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.
The subset of the multiple tracks being boundary tracks of established zones of
a disc. Data representative of the radially-dependent repeatable run-out control
components for the subset of the multiple tracks is then stored in a table. The
stored data representative of the radially-dependent repeatable run-out control
components is utilized to interpolate or extrapolate the radially-dependent repeatable
run-out control components for tracks within a zone or outside of the zones for
which data is known.