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  This paper reviews some of the advancements in the research and development of magnetic recording media and heads for applications in high-density information storage systems. In particular, advancements in the understanding of the fundamental mechanisms in perpendicular and longitudinal recording processes, media, and heads are discussed. Advancements in the designs and materials of media and heads, calculations of recording performance, and new measurement techniques are reviewed. It is concluded that the development of magnetic recording technology is accelerating and needs rapid advancements in the research of media, heads, and the head-media interface. Interactions between university and industry can assist in advancing magnetic recording research to achieve the ultra-high areal densities and reliability required for future information storage systems.

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  Consistent advances in magnetic recording products and applications over several decades have resulted from increases in recording density and bandwidth using the same basic design of recording components. Now, new components and recording methods are receiving major development emphasis and are candidates to extend performance beyond today's product achievements. The key winning and losing magnetic recording components and techniques are reviewed and the new challenging designs are considered for future applications
  Magnetic heads, media, and recording methods have evolved in different ways to extend recording performance and density for data storage, and for consumer video and audio recording applications. In particular, the development of new components for consumer recording systems may provide lower cost technology for data storage applications. Some examples of successful application of components to different recording systems will be described.

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  Perpendicular magnetic recording has been expected to be an effective measure for increasing the recording density for future recording systems. Many academic institutes and industrial companies have carried out research and development activities on perpendicular recording. Toshiba Corporation has also carried out intensive research and development activities for more than 10 years and exhibited several outputs, including its unique barium ferrite particulate perpendicular recording media. Practical utilization has been started for .the barium ferrite media. Further promotion of perpendicular recording development is necessary for magnetic recording industry to keep growing and to respond to future expansion to handle the volume of information to be stored.

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  This paper focuses on recording and reproducing processes and recording / reproducing characteristics for perpendicular recording. Two head/medium combinations of current interest in perpendicular recording are reviewed. One is a Single-pole head/Double-layered medium combination and other is a Ring head / Single-layer combination. Perpendicular magnetic recording has feasibility of extremely high density recording because of its demagnetization free character. To realize such high density recording, however, making the most effective use of head-to-medium interaction is important. Moreover, this review indicates that for enhancing the recording and reproducing characteristics, it is indispensable to investigate not only the macroscopic magnetic properties but also the microscopic properties of the medium and furthermore the vectorial magnetization reversal mechanism of the medium. The present situation and future perspective of the application of perpendicular magnetic recording to magnetic recording system are also described in this paper.

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  A Co-Cr double layer medium, with a very thin back layer, was investigated to improve recording performances in perpendicular recording when using a ring head. A very thin (only 100 Å) semi-hard back layer with high B_s has been shown to not only dramatically increase the reproduced output, but also to increase recording sensitivity. The preferred reproduced waveform, with a sharp single peak, has been obtained, showing a small peak shift as small as that seen for a single layer Co-Cr medium. We conclude that these improvements are due to reduced demagnetizing effects in the recording process rather than effects in the reproducing process. A design of this composite medium is also discussed.

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  Read/write characteristics of a combination of a ring head and a Co-Cr medium with a very thin soft-magnetic underlayer are experimentally studied in terms of saturation magnetization of the Co-Cr layer and spacing between head and medium. At narrow spacing, optimum saturation magnetization is in the range of 300-400 emu/cc. Reproduced voltage at low recording density in the double-layered media is always larger than that in single-layer media in the range of 20-200 nm-thick protective layer. However, recording density characteristics of double-layered media, particularly at large spacing, are inferior to those of single-layer media because recording density characteristics at large spacing are strongly affected by a slight deterioration in the Co-Cr layer's magnetic properties. Computer simulation shows that reproduced output is remarkably enhanced by using double-layered media, particularly at a recording density below 100 kFCI.

