components is retrieved before settling on the target track, and subsequently used to follow the selected track.