Locating an initial servo track in order to servo write a disk drive from spiral tracks

1. A method of writing product servo sectors to a disk of a disk drive, the disk drive comprising control circuitry and a head disk assembly (HDA) comprising the disk, an actuator arm, a head connected to a distal end of the actuator arm, and a voice coil motor for rotating the actuator arm about a pivot to position the head radially over the disk, the disk comprising a plurality of spiral tracks, wherein each spiral track comprises a high frequency signal interrupted at a predetermined interval by a sync mark, the method comprising:

using the head internal to the disk drive to read the spiral tracks to generate a read signal;

processing the read signal to detect the sync marks in the spiral tracks;

detecting an aberration in the detected sync marks in order to locate an initial radial location of the head with respect to the disk;

processing the read signal representing the high frequency signal in the spiral tracks to generate a position error signal (PES) used to maintain the head along a substantially circular target path; and

using the head internal to the disk drive to write the product servo sectors along the circular target path.

2. The method as recited in claim 1 , wherein at least one of the spiral tracks is missing at least one sync mark at the initial radial location.

3. The method as recited in claim 2 , wherein every other spiral track is missing at least one sync mark at the initial radial location.

4. The method as recited in claim 1 , wherein:

the sync marks comprise a first pattern at the initial radial location; and

the sync marks comprise a second pattern at radial locations different than the initial radial location, wherein the first pattern is different than the second pattern.

5. The method as recited in claim 4 , wherein detecting the sync marks comprises detecting the first pattern at the initial radial location and detecting the second pattern at radial locations different than the initial radial location.

6. A disk drive comprising:

(a) a disk comprising a plurality of spiral tracks, wherein each spiral track comprises a high frequency signal interrupted at a predetermined interval by a sync mark;

(b) an actuator arm;

(c) a head connected to a distal end of the actuator arm;

(d) a voice coil motor for rotating the actuator arm about a pivot to position the head radially over the disk; and

(e) control circuitry operable to write a plurality of product servo sectors to the disk to define a plurality of radially spaced, concentric data tracks by:

using the head internal to the disk drive to read the spiral tracks to generate a read signal;

processing the read signal to detect the sync marks in the spiral tracks;

detecting an aberration in the detected sync marks in order to locate an initial radial location of the head with respect to the disk;

processing the read signal representing the high frequency signal in the spiral tracks to generate a position error signal (PES) used to maintain the head along a substantially circular target path; and

using the head internal to the disk drive to write the product servo sectors along the circular target path.

7. The disk drive as recited in claim 6 , wherein at least one of the spiral tracks is missing at least one sync mark at the initial radial location.

8. The disk drive as recited in claim 7 , wherein every other spiral track is missing at least one sync mark at the initial radial location.

9. The disk drive as recited in claim 6 , wherein:

the sync marks comprise a first pattern at the initial radial location; and

the sync marks comprise a second pattern at radial locations different than the initial radial location, wherein the first pattern is different than the second pattern.

10. The disk drive as recited in claim 9 , wherein detecting the sync marks comprises detecting the first pattern at the initial radial location and detecting the second pattern at radial locations different than the initial radial location.