To solve the conventional problem in a disk drive unit that frequent interruptions
be produced in a processor each time a head transits on a servo gate.
To cope with the above-mentioned problem, a head drive unit 17 performs
an off-track check using servo information read by the head 2 whenever the
head 2 transits on each servo gate. Thus, an interruption processing required
by the processor 16 is limited to the cases of either an operation completion
interruption which is produced when a read/write operation is completed normally,
or an error interruption which is produced on occurrence of the off-track or read
error. This enables to reduce the number of interruption processing times performed
in the processor 16, which results in reducing the load of the processor
16.
