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A new D-VHS system developed on the basis of the VHS video tape recording format has been developed for recording digital data compatible with digital broadcast systems. The system can handle a variety of digital formats to meet the diverse needs of multimedia applications.

Aggressive track-density scaling in linear magnetic tape recording has been identified as a key means of sustaining capacity scaling. As the reader width decreases, the relative signal contribution of the written track region outside the lateral extent of the reader increases. We model, analyze and quantify side-reading effects of shielded magneto-resistive read heads reading narrow tracks on perpendicular-oriented tape media. We compare results from extended analytical models with experimental data. An understanding of these effects will be important in designing track misregistration budgets and SNR margins for future operating points of parallel-channel tape recording systems.

A tape recording head in which reading and writing functions are provided by separate modules is presented. The read-only module may be fabricated with a thinner gap than conventional read-write modules. This was shown to provide >; 40% less gap recession in a controlled wear test. Writing modules are configured to contact tape in one tape motion direction only, thus reducing the wear duty cycle twofold. Modeling indicates that broadband signal-to-noise ratio decline due to wear can be up to several dB less for the separated reading-writing head, which therefore may enable advances in linear and thus areal density.

Local microscopic particle density variation stemming from packing density far below unity is one of the important aspects of digital tape recording. In this paper, we present a modeling methodology for simulating realistic particle packing in particulate tape media. The packing algorithm is able to generate randomly dispersed tape particles with packing density as high as 34%-40% and user-defined parameters such as easy axes orientation, aspect ratio variation, size distribution, etc. Micromagnetic modeling of recording characteristics have also been conducted to study the impact of various aspects of packing.

We present a planar thin-film servo write head for writing timing-based servo patterns. The planar head operates at low current ( ~ 100 mA) with nanosecond switching times. The planar head can handle dc current, enabling trailing-edge writing. Magnetic force microscopy measurements of the transitions written by the planar head and a conventional commercial servo write head on longitudinal metal particle and nonoriented barium ferrite media were made to assess the quality of the written transitions. The transition response width PW50 is found to be independent of the tape velocity during write for the planar head. For the conventional head, PW50 is larger and increases with the tape write velocity. The reduced PW50 results in larger readback signal amplitude and hence an improved track-follow performance. The faster switching capability of the planar head enables formatting at higher tape velocity.

This paper reports on a corrosion-resistant spin-valve head (Ta/NiFe/CoNiFe/CuAu/CoNiFe/PtMn/Ta) for a tape recording system. The spin-valve film has a +0.4 V higher electrochemical potential than the conventional spin-valve film (Ta/NiFe/CoFe/Cu/CoFe/PtMn/Ta). The spin-valve head with CoNiFe magnetic layer and CuAu spacer exhibits good corrosion resistance. An investigation of the recording characteristics of the corrosion-resistant spin-valve head with metal evaporated (ME) tapes showed that: 1) the spin-valve head had about 64% of the output voltage of an isolated pulse of the conventional spin-valve head; 2) the carrier-to-media noise (C/N/sub media/) ratio at a wavelength of 0.4 /spl mu/m of the spin-valve head is the same as that of the conventional spin-valve head; and 3) the C/N/sub media/ ratio of thin ME tape with magnetic layer 33 nm thick was maximized at around M/sub r/t=10 mA, where M/sub r/ is the remanent magnetization and t is the magnetic layer thickness. These results indicate that the corrosion-resistant spin-valve head (Ta/NiFe/CoNiFe/CuAu/CoNiFe/PtMn/Ta) for a tape recording system provides high recording density.

A recently developed, advanced multi-track tape head for operation in a next generation, high performance tape drive is described. This head features full thin film write elements with high moment, cobalt-based pole materials for recording on high coercivity metal particle (MP) tape, together with narrow track, shielded, dual-stripe magnetoresistive (DSMR) read elements. This presentation will discuss the global design philosophy of the head with particular attention to the design and recording performance of the read and write elements in a tape environment. The bead is capable of recording 288 tracks on half-inch, MP tape of 1625-1850 Oe coercivity at a recording density of 65 kfci. The system operates with 16 parallel data channels and includes full multi-element active track following servo. The head can be used in a full start-stop mode and read verify on the fly (read-while-write) bi-directional operating modes.

In this paper we present results on the fabrication and testing of thin film tape recording heads using high moment FeAlN pole materials (4/spl pi/M/sub s/=20 kGauss). These heads are of the type used in quarter inch cartridge (QIC) tape drives, with a record gap dimension of 1.9 /spl mu/m and a written track-width of 33 /spl mu/m. The pole thicknesses ranged from 4 to 4.5 /spl mu/m with a 14 turn coil. The FeAlN pole material delivers sufficient field to the media surface to saturate 1.5 /spl mu/m thick Ba-Ferrite media (H/sub c/=1500 Oe). In comparisons to a head of identical design with CoZrTa poles, the FeAlN poles were able to deliver more flux to the media because of a higher head saturation onset current.

