International Telemetering Conference Proceedings / October 30-November 02, 1989 / Town & Country Hotel & Convention Center, San Diego, California / In order to satisfy future instrumentation data recording requirements, the availability of high data rate recorders with long record times is most desirable. Also, assurance of commonality amongst the many users of these data requires that any system designed be compatible across the user data base. Hence, the American National Standards Institute (ANSI) has developed a tape format standard that will assure commonality and exchange of data in an acceptable manner. This standard also establishes data rate recording requirements using a commercially available media in cassette form that will satisfy the operational need. DATATAPE is developing a recorder system that will meet the ANSI requirements of the data format on tape, as well as the data rate and record times implied by the standard. This paper discusses the development of the tape format standard and the design of the system that will fully comply with the standard. Test data will be presented to verify system capabilities. Additionally, DATATAPE’s progress in developing a system that will comply with the similar Department of Defense (DOD) tape format Standard, MIL-STD2179, will be presented, along with a summary of DOD programs that require MIL-STD-2179 compliant recorder systems.

No description available.

No description available.

A Read-While-Write (RWW) operation for tape and/or potentially disk applications is needed in the following three cases: 1. High reliability; 2. Data servo systems; 3. Buried servo systems. All these applications mean that the read (servo) head and write head are operative simultaneously. Consequently, RWW operation will require work to suppress the so-called crossfeed field radiation from the write head. Traditionally, write-read crossfeed has been reduced in conventional magnetic recording heads by a variety of screening methods, but the effectness of these methods is very limited. On the other hand, the early theoretical investigations of the crossfeed problem concentrating on the flux line pattern in front of a head structure based on a simplified model, may not be comprehensive. Today a growing number of magnetic recording equipment manufacturers employ thin-film technology to fabricate heads and thereby the size of the modern head is much smaller than in the past. The increasing use of thin-film metallic magnetic materials for heads, along with the appearance of other new technologies, such as the MR reproductive mode and keepered media, has stimulated the need for an increased understanding of the crossfeed problem by advanced analysis methods and a satisfactory practical solution to achieve the RWW operation. The work described in this thesis to suppress the crossfeed field involves both a novel reproductive mode of a Dual Magnetoresistive (DMR) head, which was originally designed to gain a large reproduce sensitivity at high linear recording densities exceeding 100 kFCI, playing the key role in suppressing the crossfeed (the corresponding signal-noise ratio is over 38 dB), and several other compensation schemes, giving further suppression. Advanced analytical and numerical methods of estimating crossfeed in single and multi track thin-film/MR heads under both DC and AC excitations can often help a head designer understand how the crossfeed field spreads and therefore how to suppress the crossfeed field from the standpoint of an overall head configuration. This work also assesses the scale of the crossfeed problem by making measurements on current and improved heads, thereby adapting the main contributors to crossfeed. The relevance of this work to the computer industry is clear for achieving simultaneous operation of the read head and write head, especially in a thin-film head assembly. This is because computer data rates must increase to meet the demands of storing more and more information in less time as computer graphics packages become more sophisticated.

In this dissertation, a systematic modeling study has been conducted to investigate the microwaveassisted magnetic recording (MAMR) and its related physics. Two different modeling approaches including effective field modeling and recording signal-to-noise ratio (SNR) modeling has been conducted to understand the MAMR mechanism on segmented thin film granular medium. First the background information about perpendicular magnetic recording (PMR) and its limitation has been introduced. The motivation of studying MAMR is to further improve the recording area density capacity (ADC) of the hard disk drive (HDD) and to overcome the theoretical limitation of PMR. The development of recording thin film medium has also been discussed especially the evolvement of the multilayer composite medium. Since the spin torque oscillator (STO) is the essential component in MAMR, different STO structures have been discussed. The relation between STO setting (thickness, location and frequency) to the ac field distribution has also been explored. In effective field modeling, both head configuration and medium structure optimization have been investigated. The head configuration study includes the effective field distribution in relation to the fieldgeneration- layer thickness, location, and frequency. Especially an interesting potential erasure is detected due to the imperfect circularity of the ac field. Several approaches have been proposed to prevent the erasure. Meanwhile, notched and graded segmentation structure have been compared through effective field analysis in terms of the field gradient and track width. It has been found that MAMR with notched Hk distribution is able to achieve both high field gradient and narrow track width simultaneously. In recording SNR modeling, first the behavior of MAMR with single layer medium has been studied and three phases have been discovered. As proceed to the multi-layer medium, a practical issue which is MAMR with insufficient ac field power and high medium damping has been introduced. Since the fabrication of STO with high ac power is highly difficult, the issue has been investigated from the medium side which is through an optimized medium structure, the provided ac field can be utilized more efficiently. It has been found that more segmentation on upper part of the grain to fit the ac field yields more efficient ac field power usage. Following this scenario, the graded and notched segmentation structure have been studied in terms of SNR and track width. The traditional dilemma between recording SNR and track width in the conventional PMR is partially solve using MAMR with notched segmentation structure.