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  It was already revealed by experiments and computer simulations that an ultra-high density signal over 20,000 FRPM (Flux Reversal Per Millimeter) can be recorded and reproduced by a single-pole head on a Co-Cr/Ni-Fe double-layer medium in perpendicular magnetic recording. In order to widely discuss the conditions which achieve such an ultra-high density recording in magnetic recording systems, computer simulations are carried out on each of magnetic recording, longitudinal, quasi-perpendicular and perpendicular. From the results, it has been shown that the combination of a single-pole head and a double-layer medium composed of a perpendicularly anisotropic recording layer and a soft magnetic underlayer is the most suitable for an ultra-high density recording.

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  The nature of the perpendicular recording process at track edges is of interest in the design of very high track density recording systems. Recording experiments carried out on a large-scale model exhibit across-track curvature of the recorded transitions of perpendicular magnetization. Calculations using a simple three-dimensional analytical recording model suggest that the curvature is associated with the across-track variation of the demagnetizing field produced by the recorded magnetization pattern.

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  After the classic paper by Iwasaki and Nakamura¹ in 1977, a number of commercial efforts were begun in the United States, all intended to provide higher performance data recording systems and media. This paper reviews these efforts and discusses the current status of perpendicular magnetic recording ("PMR") in the U.S.

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  A new head/medium interface for perpendicular magnetic recording is proposed. The interface realizes both a small head-to-medium spacing and a high durability. A stretched-disk is utilized in combination with a small-tip ring head in contact. The disk is composed of a sputter-deposited Co-Cr medium and an aluminum disk frame 95 mm in diameter. The small-tip head is suspended by a pair of springs. Using a head of a 0.25 μm gap length and a low load of less than 0.5 gw, a high half output density D50 of more than 100 kFRPI and a high durability of more than 30 million passes have been obtained. Realization of a high capacity disk of greater than 40 MB is plausible when a double-sided disk with a track density of 560 TPI and a maximum recording density of 85 kFRPI is used.

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  Increasing the capacity of rigid disk drives can be done by improving the linear bit density or by narrowing the tracks. Track density is limited by tolerances of the mechanical head-disk assembly in today's rigid disk drives. These limitations can be avoided, if the magnetic head is able to write wide and to read narrow. The writing width of a modified thin-film magnetic head for perpendicular recording is determined by the width of the leading pole, whereas the reading width depends on the width of the trailing pole. Thus modified thin-film heads for perpendicular recording are suitable for obtaining the desired write-wide/read-narrow performance, which is demonstrated by bit error rate measurements.

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  Some problems must be solved before perpendicular recording of rigid disks can be realized commercially. The most important point is to perform high-density recording. The spacing problem must also be solved. This paper describes the recording process analysis and tribology approach for double-layer glass media and narrow-gap-length film heads.

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  The tribological behaviour of unprotected thin metallic layers on flexible substrates was studied in sliding contact with magnetic heads. Microscopic investigations of the wear mechanism give evidence, that micro-ploughing of the metallic layer with plastic deformation of the substrate takes place during the first passes of the magnetic head. Subsequent surface fatigue of the layer system initiates debris, which causes a drastical increase of the coefficient of friction and a sudden decrease of the read out signal. Key parameters for improving the lifetime are the reduction of defects and the evolution of reliable lubricating top coatings.

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  The bit error rate characteristics for a Co-Cr-Ta single layer perpendicular recording flexible disk medium have been quantitatively examined. A simple data recovery circuit, composed of a differentiator, a peak detector and a discriminator, has been developed for error rate evaluation. 1F-2F data pattern was suitable for time margin evaluation rather than {110} pattern. The obtained time margin for the 10^-9 error rate is 38% at 75kBPI/400TPI recording density. The time margin is eqivalent to conventional flexible disk media. Therefore. the perpendicular recording media are concluded to be sufficient for reliable flexible disk.