A simplified vector field model is used to analyze isolated pulse asymmetry, input/output curves, nonlinearities in dibit recording, and overwrite for thick longitudinal tape. The recording layer of a well oriented medium is discretized into laminae, and the magnetization transition parameter and phase in each lamina are determined by both the vector head field and vector demagnetizing field. Typical head-medium spacing is considered as well as imaging of the demagnetizing fields by the record head. A significant magnetization transition phase shift and an increasing transition length with depth into the media are produced by the demagnetizing field, which plays a central role in explaining the phenomena of high density tape recording. Both pulse asymmetry and nonlinearities increase with demagnetizing ratio 4/spl pi/M/sub r//H/sub c/. The signal voltage increases with bit length and decreases with the demagnetizing field in agreement with experiment. Overwrite for fixed frequency improves for larger deep gap field until the head field to coercivity ratio H/sub g//H/sub c/ reaches 3.5 and then subsequently decreases, for typical head-medium spacing d/g=0.25 and 4/spl pi/M/sub r//H/sub c/=2. 2F/1F overwrite maximizes when the bit length of the 2 F signal equals the gap length in agreement with measurement. >

A self-consistent micromagnetic recording model is utilized to study the effects of write head field rise time in tape recording. It is found that fast speed and slow field rise time result in degradation of recording performance for both nonequalized and write equalized cases. It also suggests that D=T/2 scheme could be more suitable than the D=T/3 scheme in write equalization at high speeds.

In guardband-less tape recorders, azimuth recording is commonly used to reduce intertrack interference. Previous work on the optimization of the azimuth angle for digital recording [1] uses the criterion of minimum on-track bit error rate (BER). In this article, we consider the maximum tracking margin to be a more relevant criterion. Furthermore, the calculation model in [1] is extended to cover a wider range of equalization and detection schemes, including the increasingly popular partial response Class IV equalization with Viterbi detector (VD). The gain of using VD over the conventional threshold detection is also discussed. BER measurements on several recorders with different geometrical configurations serve to verify the validity of the calculation results. >

Nonlinearities in high-density tape recording have been studied. Dibit responses were measured versus recording density and write current. The dibit responses were then compared to the linear superposition of isolated transitions. It is shown that nonlinear bit shift and transition width changes are required to explain the differences. These nonlinear effects can be parameterized for signal processing purposes using the pulse response by including a timing shift and a time scaling for the second pulse response in a dibit. These parameters explain the observed difference between square-wave spectral response and isolated pulse FFT. A simple technique for obtaining head efficiency, the effective head-medium spacing, and the depth of recording is presented. >

An image coding algorithm for digital video tape recorders (DVTR) must satisfy several requirements which do not arise in other applications of video compression. A key constraint on the data format is satisfied if every frame (or field) of video is partitioned into a small number of subimages, each independently coded with a fixed number of bits. This requirement excludes the use of interframe coding and most variable-rate image coding algorithms. We propose to use a new algorithm that codes a subimage efficiently under this data format constraint and allows virtually lossless reproduction at reasonable low bit rates. Each subimage is partitioned into non-overlapping blocks and each block is coded by one of a finite set of predesigned block quantizers covering a range of bit rates. For the ith block in the subimage, a rate function Ri(Li) and a distortion function Di(Li) is tabulated for each block quantizer Li. A near-optimal quantizer allocation algorithm based on the Lagrange Multiplier method is used to select a particular quantizer for each block. The objective is to minimize the distortion of the entire subimage under the constraint on the total number of bits for the subimage. A system for the compression of HDTV for DVTR's based on this rate-constrained optimal block-adaptive technique is designed using the DCT and vector quantization with a multistage structure. Simulation results demonstrate that this algorithm has the potential of achieving virtually lossless compression for digital tape recording of HDTV.

In this paper, we compare experimental measurements of magnetic tape recording signals with the results of simulation. Specifically, nonlinearities associated with the write equalization process are examined. It is found that the depth dependent vector Preisach model (VPM) of the magnetic recording process is able to semi-quantitatively reproduce nonlinearities that are seen in the readback from real heads and media. The failure of standard linear superposition models even qualitatively to capture these effects is demonstrated. Furthermore, the VPM shows, through the recorded magnetisation distribution, that demagnetizing effects from the data transitions can distort the write equalization pulses, if the pulses follow the data transitions too closely. This leads to a directional asymmetry in the writing process, such that symmetrically placed write equalization pulses do not lead to the most symmetrical waveforms.