Powerful error-correcting codes have enabled a dramatic increase in the bit density on the recording medium of hard-disk drives (HDDs). Error-correcting codes in magnetic recording require a low-complexity decoder and a code design that delivers a target error-rate performance. This dissertation proposes an error-correcting system based on polar codes incorporating a fast, low-complexity, soft-output decoder and a design that is optimized for error-rate performance in the magnetic recording channel. LDPC codes are the state-of-the-art in HDDs, providing the required error-rate performance on high densities at the cost of increased computational complexity of the decoder. Substantial research in LDPC codes has focused on reducing decoder complexity and has resulted in many variants such as quasi-cyclic and convolutional LDPC codes. Polar codes are a recent and important breakthrough in coding theory, as they achieve capacity on a wide spectrum of channels using a low-complexity successive cancellation decoder. Polar codes make a strong case for magnetic recording, because they have low complexity decoders and adequate finite-length error-rate performance. In their current form, polar codes are not feasible for magnetic recording for two reasons. Firstly, there is no low-complexity soft-output decoder available for polar codes that is required for turbo-based equalization of the magnetic recording channel. The only soft-output decoder available to date is a message passing based belief propagation decoder that has very high computational complexity and is not suitable for practical implementations. Secondly, current polar codes are optimized for the AWGN channel only, and may not perform well under turbo-based detector for ISI channels. This thesis delivers a powerful low-complexity error-correcting system based on polar codes for ISI channels. Specifically, we propose a low-complexity soft-output decoder for polar codes that achieves better error-rate performance than the belief propagation decoder for polar codes while drastically reducing the complexity. We further propose a technique for polar code design over ISI channels that outperform codes for the AWGN channel in terms of error rate under the proposed soft-output decoder.

Low-density parity check (LDPC) codes have experienced tremendous popularity due to their capacity-achieving performance. In this dissertation, several different aspects of LDPC coding and its applications to magnetic storage are investigated. One of the most significant issues that impedes the use of LDPC codes in many systems is the error-rate floor phenomenon associated with their iterative decoders. By delineating the fundamental principles, we extend to partial response channels algorithms for predicting the error rate performance in the floor region for the binary-input AWGN channel. We develop three classes of decoding algorithms for mitigating the error floor by directly tackling the cause of the problem: trapping sets. In our experiments, these algorithms provide multiple orders of improvement over conventional decoders at the cost of various implementation complexity increases.Product codes are widely used in magnetic recording systems where errors are both isolated and bursty. A dual-mode decoding technique for Reed-Solomon-code-based product codes is proposed, where the second decoding mode involves maximum-likelihood erasure decoding of the binary images of the Reed-Solomon codewords. By exploring a tape storage application, we demonstrate that this dual-mode decoding system dramatically improves the performance of product codes. Moreover, the complexity added by the second decoding mode is manageable. We also show the performance of this technique on a product code which has an LDPC code in the columns.Run-length-limited (RLL) codes are ubiquitous in today's disk drives. Using RLL codes has enabled drive designers to pack data very efficiently onto the platter surface by ensuring stable symbol-timing recovery. We consider a concatenation system design with an LDPC code and an RLL code as components to simultaneously achieve desirable features such as: soft information availability to the LDPC decoder, the preservation of the LDPC code's structure, and the capability of correcting long erasure bursts.We analyze the performance of LDPC-coded magnetic recording channel in the presence of media noise. We employ advanced signal processing for the pattern-dependent-noise-predictive channel detectors, and demonstrate that a gain of over 1 dB or a linear density gain of about 8% relative to a comparable Reed-Solomon is attainable by using an LDPC code.

Shingled Magnetic Recording (SMR) has been recognised as one of the alternative technologies to achieve an areal density beyond the limit of the perpendicular recording technique, 1 Tb/in2, which has an advantage of extending the use of the conventional method media and read/write head. This work presents SMR system subject to both Inter Symbol Interference (ISI) and Inter Track Interference (ITI) and investigates different equalisation/detection techniques in order to reduce the complexity of this system. To investigate the ITI in shingled systems, one-track one-head system model has been extended into two-track one-head system model to have two interfering tracks. Consequently, six novel decoding techniques have been applied to the new system in order to find the Maximum Likelihood (ML) sequence. The decoding complexity of the six techniques has been investigated and then measured. The results show that the complexity is reduced by more than three times with 0.5 dB loss in performance. To measure this complexity practically, perpendicular recording system has been implemented in hardware. Hardware architectures are designed for that system with successful Quartus II fitter which are: Perpendicular Magnetic Recording (PMR) channel, digital filter equaliser with and without Additive White Gaussian Noise (AWGN) and ideal channel architectures. Two different hardware designs are implemented for Viterbi Algorithm (VA), however, Quartus II fitter for both of them was unsuccessful. It is found that, Simulink/Digital Signal Processing (DSP) Builder based designs are not efficient for complex algorithms and the eligible solution for such designs is writing Hardware Description Language (HDL) codes for those algorithms.

