Computer systems are now changing rapidly towards directions such as large capacity, distributed and parallel systems. Those systems need scalable high performance file storage systems on the data transfer rate and the traffic. Moreover, some of parallel / distributed systems require on-board disk systems for compact installation.

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  Magnetic disk subsystems should be designed and utilized in order to maximize their performance. In this article, I discuss cross-call pathing, disk cache, and RAID as major technology of the subsystems.

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  Recently, the storage and distribution systems for multimedia information are expected. The advance of digital technologies such as signal processing, network, storage media and LSI devices accelerates the several kinds of multimedia services. The hierarchical, relational and synchronous coding techniques become indispensable.
  Here, The trends of the R&D and the standardization in these coding techniques are described. The storage and distribution systems and subjects of digital storage media are discussed.

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  This paper presents an overview of progress in magnetic disk drive technology, and discuss the future prospects.
  Recent progress of magnetic materials for thin-film heads and media, greately improve the read/write performance, and meets the future prospects of extrmely-high density recording.
  It touches upon the challenges involved in high-density magnetic recording, including the future needs for the novel magnetic materials, and its related problems.

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  We have studied the flying single-pole head and Co-Cr-Ta/Ni-Fe double-layered media for the use in high magnetic recording.
  The media consisted of electro-plated Ni-Fe under layer and sputtered Co-Cr-Ta recording layer. The head formed a 4-layered 60 turns, just like ”PANCAKE” type, the pole-width is 7μm, and the flying height is 3μ”. We have confirmed that a conbination of such midium and a head is capable of achieving high recording density of 300 Mb/sq-in.

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  To keep up with the progress of digitization in broadcasting stations, digital VTRs have been put into practical use. They have rapidly come to be used as a replacement for conventional analog VTRs. On the other hand, thanks to the progress of high density recording technology and image-data compression technology, consumer use VTRs have just begun to indicate the posibility of digitization even for Hi-Vision VTRs.
  This paper reports the present condition of the video recording technology and its prospects, focusing digital VTRs, which have shown remarkable progress in recent years.

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  This paper describes technology for a Co-Ni-O evaporated tape fabricated by a vacuum evaporation method which is called a metal evaporated tape (ME tape), focusing on magnetic properties, microstructure, recording characteristics and noise properties. High reproduced signal output, low noise and high resolution of the ME tape obtained by a ring head are attributed to oblique anisotropy and a particle-like structure. Breakthrough for good durability of the ME tape has been achieved by technology on tribology.

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  This paper discusses Ba-ferrite tape capability in future high density recording systems such as a digital video recording, which is expected to use wavelengths of less than 0.5 μm, the corresponding linear recording densities being greater than 100 kFCI. As important characteristics of Ba-ferrite tapes, discussed in this paper are high density recording performance characteristics, magnetic properties angular dependence, small size particles with high coercivity, switching field distribution (SFDr) for remanence curves, and inter-particle interaction in terms of Henkel plot and delta M plot.

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  Application of perpendicular magnetic recording technology is requisite in order to realize a next generation digital VCR whose recording density is about 1 bit/ μm² . Since ring heads are considered to be used for the digital VCR, tapes must be suitable for the ring heads and digital signal. The tape with tilted easy axis is one of the candidates, which has single-peak-like isolated reproduced waveform, has lower spacing loss factor than that of the tape with non-tilted easy axis, and has high reproduced voltage not only in high linear density region but in low density region.

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  A Co-Cr/Ni-Fe double layer tape was fabricated continuously by facing targets sputtering system. The Co-Cr/Ni-Fe double layer tape medium deposited on a 10μmm thick polyimide film. The read-write characteristics of the tape was investigated using single pole head by conventional cassette VTR. The Co-Cr/Ni-Fe double layer tape that the magnetic layer thickness was 0.33μmm, showed high sensitivity recording and reproducing performance.

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  Soft magnetic thin films such as crystalline Fe-Al-Si (Sendust) alloy films or Co-based amorphous alloy films are practically applied for VCR head core material. Recent research and development of soft magnetic thin films are focussing on a new category of films which having high saturation induction over 1T with a corresponding increase in coercive force of magnetic recording media. In this paper, the characteristics of several soft magnetic films such as crystalline, nanocrystalline, multilayer and amorphous alloy films are briefly reviewed. The relation between magnetic anisotropy and permeability is also described for Co-based amorphous alloy and Fe-based crystalline alloy films which are typical magnetic head core materials.