A self-consistent recording simulator combined with a micromagnetic MR head model is developed to study write equalization in tape recording. The simulation study presented in this paper focuses on the understanding of the magnetization configurations resulted from write equalization and the impact on the write and read nonlinearity. It is found that the write equalization process results in a demagnetized state in otherwise saturated regions. The model analysis combined with an EPR4 channel demonstrates how both write and read linearity of the system are improved.

In this work, the performance of a narrow track MR head/MP tape recording system was evaluated focusing on the MR head saturation. Readback density of 0.65 Gbits/in/sup 2/ was attained with reasonable SNR of 18.2 dB using a 5 /spl mu/m trackwidth MR head and thin layer MP tape. Saturation at low densities was suppressed by the selection of a run length limited 8/10 modulation code. This result suggests that the excellent performance of the narrow track MR head could increase areal density in tape recording, and would steer the development of particulate tape media toward reduction of magnetization thickness product and improvement of media noise characteristics.

In conventional recording, tape wraps a cylindrically contoured head. The authors describe an implementation in which tape contacts a flat-profile bidirectional recording head. Magnetic transducers are located away from the air-scraping edges in the region of uniform head-tape spacing. Optical measurements on glass heads confirm intimate contact between head and smooth media below approximately 3 m/s. Wallace spacing losses show an increase with tape speed, but contact is still evidenced by head wear at 6 m/s. Air leakage and tape mechanical effects lift the tape edges. The width of the lost-contact region is controlled by the design. Flat heads are fabricated using hard-disk-drive head materials, methods, and facilities, and are implemented in the IBM TotalStorage 3580 Linear Tape Open Ultrium drive.

In this paper, an analysis technique is presented for block oriented data formats in digital tape recording systems. The approach determines format parameters that maximize the information storage density at a specified failure rate. In the process, it is also shown that block interleaving is not beneficial for many systems.

The mechanisms of pulse asymmetry and nonlinearities in dibit recording have been analyzed by numerical simulation. Well-oriented longitudinal tape media were modeled by 2D discretization and subsequent iteration including distributions in particle orientations and intrinsic switching fields. Typical head-medium spacing was included as well as imaging of the demagnetization fields by the record head. Isolated transitions and dibits were recorded utilizing head fields typical of high-density recording. Characteristic isolated pulse asymmetry is shown to be due predominantly to the demagnetization fields during the write process which substantially shifts the phase of magnetization transitions with depth into the medium. In dibit recording with optimum or greater record currents, the second transition is shown to yield a larger playback voltage than that predicted by linear superposition. >

Aggressive growth in cartridge capacity in future generation tape drives requires amongst others, high linear recording and track densities. In order to improve the track misregistration (TMR) budget at smaller track pitches, the erase band and tolerances on the recorded track width need to be minimized. This can be achieved by "trimming" the write element to the desired track width by forming a longitudinal channel on either side of the clement on the tape bearing surface (TBS) using focused ion beam (FIB) milling. Cross-track measurements depict desired track widths with reduced forward-reverse track width asymmetry in the read-write-read head configuration. Investigation of the head/tape interface does not predict any undesirable effects. These channels capture debris and hence will reduce the recording loss, especially at higher linear recording densities, due to tape tenting over loose debris transported through the interface and near the recording elements. A conceptual channel design is presented that will further reduce debris near the recording elements during the life of the head.

A general solution of digital recursive filters which produce two-level output is given. To give a rough idea of the performance of write equalizers, a high-density recording channel corrupted by additive noise is appraised, and the signal-to-noise ratio with and without a write equalizer is compared. Calculations show that a small gain can be expected in using some of the write equalizers. The linearity of the channel was tested using some of the write equalizers. >

A plain flat 'row-bar' of commercial thin-film disk heads was evaluated and found to be suitable for high speed and high track- and linear-density tape recording. After more than 2000 hours of running in contact at 8 m/s no output degradation was observed. An upper limit of 4 nm was placed on head wear. Output, hence head-tape spacing was seen to be independent of the tape speed from 0.5 to 8 m/s. A mechanical model of the system shows that a self-acting negative air bearing (suction) is responsible for the stability of the interface.

This paper reports experimental results of a comparative study for mechanical and tribological properties of permalloy (NiFe) and magnetically soft high moment FeTaN sputtered thin films. It was observed that the hardness, elastic modulus and wear resistance of FeTaN films are all superior to those of NiFe permalloy films. AFM observations on unworn films and worn surfaces of a wear scar revealed that pit formation may contribute to wear damage mechanisms for low load abrasive wear.