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  Recording characteristics of partially oxidized Fe-Co media were improved remarkably by the introduction of an Fe-Co under-layer. In this paper, the effects of the coercive force of the Fe-Co under-layer on recording characteristics were investigated using a ring-type head. The stronger the coercive force of the under-layer, the higher the reproduced voltage and recording density D50, and the superior C/N and overwrite characteristics. Waveforms of a medium whose Fe-Co under-layer possessed a high coerclve force were sharper than those of a medium with low coercive force. We consider that the broadening of the waveforms depends mainly on interactions between the head and Fe-Co under-layer.

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  This paper made an investigation to the interaction between the double-layer perpendicular recording media to an arbitrary head. It was showed that generally speaking the interaction is determined not only by the parameters of head-medium system, but also by the history of magnetization. Under certain conditions the existence of the recording medium will equivalently move the underlayer up to the top surface of the medium and thus greatly improves the field distribution and the written magnetization for the single pole heads. It was also discussed qualitatively that the effect of the interaction might be able to become even better during the actual recording process.

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  We use conformal mapping to obtain exact head field and image field of the recording ring head. With these fields, we study carefully the extent of the deviation of the simple-minded linear superposition from nonlinearity in recording simulation in self-consistent calculation. The bit crowding (bit shift and amplitude reduction) in dibit case was discussed in detail.

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  We have developed the finite element method (FEM) simulation software in which a vectorial magnetization model is introduced into calculations of magnetizations in a recording medium. The new software have made physically accurate simulations of magnetic recording and reproducing processes because the head-to-medium magnetic interaction as well as the nonlinearity of a head and a medium is taken into account. In this paper, simulations of three recording systems, perpendicular, longitudinal and quasi-perpendicular magnetic recordings are performed in order to clear the distinction of recording mechanisms among three recording systems. We conclude that perpendicular components of magnetizations are stable at high densities and a sharp perpendicular component of a head field is necessary for the ultrahigh density recording.

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  In longitudinal magnetic recording on thin film media, the width of magnetization transition can be calculated graphically and quantitatively by taking the influence of demagnetizing field into account. This method can be also applied to perpendicular magnetic recording without taking this influence into account. Using the graphical metnod, not only isolated pulses but also bit density characteristics can be estimated quantitatively in good agreement with measured results.

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  In this paper, spacing characteristics in a film head with a dual-layer medium are analyzed by the two-dimensional finite element method. As a result, it became obvious that the spacing loss coefficient is changed by the signal wave length and it has several minimum points. This phenomenon is peculiar to the film head/dual-layer medium system. Results reveal that, when the spacing between the head and the medium is small, the magnetic circuit of the head and the under layer has low reluctance and film head efficiency increases. This change of head efficiency causes a spacing loss, although the intrinsic spacing loss in perpendicular recording is the same as that in longitudinal recording.

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  The lower sidebands are enhanced on a Co-γFe₂O₃ tape when AM signals and Dual-frequency signals are recorded. The order of enhancement magnitude is AM> Dual-frequency > FM on a Co-γFe₂O₃ tape. On the other hand, the lower sidebands are not enhanced on a ME tape. These phenomena are observed with actual examinations and computer simulations including perpendicular mode. Compared with the results of experiments and simulations, it is conclude that the lower sidebands enhancement depends on tape thickness.

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  The purpose of this study is to increase output voltages at high recording density ( specifically at 150kFRPI ) of single layered Co-Cr media by investigating their dependence on film structures and magnetic properties. The output voltages at 13 kFRPI and 150 kFRPI were measured as a function of perpendicular coercivity (Hc_⊥) film thickness(δ) and saturation magnetization(Ms). Among those parameters, we found Ms to be the most crucial factor. To increase output voltages of single layerd Co-Cr media using a ring head, it is effective to make media with the largest Ms value as long as incoherent rotation gets dominant in the film.

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  We studied the effects of the amorphous carbon underlayer on the magnetic and recording performance for the CoCr films. The carbon underlayer is found to be effective to improve the perpendicular anisotropy of the CoCr films, although it increases the dispersion of the c-axis orientation. The examination of the recording performance shows the underlayer drastically increases the reproduced voltages of the 0.1 μ m thick CoCr film to the values equal to those of the 0.2 μ m CoCr films at the high recording density above 120kFRPI.

