Patent ID: 7969675

Claim:
A method of determining a quality of an erase process for a perpendicular magnetic recording (PMR) disk before assembly into a hard disk drive, the method comprising: performing the erase process on the PMR disk; writing a first test pattern of magnetization pulses comprising a square wave portion of magnetization pulses and a portion without magnetization pulses on at least one region of the PMR disk; reading the at least one region of the PMR disk previously written with the first test pattern to identify a second test pattern of magnetization pulses; analyzing the second test pattern of magnetization pulses in relation to the first test pattern by measuring a baseline amplitude based on the portion without magnetization pulses, calculating a maximum difference and a minimum difference between amplitudes of the square wave portion of magnetization pulses, calculating a shift ratio based on the maximum difference and the minimum difference between the amplitudes of the square wave portion of magnetization pulses and the baseline amplitude; and determining the quality of the erase process based on the shift ratio being between 1 and 30.