Improvements to a method of calibrating a high-density tape recording system are suggested. The small gap approximation is not made, and allowances for the effects of demagnetization are included. A better and smaller estimate of the effective head-media spacing is obtained. >

The effect of head saturation on the signal spectrum in high-density tape recording has been investigated using a simple model for the recording process and a finite-difference model for the head. Phase relationships in the recording process are incorporated by utilizing the angularly dependent switching behavior of a two-particle simplified system. The recording process under saturation is shown to depend on the achievable deep gap field since the head field shape changes only slightly. Scanning-Kerr-microscope assessment of saturation is shown to differ from that of a micro-loop. >

The authors report data comparing a shielded magnetoresistive head (SMR) optimized for metal particle tape readback to an unshielded head (UMR) with an identical element. They identify the signal-to-noise ratio penalty for eliminating the shields as a function of tape velocity and data density. They report on the degree of nonlinear distortion for UMR and SMR heads with and without write equalization. From these experiments the performance of an element optimized specifically for the absence of the shields is predicted. An unshielded sensor can be a satisfactory replacement for an SMR sensor at linear densities up to 2500 fr/mm, provided it is redeveloped for optimum signal amplitude and linearity. >

Since the first commercially successful video tape recorder (VTR) was developed in 1956, the rotating-head-type VTR has been the mainstream of video recording. In the rotating-head-type VTR, the shorter recording wavelength makes possible a smaller and better cost-performance VTR for institutional and home use. The reduction in the recording wavelength on the recording media has been mainly accomplished by the improved developments of video head and tape. Depending upon international communications and business activities, a global VTR system for NTSC, PAL and SECAM is expected, and the VHS format VTR is the only system to meet with simple modification, this requirement at present. The video software business will become more active when the VTR population increases to a certain number, such as a million. Contact duplication technology will become very important to meet this market demand. The Bifilar winding method is presumed to be a commercially successful way for mass duplication of video tapes in the near future. The historical background of these subjects and future forecasts are discussed in this paper.

An analysis of the magnetic tape recording process employing supersonic excitation is presented by considering the effect of the spatial distribution of the magnetic field around the recording head air gap on the magnetic history of an unmagnetized element of tape as it tracks across the recording head. This leads to an effect which is termed "recording demagnetization" and serves to explain certain performance characteristics. An experimental technique developed for the measurement of this recording demagnetization is described, as is the method of measuring the air-gap field distribution. Finally, the correlation of the measurements of the recording demagnetization with normal recording performance characteristics is reported.

The responses to a mail survey of 2735 broadcast and television stations were analyzed to determine the extent to which tape recording is presently used in routine broadcasting.

A method of measuring drop-outs from magnetic-tape recording systems has been designed and built so that quantitative data can be quickly obtained from any tape on any machine and under any condition. Conclusions are made as to the relative effects of tape, machines, reels, recording processes, reproducing processes, environmental dirt, tensions, etc., on the drop-out count. It has been found that drop-out measurements can be used to evaluate tape and machines in regards to wear characteristics, to evaluate tape-cleaning methods, and to determine techniques in handling tape and operating tape machines to minimize drop-out effects both for analog and digital applications.

The search for a reliable encoding and decoding process for pulse-code modulation (PCM) data streams is discussed with application in both the serial and parallel mode employing standard IRIG wide-band (2.0 MHz at 120 in/s) longitudinal magnetic tape recorder/reproducer. Serial and parallel PCM data at 4.0 and 3.0 Mbit/s/track, respectively, may be handled by the Sangamo Electric Company instrumentation systems with PCM channels in both portable and laboratory configurations. Not only was a method identified to utilze the maximum bandwidth available in conjunction with acceptable data error rates, but definite advantages and disadvantages were verified for all the standard PCM formats.

Mechanisms of the generation and the control of magnetic head noise in an audio tape recorder were studied. Head noise was generated from some flux changes by 180° domain wall movements which were produced because of relaxation of shocks given by a frictional vibrating tape. Then noise spectrums were based on vibration spectrums of a tape. Low noise property of a permalloy head was due to large eddy current losses which were accompanied by restrictions of domain wall movements. On a ferrite head noise, effects of crystalline anisotropy and distortion were great, however, a low noise ferrite head was not presented until shape anisotropy and pinning effects by the grain boundary or SnO 2 precipitation were applied.

