| 主权项 |
1. A disk apparatus comprising:
a disk medium having a data area and a servo area, on the disk medium, a signal of three levels can be recorded onto the data area on a track including first and second sub-tracks in a form of combinations of information recorded on the first sub-track and information recorded on the second sub-track adjacent to the first sub-track, the three levels including a first level, a second level, and a third level between the first level and the second level; and a controller that obtains a likelihood ratio of likelihood of the third level to likelihood of the first level and of the second level based on a signal read from the data area by a head, obtains offset amount of the head from a target position along an cross-track direction and a direction of the offset according to the obtained likelihood ratio, and performs first control to cause the head to approach the target position based on the offset amount and the direction. |
