In situ FH analysis at disk drive level

Drive-level FH evaluation is important in terms of FH control, FH adjustment and disk drive robustness inside operating hard disk drives. Characterization of FH requires simple methodology, easy implementation in addition to the general requirement to in situ FH analysis. This paper reports authors' effort in proposing a new FH error function to evaluate harmonic ratio FH methods; and based on the error function, a new FH measurement method named multi-frequency method, which calculates FH by reading back multi-frequency pattern, is proposed to minimize FH measurement error by optimizing pattern frequencies. Such technology is also applied at disk drive level to investigate FH variation when a hard disk drive is operating under variable environmental conditions.