Patent ID: 7224548

Claim:
In a disk drive that includes a disk and a head that reads from and writes to the disk, wherein the head writes to the disk in response to a write current, and the disk drive generates a position error signal (PES) to position the head relative to the disk in response to the head reading a servo sector on the disk, a method of determining a contact write current that causes the head to contact the disk, the method comprising: generating PES's in response to the head reading servo sectors on the disk; calculating PES variances, wherein each PES variance is a statistical measure of a different group of the PES's; calculating a change in the PES variances; and selecting the contact write current in response to the change in the PES variances; the method including calculating a first PES variance and then a second PES variance, and selecting the contact write current in response to the second PES variance exceeding the first PES variance by a threshold.