Patent ID: 7589924

Claim:
A characteristic evaluation method for a magnetic disk, comprising the steps of: (a) rotating the magnetic disk; (b) generating a write clock signal which is linked to the rotation of the magnetic disk; (c) recording a first periodic signal into the magnetic disk in synchronism with the write clock signal, the first periodic signal containing dibits and isolated bits; (d) generating a sampling clock signal which is linked to the rotation of the magnetic disk; (e) reading the first periodic signal from the magnetic disk to provide a first read signal; (f) sampling the first read signal in accordance with the sampling clock signal to provide first sampled data; (g) frequency-analyzing the first sampled data; (h) selecting, from the frequency-analyzed first sampled data, a predetermined odd-numbered order harmonic component with respect to a fundamental frequency; (i) recording a second signal into the magnetic disk in synchronism with the write clock signal, the second periodic signal containing only isolated bits; (j) reading the second periodic signal from the magnetic disk to provide a second read signal; (k) sampling the second read signal in accordance with the sampling clock signal to provide second sampled data; (l) frequency-analyzing the second sampled data; (m) selecting, from the frequency-analyzed second sampled data, the predetermined odd-numbered order harmonic component with respect to the fundamental frequency; and (n) calculating at least one of a partial erasure and a nonlinear transition shift of the magnetic disk from the predetermined odd-numbered order components selected in steps (h) and (m) from the frequency-analyzed first and second sampled data.