Dual reference track scheme

Abstract

A method and apparatus for performing adaptive calibration of a disk drive assembly and for determining an offset value to compensate for differences in servo head to data head distance from a nominal value. The present invention has particular application in a relative track count servo system where absolute track position is not known from a reading of the servo track itself. In the preferred embodiment, a single head assembly having both a data head and a servo head is utilized. The distance between the data head center and the servo head center must be known so that a disk written on one drive assembly can be read in another drive assembly. This distance is a nominal value but may vary due to manufacturing tolerances. In the present invention, both the data and servo heads are utilized to establish a servo anchor reference track and to determine an offset correction value to compensate for variations in the servo/data head spacing. A dual reference track architecture is employed on the disk surface. The data head is positioned over the first reference track and centered to within a desired accuracy. Once the data head is in place, the servo track beneath the servo head is established as the anchor reference servo track. The heads are then moved across the disk until the data head is positioned over the center of the second reference track. During this movement, the servo tracks are counted to determine the number of servo tracks between the first reference track and the second reference track. This count is then compared to a table storing the number of servo tracks crossed when the data/servo head distance corresponds to the nominal value. The difference in the actual number of tracks crossed and the stored value is used to generate an offset value to compensate for data/servo head distance variations during seeks and other positioning operations.