Disclosed herein is a servo system for performing head positioning control
in a disk drive, thereby to move the head to a desired position on a disk. The
servo system perform a learning operation, thereby calculating a learned value
relating to a disk-runout, and effects servo compensation to suppress a disk-runout,
by using the learned value. Further, the servo system abandons erases the learned
value in a memory when an impact applied to the disk drive and exceeding a tolerance
value is detected during the learning operation.