MOTION PICTURES have obviously required synchronized sound to match picture and words in all released prints. Perforated film has been the usual answer to this requirement ever since sound was added on film. But now that magnetic recording has shown such tremendous opportunities in quality and economy, the use of this facility for sound for motion pictures is immediately attractive. One answer has been, of course, the use of normal photographic film stock, coated however with iron oxide instead of the usual silver emulsions. And again perforations accomplished the lock-in. But 1/4-inch tape without sprocket holes is so much more flexible because of its thinness, takes up so much less space, and gives top quality with so little effort that its use would certainly be ideal if synchronism might also be accomplished.

A comparison is made of the performance of magnetic tape when the recording field is in the same direction as, or perpendicular to, the oxide particles as encountered in magnetic disc or video recording.

The design criteria for magnetic recording tapes are considered with respect to the desirable physical and magnetic characteristics for high-resolution recording systems; in particular, the magnetic properties of the universally used iron-oxide powders are compared with possible competitive permanent magnet materials. The properties of oxide and metal powders and of metallic thin films are compared, and the possibility of their future use in high-output high-resolution tapes is also assessed in this paper.

Standard designs are flexible enough for most uses of tape recorders. Special machines have been devised for unusual applications such as pronouncing dictionaries, length measuring devices, time compressors, dc and square wave recorders, memory devices, and automatic machine control. The construction and operation of typical devices are reviewed.

The conditions under which linear superposition (LSP) of isolated pulses is valid for the synthesis of multibit waveforms are examined theoretically. LSP is found to be valid subject to three conditions; first, that all the processes following the write process be linear operations on the tape magnetization; second, that the write field rise time be less than the bit interval; and third, that each change in magnetization, occurring during the write process, be a function only of the field causing that change. Additionally, the validity of LSP at 15 000 bit/in is demonstrated for a high resolution tape recorder using standard γ-Fe 2 O 3 tape.

This paper is concerned with experiments that were run for the purpose of supporting or discounting the various alternating current bias theories concerned with direct recording onto magnetic tape. Only the theories of Toomin and Wildfever, and Camras were found to be compatible with the results.

The primary object of the work described here was to determine what properties of the tape and associated magnetic elements are responsible for the noise and signal output levels of magnetic recordings and, if possible, to display in specific equations the pertinent relation-ships connecting noise and signal levels with the physical properties of the tape and polepieces. In the course of the study, methods appeared for decreasing the noise and increasing the useful signal reproduced from magnetic tape. These methods and some of the use that Bell Telephone Laboratories and Western Electric have made of them are mentioned in the discussion. While some of the work described in this paper has implications for more than one type of magnetic recording process, perpendicular recording on tape1 is the actual subject matter dealt with. In every case discussed, the record medium was 0.050 inch wide and 0.0022 inch thick. Except where otherwise noted, a chrome-steel tape was used at a speed of 16 inches per second.

A number of methods for azimuth alignment were investigated. A technique for alignment which compares the output from two tracks of a multitrack tape provided a substantial improvement in alignment accuracy as compared to the methods which had been in use up to this time. A method for adjusting the lateral position of the head across the width of the tape was also developed which made use of the same basic principles as the "null method" of azimuth alignment.

ONE of the most pressing problems in modern life is the construction and maintenance of an adequate system of highways. It is evident that the need is great for more new highways and, equally important, they must be constructed in the most durable manner possible.

This paper examines the influence of magnetic tape, read-write head, and other recording parameters on peak shift encountered in high-density recording. In particular, the effect of prior erase polarity on peak shift is discussed. A technique for examining the remanent moment in a sample of the recorded tape track as a function of write current, density, and angle from the plane of the oxide coating is described.

Future tape recorders running at a speed of 1\frac{7}{8} ips must achieve an upper frequency limit of 15 kc on a quarter track recording, with better SNR than presently obtained with commercial recorders. This means that the subjective quality of present full track machines at 15 ips must be maintained in spite of a fifty-fold increase of information density. It is obvious that such an improvement cannot be obtained only by changes to the electronic circuitry and the like. In fact, the future requirement would be impossible to meet if improvements in tape and heads were not made. Such improvements must include new knowledge of head construction, tape-to-head contact problems, and optimum balancing of recording parameters. But once these improvements are effected, it is then necessary to check carefully if the most thorough use is being made of all available technical possibilities. It will be shown that recording techniques have advanced to a stage where a change in the standardization characteristics is advantageous and even necessary, though they may be more complicated than the existing standards.

Co-P thin film is promising as a high density recording medium. It has been used in magnetic drums and disks, but no report has been published on its use for a conventional VTR. Therefore, we have been studying its possible application to video tape. This paper introduces our experimental plated Co-P tape for a conventional home VTR. For additional details, see Digests of the 1972 Intermag Conference (available from IEEE Headquarters).