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  The relation between the domain structure of the main-pole film of the single-pole head and its recording characteristics are investigated. The artificial domain control such as the notch-forming along the film sides, the multi-layered film and the very thin film less than 0.1 μm are studied as a main-pole. We conclude that when the spin rotation is dominant in the main-pole film compared with the wall motion, the high sensitivity and resolution are accomplished. Finally, using the thin main-pole film, the D₅₀ of over 150 kFRPI and the error rate of 10^-7 at 170 kFRPI have been demonstrated.

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  This paper gives an overview of magnetization dynamics in thin film heads. The relationship between domain wall motion and magnetization rotation is essential in both impedance noise and Barkhausen noise. A model which describes coupled wall motion with magnetization rotation proposed by the author is compared with other models.

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  The magnetization configurations in magnetoresistive (MR) film with the longitudinal bias are analyzed using the computer simulation based on the Landau -Lifshitz -Gilbert equation. The simulated magnetization configurations explain the assymmetric sensitivity along the track width of the MR film.

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  Sputtering phenomena occurred at surface layer of cathode in glow discharge and deposition mechanisms of arriving particles on substrates are physically explained. For preparation of magnetic thin films in media and heads for perpendicular recording system, ideal requirements of sputtering techniques are listed up and designs of sputtering equipments proposed and developed until now are introduced with their merits. Also subjects and views of sputtering techniques in near future will be described in detail.

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  Physical properties of plasma and its effect on film structure such as phase and morphology is discussed based on results of plasma diagnostic for plasma evaporation and sputtering. Fe-N films, as an example, are systematically synthesize by using above two independent methods referring the results of the plasma diagnostic and magnetic properties of Fe-N films are investigated. New thin film fabrication technique which uses a surface phonon mode of the substrate excited by surface acoustic waves (SAW) is proposed to control the morphology of very thin film.

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  A new sputtering source has been proposed, especially aiming to fabricate a Co-Cr composite medium for perpendicular magnetic recording. The source consists of facing side walls and a bottom plate of a source magnetic material. The wall targets work as a part of a magnetic circuit for getting a strong enough magnetic field. Targets of permalloy and Co-Cr were constructed for a test. A well confined plasma makes discharge characteristics of low discharge voltages very stable even at low argon gas pressures. Wide film thickness homogeneity was obtained due to the collimated atoms sputtered from the gun structure type target. Recovery factor of sputtered materials to the substrate was 10 times or more than those of conventional sources. The deposited permalloy films show low coercivities with high crystal orientations even at a high input power. These imply that the new sputtering source is one of promising means for fabricating Co-Cr composite media with a high throughput.

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  For down-sizing and increasing capacity of disk file memories, a servo technology for micron trackwidth is one of the most important themes to realize high recording density. Three key problems for micron trackwidth servo are investigated. They are a high SNR of position error signal, a gain variation caused by head/pattern width variation, and a dual-stage actuating. It is shown that over 12dB of SNR(electrical) is necessary for tracking around 1μm trackwidth head. And a new dual-stage servo system is proposed for a high performance tracking technology.

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  Conventional helical-scan magnetic recording requires precise head tracking, precise tape path and accurate servo control for them.
  We have developed a magnetic tape recording system based on a new concept, "Non-tracking Method" which requires less accuracy of them. By combining double track scanning and data rearrangement through a memory divice, all data can be reproduced in correct order without precise head tracking. When track pitch is 9.8μm, the non-tracking method expands the tolerance on head tracking to plus and minus 100μm, while the head tracking tolerance of plus and minus 5μm is needed in conventional recording.
  Using the non-tracking method, a newly developed rotary head drum loading system which is called "non-tape-loading" and also a newly developed metal-evaporated tape, we have developed a extremely high density digital audio tape recording system, including a stamp-sized tape cassette and a tiny digital audio recorder. Two hours stereo digital recording is realized with the tiny cassette.

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  To attain a high recording density and increase recording bit-rate on digital VCRs, we studied application of multilevel/ phase modulation for magnetic recording channel. This paper is to report that a recording density substantially higher than the one attained by an NRZ modulation method can be realized by using a Trellis coded 16 quadrature amplitude modulation (TC-16QAM) method and improve TC-16QAM. This is experimentally proved by a high density recording of 0.83 μm²/bit (0.78 Gbit/inch²) established by using an improved TC-16QAM.

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  This paper outlines the basic features and applications of partial-response and maximum likelihood sequence estimation signal processing in digital magnetic storage. The paper also introduces a practical examle of PRML channel combined both these technologies. Especially, PR(1,0,-1) decoding way using Viterbi detector is reviewed in a circuit structure, a timing recovery way and the performance. Moreover, several advanced signal processing technologies applicable to the magnetic storage are examined for future developments.

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