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  The "Foot Print [FP]" described in this paper is the remanent magnetization by a stand-still recording with a DC energized ring head. For perpendicular medium, a symmetric dipulse is reproduced from the symmetric transition of the FP regardless of whether the magnetization has an in-plane component or not. In a practical data recording when a head moves, the FPs are recorded at the points where short pulse currents are switched off. The pulse currents are generated one by one with the alternatively reversed polarity corresponding to encoded 1's. In this method, because of the pulse symmetry, there needs no signal equalization and the bit shift measured by zero-crossing detection is greatly improved compared with conventional perpendicular recording, without sacrificing output voltage and independent of media parameters.

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  The Co-Ni-O thin film formed by the CVI process has a columnar structure that slants diagonally in relation to the substrate. It is known that, for the reasons described above, the film has no easy-to-magnetize direction within the plane and that there is a directionality in output reproduction. [1], [2] The orientation of the easy-to-magnetize direction of Co-Ni-O thin film has been analyzed.
 
  The head has also been studied with the objective of fully exploiting the potential capability of the recording medium. In addition, a method for reducing magnetic noise, a problem involving the recording medium itself, has been discussed.

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  An optimum design of a thin film single pole head and a CoCr/NiFe double layer medium for a rigid disk is described. The head is 19 or 40 turns thin film pole head. We tried to separate the spacing losses in writing process from the ones in reading process by measurements. The transition width in CoCr medium is calculated by using a finite element method (FEM) with curling model calculation routine. The output level depends on coercive force Hc and independent of saturation magnetization Ms of media. Media noise level is lower in the lower Ms media. The side cross talk is very small in perpendicular recording, the optimum track width of head in a same track pitch is wider in perpendicular recording comparing to the width in longitudinal recording.

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  Application of high-saturation magnetization material for the thin film head is desirable for achieving high density recording. In this paper, the possibility of realizing high density magnetic recording by thin film heads was studied based on read/write measurements, two-dimensional head field calculations and the reciprocity principle. Three thin film heads with different saturation magnetization and sputtered thin film media were used. Saturation magnetization for each head were 1.0 T, 1.3 T and 2.0 T respectively. It was recognized that a head field at the bottom of the media greater than 1.3 times the coercivity was necessary to obtain high recording density. Recording density D50 over 40 kFCI could be ascertained by the head with 2.0 T pole pieces at the head-to-medium spacing of 0.22 μm. Comparison between longitudinal recording and perpendicular recording are also discussed based on recording density D50.

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  Magneto-optical microscopy using digital image processing is applied to observation of magnetization bit patterns in double-layer media. The bit patterns are found to depend on pole shapes and magnetomotive force. A reversal domain is observed on both sides of a track if the leading pole of the head is wider than the trailing one. The reason is that magnetization bits are written not by the longitudinal component but by the vertical component of head field. Moreover, the patterns become obscure with increasing magnetomotive force because of the saturation of media underlayers. Thin film heads with double-layer media can perform adequately in perpendicular recording by designing pole shapes and setting the magnetomotive force.

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  The initiation of sliding wear involves force interaction between the magnetic recording head and the recording media during sliding contact. The initial stage of the wear process has been examined and reported. Sliding wear features have been found on the surface of carbon-coated standard thin film rigid disk media after sliding contact without significant change in the average friction force. The experimental results indicate that the structure and properties of the carbon film could play an important role in limiting the durability and performance of the magnetic thin film rigid disks. In an attempt to understand the characteristic sliding damage on the thin film rigid media, the sliding contact stress in multilayer thin film rigid media has been analyzed using finite element method. The correlations of the sliding wear feature, structure of the carbon film and the stress state on multilayer thin film rigid media indicate that continuity and uniformity of the carbon film strongly affect the triboiogical performance of carbon-coated thin film rigid disk media.

