Patent ID: 8300337

Claim:
A method for measuring a change of a clearance between a head and a disk, said method comprising; reading a preliminarily written data string for clearance measurement on a disk to obtain a first measured value of Kgrad corresponding to a clearance, said clearance determined by a first linear dependence on said first measured value of Kgrad; writing a new data string for deterioration check onto said disk and reading said data string for deterioration check to obtain a second measured value of Kgrad corresponding to a second clearance, said second clearance determined by a second linear dependence on said second measured value of Kgrad; determining a deterioration of said data string for clearance measurement from a difference between said first measured value of Kgrad and said second measured value of Kgrad; measuring a clearance change using said data string for clearance measurement by a normal operation if said determination is that said data string for clearance measurement has not deteriorated; measuring a clearance change by an operation different from said normal operation if said determination is that said data string for clearance measurement has deteriorated; and wherein Kgrad comprises a corrected tap value of an adaptive cosine filter implemented in a read/write channel of a hard-disk drive; and wherein said first linear dependence and said second linear dependence are characterized by coefficients having different values, said values of said coefficients stored in a non-volatile memory of said hard-disk drive.