Patent ID: 7675701

Claim:
A magnetic disk system employing a data surface servo system, comprising: a magnetic disk in which a plurality of servo sectors, each of which is written with servo data including an automatic gain control/phase locked loop (AGC/PLL) pattern, servo timing mark (STM) following the AGC/PLL pattern, and address information following the STM, are formatted, a magnetic head that reads the servo data in the servo sectors, an STM detection circuit that recognizes either long STM configured by part of the AGC/PLL pattern and the STM, or the STM, and generates an STM detection signal, and a sector detection window generation circuit that sets a sector detection window that defines a period in which the servo sectors are reproduced in response to the STM detection signal; wherein when the STM detection circuit does not recognize the STM, the sector detection window is kept in an opened state, and the STM detection circuit recognizes the long STM from a servo sector that is read by the magnetic head later than a servo sector from which the STM is not recognized, and generates the STM detection signal.