The performance improvement of the partial response maximum-likelihood (PRML) system for (1, 7) run-length limited (RLL) code is studied. As a new PRML system, PR (1, 1, 0, 1, 1) system called modified E2PR4 (ME2PR4 ) followed by Viterbi detector for (1, 7) RLL code is proposed. At first, a determination method of the tap weights in transversal filter to equalize to PR (1, 1, 0, 1, 1) characteristic taking account of a noise correlation is described. And the equalization characteristics of the transversal filter are evaluated. Then, a Viterbi detector for ME2PR4 utilizing the constraint of run-length of (1, 7) RLL code is presented. Finally, the bit-error rate is obtained by computer simulation and the performance is compared with that of the conventional PRML systems called PR4, EPR4 and E2PR4 systems with Viterbi detector. The results show that among these systems our system exhibits the best performance and the SNR improvement increases with the increase in the linear density.

Measuring the cross-track profiles of a microtrack created by DC erasing both sides of a recorded track, the linear recording density dependence of the written track fringe width and that of the read track fringe width were successfully separated, both of which are usually observed in combination. It was clarified that when a thin-film head is used for reading, the read track fringe width increases as the linear recording density decreases, whereas it remains almost constant when an MR head with wide shielding layers is used. It was also clarified that the record head fringe width for a thin-film inductive head is less dependent on the linear recording density. The effects of several heads with different pole shapes on track edge phenomena were also evaluated, by partially DC erasing a written track from the track edge and measuring the change in the residual track output. It was found that the fringe field width of a record head changes depending on the pole shape, and the trimming of record head poles is very effective in reducing head field fringe effects.