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  Carbon thin films, were prepared by RF diode sputtering of a graphite target in an mixture of nitrogen and argon plasma. A series of carbon thin films was deposited as a function of nitrogen partial pressure and on different substrates. We observed a systematic variation of film properties with increasing nitrogen partial pressure which suggests that nitrogen will stabilize the diamond sp³ bonding in the films. The friction coefficient is also reduced as the nitrogen partial pressure is increased. For films prepared at low nitrogen partial pressure, the friction coefficient is 0.4. At higher nitrogen partial pressure, the friction coefficient reduced to the steady state value of 0.2.

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  The tribological properties of sputtered carbon overcoats are important for the practical use of hard magnetic disks. The effects of sputtering conditions on the structure and properties of carbon overcoats have been studied in this paper. Carbon films deposited under high bias, low argon pressure and substrate temperature are hard, with the i-carbon structure and large friction coefficient. Carbon films formed under the opposite conditions are soft, with the graphite structure and small friction coefficient.

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  Various protective carbon layers deposited on the surface of CoNi magnetic layer on the Cr/NiP pretreated aluminium alloy substrate are studied in view of wear resistance. Microstructure of the carbon layer is controlled by varying sputtering conditions and targets, especially glass-like carbon target. It is formed that the most wear resistive layer has an amorphous structure characterized by a single 1550cm^-1 peak in the Raman spectrum, while the other layers have ordinary graphite spectrum, with two peaks at 1360cm^-1 and 1580cm^-1.

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  Carbon thin films are used as an overlayer in the magnetic recording media. There are several methods for preparing carbon thin films at a low gas pressure. The Facing Targets Sputtering (FTS) system is one of the best methods for preparing even magnetic thin films on a plasma-free substrate at a high deposition rate and low substrate temperature.
  The structure of the carbon thin films, which were prepared by the FTS system, was amorphous from the viewpoint of the X-ray diffraction. In the laser raman spectrum, the peak which showed the existence of sp³ bond in the carbon thin films was clearly observed. This pattern was the same as that of the i-carbon, that is, the diamond-like carbon.
  This diamond-like carbon thin films were very excellent in the sliding, tap and scratch test. When the substrate was coated with carbon thin films prepared by the FTS system, its surface was protected almost perfectly.

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  Periodic spacing fluctuation of the flying head for magnetic disk drives was measured using optical interferometry. It was found that the spacing fluctuation during the rotation period was independent of the disk speed. This shows that periodic spacing fluctuation is not caused by the acceleration of the disk surface. Measured spacing fluctuations were compared with disk parameters, and two kinds of disk parameters-curvature and torsion of the substrate were found to be the causes of the periodic spacing fluctuations.

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  This report describes a technique for detecting head disk media contact in order to evaluate perpendicular magnetic disk media. The detector uses a small piezoelectric transducer(PZT), attached to the flying head slider, called PZT-Contact Detection Sensor(PCS). It is most useful for evaluating microscopic projections and dust particles adhering to the perpendicular magnetic disk medium surface which could result in head crash. Experimental results and analyses of AE signals derived from the PCS were detailed. To improve the SNR of an AE signal from the PCS, a new frequency converter circuit with a mixer and a new type of PZT, called D-PZT, was developed. Additionally the mechanism of AE signal production from the PCS when head comes in contact with or passes over a projection on the media surface was also clarified.

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  Non-contact start/stop is preferable for reliability of head/media interface. If non-contact can be established, lowering a flying height is possible. Negative pressure slider is suitable for non-contact start/stop because of its self-loading characteristic. The slider setted at the optimized pitch angle, is adjusted to the suitable attitude for self-loading and is loaded without contact.

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  The influence of relative humidity on friction characteristics of thin-film disk media is investigated. The thickness of H₂O layer adhering to disk media varies greatly with relative humidity, lubricant thickness and functional end groups, thus directly affecting the static friction coefficient. A disk medium coated 20 Å thick with a functional liquid lubricant shows a static friction coefficient of less than 0.2, even after a standing time of up to 120 hours under 90% RH.

