A disk drive uses the integration of the instantaneous velocities of the
heads to estimate the distance the heads travel while latched. The disk
drive can then determine if the heads are properly parked based solely on
the distance traveled, thus avoiding the use of costly sensors. In the
event that the heads cannot be properly parked due to some malfunction,
the disk drive may store a special code in a nonvolatile memory. The
special code directs the controller not to spin up or attempt to load the
heads on any disk, preventing the disk from being damaged by the heads.