In order to achieve narrow track pitch by measuring, storing and compensating
common average values for repeatable runout components between adjacent tracks
in a head positioning control system for a magnetic disk drive, a compensation
signal is calculated for the average value of the repeatable runout of each servo
sector of at least two tracks of servo information reproduced from a magnetic disk,
on the basis of an inverse function of the sensitivity characteristics of the tracking
control system. The compensation signal is stored, and thereafter used for compensating
the servo signal.
