Method and system for compensation of nonlinearity or fluctuation of head-position signal

A magnetic recording disk apparatus, comprising:

• a magnetic recording disk medium having a plurality of tracks formed thereon in a concentric circle pattern and a servo area formed on a part of each of a plurality of said tracks and used to record a servo pattern;
• a magnetic head provided with a read element and a write element;
• wherein a plurality of patterns are disposed in an area different from said servo area on said magnetic recording disk medium so as to be deviated respectively at least more narrowly than the width of said read element of said magnetic disk head;
• a servo decoder for generating a head position signal from a servo pattern formed on said magnetic recording disk medium;
• and
• means for calculating a convolution integral between a microtrack profile and a step function;
• wherein said microtrack profile is calculated by combining a head position signal from said plurality of patterns;
• a length in the track width direction of each of said plurality of patterns is narrower than the length in the track width direction of said read element, and
• said plurality of patterns have equal lengths in the track direction.