Patent ID: 7920355

Claim:
A disk drive comprising: a head which reads and writes data; a disk which has a substrate, a data region and servo regions, the data region provided on the substrate and having data tracks formed and arranged in a radial direction of the disk, each track being constituted by a projecting magnetic layer, and each servo region provided on the substrate and having a bit pattern of servo data and comprising projecting magnetic layers and concave nonmagnetic layers; and a reproduced-signal processing unit which processes a reproduced signal read by the head from each servo region of the disk, thereby to decode the servo data, wherein in each servo region, dividing grooves of nonmagnetic layers are provided in a projecting region in which projecting magnetic layers lie one after another, each having a length equal to or larger than a prescribed length, as measured in a circumferential direction of the disk, each dividing groove being shorter than the prescribed length and dividing a projecting magnetic layer into parts, and non-servo data parts of magnetic layers are provided in a concave nonmagnetic region in which dividing grooves are continuously arranged for a distance equal to or longer than a prescribed distance in the circumferential direction of the disk, each non-servo data part being shorter than the prescribed distance and suppressing reproduction noise resulting from the dividing grooves, the servo data is recorded in each servo region, as encoded data generated by bi-phase encoding and being a data-bit train consisting of 0s and 1s; and the reproduced-signal processing unit includes a unit which decodes the data-bit train from the encoded data read by the head, in each servo region, the projecting regions correspond to “1111” which is included in a bit-pattern contained in the encoded data recorded as the servo data, and the concave regions correspond to “0000” which is included in the bit-pattern.