A disk drive is disclosed comprising a disk having a plurality of servo
sectors defining a plurality of servo tracks that form a plurality of
servo zones. The disk drive further comprises a head actuated radially
over the disk for generating a read signal, and control circuitry
including a timing circuit. The timing circuit is initialized with a
nominal center frequency that approximates an average servo data rate out
of the plurality of servo zones. The timing circuit is synchronized to
the read signal to generate synchronous read signal samples. A servo sync
mark is detected from the synchronous read signal samples, and the servo
zone the head is reading is estimated after detecting the servo sync
mark.