We propose precise write-time compensation for nonlinear transition shift in magnetic tape recording using d=1 runlength-limited (RLL) code as a channel modulation. In this write-time compensation approach, the write current transitions having a transition within 3 bits earlier are shifted so as to minimize the transition shift of the readback signal. First, we precisely measured the nonlinear transition shift using a VCR. Next, based on this measurement, we simulated the effects of the write-time compensation, verifying them in recording experiments with a VCR. The results show that when the optimum read equalization is applied to the readback signal, this write-time compensation approach increases the eye height and eye width while improving the byte error rate by about two orders.

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.

Simplification of the Viterbi algorithm and the error rate performance are presented for a partial response maximum-likelihood (PRML) system employing the PR(1, 1) system as a PR system for (1, 7) run-length limited (RLL) code. The minimum run-length of 1's or O's in the output sequence of the precoder for (1, 7) RLL code is limited to 2. Two kinds of simplified Viterbi algorithms using this run-length constraint are proposed. One algorithm requires the path memory length of only two in the Viterbi detector. The Viterbi detector based on the other algorithm is equivalent to the simple PR(1, 1) system followed by a threshold detector. The bit-error rates of PRML systems with Viterbi detectors based on these algorithms are obtained by computer simulation and their performance is compared with that of conventional PRML systems for (1, 7) RLL code. It is shown that the proposed PRML system exhibits better performance than conventional PRML systems at high recording density.