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A bstract-Partial response maximum-likelihood(PRML) systems using an MR head and a double layer perpendicular medium are studied. The bit-error rate performance of PRML systems characterized by the polynomials with the positive coefficients for the (1,7) code and the negative coefficients for the 8/9 code is evaluated. The PRML system for the (1,7) code has a large minimum Euclidean distance and a small noise spectrum compared with those for the 8/9 code. This results in a significant performance improvement. Among PRML systems discussed in this study, PR(l, 2, 3, 2, l)ML exhibits the best performance and improves the SNR by about 13.8 dB over that of PR4ML for the 8/9 code at a bit-error rate of 10-4 and a normalized linear density of 2.5.

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