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  In order to achieve the required Contact Start and Stop (CSS) durability in the rigid disk system, we investigated the relationship between CSS durability and lubricant structures in terms of polar group, chain length, and chain symmetry. The stronger polar group which has a strong intensive adhesion on the disk surface, shows the ability to withstand CSS operations. The long saturated hydrocarbon chain group, with both an extensive cohesion and high packing, leads to higher durability. Based on these findings, we designed and synthesized new lubricants which exhibit further improved performance.

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  Pass wear durability for sputtered CoCrTa perpendicular magnetic flexible disks has been studied from the CoCrTa film preparation condition standpoint. Pass wear durability strongly depends on a sputtering pressure P_Ar. In the low P_Ar region, high pass wear durability, more than 30 million passes, is obtained. However, in the high P_Ar > 7 mTorr, the durability decreases by 1/100. Scratch resistance was examined to clarify the dependence of pass wear durability on P_Ar, using a sapphire scratch needle. The scratch resistance is found to be determined by Young's modulus value for CoCrTa films. CoCrTa film flexible disk with high Young's modulus value has high pass wear durability. As the result of flexible disk environment tests, pass wear durabilities, more than 10 million passes, are confirmed under high temperature(60°C) and high humidity (80 %RH) condition, as well as low temperature (5°C) condition.

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  The influence of media defects on missing signal pulses was studied for a 3.5 inch single sided Co-Cr flexible disk drive. Most of the missing pulses were brought about by relatively large defects, which were induced during the deposition process of the Co-Cr and protective films. Small protuberances of the media due to the substrate film seldom induced the missing pulses. The head run on the top of the surface of the defects in contact. As a result, the defects had a tendency to be worn down and became flat, but the wear rate was extremely slow, different from the case of small protuberances. The wear rate for a defect in a thin film medium depended on, first, the head surface condition, second, the size and shape of the defect. The authors confirmed the possibility of defect burnishing without leading to serious problems.

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  Both axial runout and signal durability of a Co-Cr/Permalloy flexible disk with diameter 3.5", were studied using a disk drive with a pair of pads arranged in series relative to the disk radial direction, and with a single-pole type head.
  In the drive, the radial position of the head was 35 mm at disk revolution rates ranging from 600 to 1200 rpm, to evaluate the effect of the pad configuration on the runout characteristics and read-write properties. The runout of the disk were suppressed less than 10 μm, and frequency spectra of the suppressed runout were observed up to 2 KHz. Stable read-write characteristics of the disk were observed in the high-density region over 70 kfci under a head pressure of about 3 mN and runout of less than 10 μm.
  An out-put signal loss over 70 kfci was less than 1 dB after 7 million times of the head passes. No scrutches were observed on the disk surface and the head-pad sliders after the durability test.

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  A new slider called a main-pole protruding slider (MPP slider) has been developed for high-density recording of a flexible disk. The MPP slider has a very small slider/medium spacing of about 500Å independent of the disk velocity. When a CoCr/NiFe sputtered perpendicular-recording flexible disk is used, the MPP slider can stably run under a small load of 5g, even though the contact point may fluctuate due to the curl or undulation of the medium. Therefore, scratches are rare.

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  We have investigated the durability of Fe-Co-O/Fe-Co double-layered perpendicular magnetic recording media. It was found that the generation of microscopic surface cracks caused by internal stresses in the Fe-Co-O layer is suppressed by introducing an Fe-Co underlayer, suggesting that the Fe-Co layer acts as a stress absorber. It was also found that the Fe-Co-O/Fe-Co medium showed a compressive stress state. Stress in the medium, however, was reduced by the introduction of a Cr layer sputtered on a polyimide substrate, showing a tensile stress state. A medium with lower internal stresses showed higher durability. This result suggests that the durability of the medium depends mainly on fatigue caused by the internal stresses. Thus, an Fe-Co-O/Fe-Co/Cr triple-layered flexible disk medium with low stresses has shown excellent durability for more than 10 million passes without a protection layer.

