Head position calculation method in magnetic disc apparatus

A method of calculating a position of a head in a magnetic disc apparatus which has each of annular tracks as a unit of a recording area on a disc, performs positioning control of the head within a track range on the basis of four burst data A, B, C, and D recorded in advance in the tracks, and records/plays back data in/from the tracks using the head, the method comprising:

• when each of the tracks includes a plurality of annular sub-tracks in combination, each of the sub-tracks always has only two of the burst data A, B, C, and D, and the sub-track having burst data A and D, the sub-track having burst data A and C, the sub-track having burst data B and C, and the sub-track having burst data B and D are repeatedly arranged in an order named, in accordance with equations 1 and 2, determining a value of a constant n within a range of 1.2 (inclusive) to 1.8 (inclusive) so as to obtain linearity between a position in a radial direction of the disc and a position P of the head in the radial direction of the disc in the sub-track, and calculating the position P of the head using the determined constant n and equations 1 and 2:
• P=(A−B)*|A−B|(n−1)/(|A−B|n+|C−D|n) (1)
• P=(C−D)*|C−D|(n−1)/(|A−B|n+|C−D|n) (2)