The present invention is directed to a method and apparatus for providing
an absolute reference point on a disk surface of a disk drive. A write
head associated with the disk surface is used to write spirals of servo
information thereon, for example, under control of a servo track writer.
The spirals of servo information include standard spirals and special
spirals. In one embodiment, the special spirals are shorter than the
standard spirals and the special spirals are rotationally non-symmetric.
For example, an unequal number of standard spirals are interposed between
one pair of adjacent special spirals relative to the number of standard
spirals interposed between other pairs of adjacent special spirals. The
special spirals may take a variety of other forms to distinguish
themselves from standard spirals.