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  Tribological phenomena of CoCr tapes and ferrite heads on VCR are not well known. The wear characteristics of ferrites having some crystalline planes were investigated by a new technique of wear volume measurement. It was found that (211) plane shows an extraordinarily anisotropic wear behavior in which two anti-parallel directions of ‹111› axis have wear rates which differ by the order of two. Consequently, the improper use of (211) sliding surface as a magnetic head was shown to result in a change of head contour and poor gap precision through sliding with CoCr tape. Coating of the CoCr tape with the diamond-like-carbon thin film was effective to nullify this anisotropic wear characteristics.

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  A high capacity (greater that 2 GB unformatted) disk drive has been developed, using perpendicular recording components. The drive is based on a 200 mm rigid disk format. The drive mechanics are conventional, using a rotary actuator for the head carriage; the disk rotational velocity is 3600 RPM. The high capacity is achieved by using the high resolution and the high signal amplitudes made possible by the perpendicular recording technology. The disks used are double-sided, each with a double layer (permalloy underlayer, CoCr storage layer) on conventional aluminum substrates. The heads consist of a thin-film probe element, a 4-layer 50-turn coil set, and a ferrite flux return element, mounted on a conventional Winchester-type slider. The heads operate with standard disk drive read/write electronics, previously developed for conventional thin-film inductive heads. The track width of the heads is 320 u", achieving a track density of 2100 TPI (with embedded servo). Linear density is nominally 16 KFCI, with a 2F/1F resolution in excess of 84%, enabling a (2,7) data compression code to be used, thereby achieving a linear bit density of 24 KBPI. The 50-turn head results in signal amplitudes in excess of 400 uV p-p at the inner radius. The well-defined magnetic width of the head also contributes to the attaining of these high track densities. In addition to this high level of performance, the design intrinsic to the perpendicular recording heads enable a much higher manufacturing yield than is currently attainable by alternative means to achieve these densities.

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  A waveform equalization technique suitable for perpendicular read/write channels with double-layered media and thin film heads is described. This equalization transforms a di-pulse waveform, which causes large intersymbol interference, into a single pulse waveform and then eliminates its sidelobes. Consequently, the intersymbol interference due to the unique waveform of this type of read/write channel is effectively reduced.

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  We have developed a thin film single-pole head/double-layer perpendicular media combination for rigid disk drive. It has many perfect performances and some unsatisfactory performances, there is a minor pulse in the read-back signal. The minor pulse is produced by the tail of ferrite slide which acts as a side pole. As recording density increases, adjacent pulses will close each other, and the minor pulse will be added to the adjacent main pulse, the asymmetry and the peak shift of the minor pulse will be aggravated. We use an equalizer to improve the read-back pulse with a minor pulse. The minor pulse is reduced. The read channel of longitudinal recording rigid disk drive is still suitable for rigid disk drive with single pole head/double layer perpendicular media if the equalizer circuit is modified.

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  In order to evaluate the perpendicular magnetic recording (PMR) technology from the viewpoint of computer system, a quantified relationship between the On-Line behaviour (OLB) of disk drive and its main preformance parameters is established. It is observed by this relationship that the extra-high bit dinsity potential is only one part of its advantages. Its potential on the improvement of OLB of disk drive might be of even greater importance.

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  A single-pole type perpendicular head with an Fe-Si/SiO₂ multilayered main-pole and a durable 3.5-inch Co-Cr/Ni-Fe flexible disk medium were loaded on an image file system constructed for trial. The digital recording of still-pictures was tried by guardbandless recording. Image data was successfully recorded and reproduced at the density of 82.5kFRPI/254TPI or 60kFRPI/508TPI with a bit error rate of 10^-6.

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