Abstract: In a servo system for a hard disk drive, a malfunction detection circuit monitors a period of a sync signal contained in servo data and outputs a malfunction detection signal indicating that there is a malfunction relating on the servo data. The malfunction detection circuit delivers a malfunction detecting signal when a generation period of a sync signal is longer or shorter than a predetermined cycle initially set. The malfunction detecting circuit includes a pulse generator for generating a pulse signal which is synchronized with the sync signal and first and second pulse generators for measuring a period of the sync signal.

Abstract: According to this invention, in a magnetic disk device for recording/reproducing data using a magnetic head, a position of which is controlled by a sector servo method, a tracking speed of an AGC amplifier is set to be a first speed (about 10 .mu.s) in an AGC address area and an AGC burst area, and the tracking speed of the AGC amplifier is set to be a tracking speed (about 20 ms) lower than the first tracking speed in an intersector gap, a gap, a block address area, and a data area.

Abstract: In an apparatus for controlling a moving speed of a magnetic head, servo data recorded beforehand on a recording medium is read out in sequence by the magnetic head while the magnetic head is moving. Position data indicative of the current position of the magnetic head is acquired on the basis of the read-out servo data and then a moving speed of the magnetic head is computed from the position data. When the remaining distance from the current position to the target track is less than a predetermined number of tracks, the speed of the magnetic head is so controlled that the rate of change in the target speed gradually decreases. The control gain is changed in accordance with the rate of change in the target speed.