Patent ID: 8238052

Claim:
A disk drive comprising: a magnetic disk of the bit-patterned media type, comprising a data record area including data recording bits and a measurement area including phase-shift measuring bits, wherein each phase-shift measuring bit is arranged at a predetermined distance from the cyclic reference position of a data recording bit; a reproduction module configured to output a reproduced signal corresponding to the phase-shift measuring bits on the magnetic disk; and a measurement module configured to calculate a quantization value of the reproduced signal, to find the phase shift measuring bits corresponding to the reproduced signal when the reproduced signal is determined to be indefinite, and to determine the phase shift corresponding to the phase-shift measuring bits found, wherein the phase shift is of a write clock signal, wherein the measurement module is configured to calculate an exclusive logical sum of a present quantization value of the reproduced signal and a quantization value at one clock pulse before the present quantization value, and is further configured to determine that the reproduced signal is indefinite when the exclusive logical sum is 0.