Areal-Density Capability Measurement Based on 747 Test in Magnetic Recording Systems
A method is presented for determining the areal density (AD) capability of a magnetic recording system based on a set of 747 tests taken over a range of linear densities. By fitting the measured results with a suitable functional form, we can readily predict off-track capability (OTC) at any combination of linear density and track density. Conversely, for a given OTC requirement, we can immediately find the maximum AD that can be reached and the bit aspect ratio required to achieve it. Our results also reveal the effect of skew angle on AD and match well with previous results for perpendicular magnetic recording.
An Off-Track Capability Model Including Noise
An analytical model for off-track capability (OTC) is developed. The model is built on the assumption that, for a given channel, the overall signal to noise ratio (SNR) determines the bit-error-rate (BER). Written magnetization consists of a data track, adjacent tracks and attendant erase bands, and previously written "old information." SNR is determined by the position of the read-back sensor over the medium, and by the characteristic signal, electronic noise, and media noise powers. These parameters are presumed constant for a particular head, disc, and linear density. OTC is determined as the off-track distance beyond which the SNR falls below a given threshold value, which can be correlated to a threshold BER. We compare OTC as predicted by the model to experimental measures of OTC as the track pitch is varied.
Equalization and detection in storage channels
In this work, a model for digital magnetic recording on thin-film media is developed, and the performances of several detector/run-length-limited code combinations are compared under different densities, media noise, offtrack interference, and channel mismatch conditions. The study is based on computer simulations using an experimentally extracted transition response of a magnetoresistive read head. The detection algorithms considered include the partial response maximum likelihood detectors, decision feedback equalizer (DFE), and fixed-delay tree search with decision feedback (FDTS/DF) detector. It was found that the DFE with a (0,k) run-length-limited (RLL) code and the FDTS/DF with a (1,7) RLL code show the least bit error rate degradation, as the user density increases beyond 2.5 bits/PW50. The PRML and DFE suffer less from offtrack interference. The (0,k) coded DFE and the (1,7) coded EPRML and FDTS/DF channels are relatively robust under PW50 mismatch. At a user density of 2.5, FDTS/DF (1,7) and DFE (0,k) are found to yield the best bit error performance under varying intensities of white Gaussian noise and media noise.