Nonlinearity of perpendicular magnetic recording using a single-pole writing head and an MR head associated with a double layered medium was investigated by the dipulse echo extraction method up to 300 kFRPI and a simulation The nonlinear transition shift (NLTS) was 6% of bit length even in 300 kFRPI The NLTS in length was gradually decreases according to the density increment The NLTS was measured for the condition of less than-40 dB overwrite, thus, no influence of head saturation was confirmed This result was well agree with the proven high recording resolution of perpendicular magnetic recording By investigation based on the simulation, the shape of the extracted echo for the perpendicular head/medium showed that it consisted not only of NLTS by one bit prior, but also of slight width change of the proceeding pulse by a preceding transition Through this study, perpendicular magnetic recording with an head showed good linearity which was suitable for recent signal processing for high density recording

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A DC component suppressing method, called Guided Scrambling (GS), has been proposed. GS constructs a selection set of channel bit streams by subjecting a source bit stream within a data block to several kinds of scrambling and to RLL (Run Length Limited) coding. The one which has the least DC component is then selected. Typically, this technique uses a convolutional operation or GF (Galois field) multiplication. The convolutional GS is good at suppressing the DC component, but has poor performance in the symbol error rate because a bit error propagates to an adjacent codeword before RS decoding. In the GF multiplicative GS, the error rate is lower, but performance in DC component suppression is worse, especially when a simple hardware configuration is used or when a source bit stream is not random. In this paper, we propose the GF additive GS method which generates a better channel bit stream with both these characteristics. We also analyze the spectrum and the average symbol error rate of this method with computer simulations, and show its advantages over other GSs.

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We propose new channel coding for high-density recording, which is intended for use in high-capacity tape storage and optical disk systems. The new 8-16 channel coding improves recording density, facilitates clock recovery, and improves equalization quality. The codes and coding techniques enable effective control of the running digital sum (RDS) for suppression of low-frequency content, while strictly adhering to the (d, k) constraint. The new 8-16 channel coding is the first code which achieves (d, k) = (3, 10) (in NRZ notation) among the rate 1/2 codes which suppress low-frequency content. Computer simulations have demonstrated that the channel coding suppresses the low-frequency content of the encoded sequences equivalently to a DC-free Eight-to-Fourteen Modulation (EFM), producing a 6% higher information density.

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A searching method using genetic algorithms is studied for the optimal tap configuration of nonuniformly spaced transversal filter in digital magnetic recording. A model of the recording/reproducing channel and the genetic algorithms are described. The bit-error rate (BER) performance of nonuniformly spaced transversal filter equalization for a PR4ML channel with partial erasure is obtained by computer simulation and is compared with that of conventional uniformly spaced transversal filter equalization. At a BER of 10^-4, the nonuniformly spaced transversal filter equalization yields a gain of 1.0dB over the conventional uniformly spaced transversal filter equalization.

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A new electrostatic torsion mirror with a silicon/silicon structure has been developed for optical heads. It positions the beam spot accurately on an optical disk having a high track density. This torsion mirror is composed of a hexagonal mirror plate, twin supporting beams, and a pair of driving electrodes. The natural frequency of mirror rotation is defined by the moment of inertia of the mirror plate and the stiffness of the beams. The squeeze effect between the mirror plate and the electrodes generates the damping force. These mechanical parameters are designed to satisfy the specifications for a high-frequency positioning of the beam spot. Experimental frequency responses showed that a test model had a second modal mechanical frequency of over 50 kHz, and the characteristics were in good agreement with the designed values. This torsion mirror will make possible more accurate spot positioning than can be achieved using conventional electromagnetic actuators.

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Hard disks are used as recording media for video signals Although they are designed for computer storage, there are some problems in recording video signals on hard disks. We are developing a video hard-disk system that has efficient recording/playback, while maintaining continuity for video applications. A hard disk evaluation tool for video application is indispensable for developing a video hard-disk system, because a conventional benchmark test cannot evaluate it throughly. In this paper, we describe an evaluation tool for video applications, capable of evaluating hard disk performance precisely and capable of aiding the design of the system.

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This paper describes a development of video hard-disk system which records Hi-Vision video signals. It is necessary to guarantee the continuity of video signals by disk units for the video signals recording. This time, with a background of the rise of requests to non-linear editing machine for the Hi-Vision, we have developed the video hard-disk system for the Hi-Vision video signals. Here, an outline of a developed system and results of the recording and playing back experiments on the Hi-Vision video signals are described.

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[in Japanese]

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