As cloud computing and massive-data machine learning are applied pervasively, ultra-high volume data storage serves as the foundation block. Every day, nearly 2.5 quintillion bytes (50000 GB/second in 2018) of data is created and stored. Hard Disk Drive (HDD) takes major part of this heavy duty. However, despite the amazing evolution of HDD technology during the past 50 years, the conventional Perpendicular Magnetic Recording (PMR), the state-of-the-art HDD technique, starts to have less momentum in increasing storage density because of the recording trilemma. To overcome this, Heat-Assisted Magnetic Recording (HAMR) was initially proposed in 1990s. With years of advancement, recent industrial demos have shown the potential of HAMR to actually break the theoretical limit of PMR. However, to fully take advantage of HAMR and realize the commercialization, there are still quite a few technical challenges, which motivated this thesis work. Via thermal coupled micromagnetic simulation based upon Landau-Lifshitz-Bloch (LLB) equation, the entire dynamic recording process has been studied systematically. The very fundamental recording physics theorem is established, which manages to elegantly interpret the previously conflicting experimental observations. The thermal induced field dependence of performance, due to incomplete switching and erase-after-write, is proposed for the first time and validated in industrial lab. The combinational effects form the ultimate physical limit of this technology. Meanwhile, this theorem predicts the novel noise origins, examples being Curie temperature distribution and temperature distribution, which are the key properties but ignored previously. To enhance performance, utilizations of higher thermal gradient, magnetically stiffer medium, optimal field etc. have been suggested based upon the theorem. Furthermore, a novel concept, Recording Time Window (RTW), has been proposed. It tightly correlates with performance and serves as a unified optimization standard, summarizing almost all primary parameters. After being validated via spin stand testing, the theorem has been applied to provide solutions for guiding medium design and relaxing the field and heating requirement. This helps solve the issues around writer limit and thermal reliability. Additionally, crosstrack varying field has been proposed to solve the well-known transition curvature issue, which may increase the storage density by 50%.

Filmes de ligas FePt com uma estrutura quimicamente ordenada Tetragonal de Face Centrada FCT (tipo L1 IND.0) e textura [001] apresentam anisotropia magnética perpendicular, alta coercividade e grande efeito Kerr polar magnetoóptico. Entretanto, filmes completamente ordenados são normalmente obtidos através de um processo de \"sputtering\" com deposições em altas temperaturas do substrato(T IND. S > OU =600 ºC) ou por pós-tratamento térmico em temperaturas maiores que 500 ºC. As pesquisas atualmente em desenvolvimento visam a obtenção dessa estrutura ordenada a temperaturas mais baixas, o que seria mais adequado para aplicações práticas dos filmes. Neste trabalho, procuramos as melhores condições para a preparação de filmes de FePt com a fase ordenada FCT(001) em reduzidas temperaturas. Investigamos a influência do método de deposição, temperatura do substrato, espessura do filme e tipo de substrato sobre o grau de ordem química e textura dos filmes de FePt e, consequentemente, sobre suas propriedades magnéticas. Os filmes finos de ligas Fe IND.xPt IND. x-1(com x = 50 at%) foram preparados por \"Sputtering Magnetron DC\", através de dois diferentes métodos de deposição: pelo usual de codeposição e pelo método de deposiçãO alternada monocamadas atômicas (DAM). Os filmes foram crescidos sobre substratos de SiO IND.2/ Si(100), Si(100) e MgO(100), com e sem uma camada \"buffer\" de Pt ( com espessuras de 50 1 766 nm), sob T IND. s variando de temperatura ambiente a 600 ºC. O \"buffer\" de Pt foi usado para permitir melhores condições para a indução de um crescimento \"epitaxial\" da ordenada fase FCT(001) nos filmes de FePt. Os resultados da caracterização estrutural e magnética realizados através das técnicas de Difração de RAios-X (XRD) e Magnetometria de Amostra Vibrante (VSM) mostram que os substratos de MgO São adequados para induzir um crescimento \"epitaxial\" de filmes de FePt ) com uma estrutura FCT e textura [001]. Entretanto, com o uso de um \"buffer\" de Pt otimizado (com predominante fase FCC(100)), pré-depositado sobre MgO, foram obtifos melhores resultados em termos de \"epitaxia\" conveniente para o ordenamento da estrutura cristalina, para os filmes de FePt preparados por ambos os métodos de deposição. Os resultados mostram também que o efeito de um crescimento \"epitaxial\" induzido varia com a espessura do filme. Em relação ao método de deposição, os resultados revelam a maior eficiência de método DAM em comparação com o métodos de codeposição para a preparação de filmes de FePt com a fase FCT(001), em temperaturas reduzidas (T IND.s < OU = 400ºC). Com o uso do método DAM, foi possível a obtenção da fase ordenanda FCT(001) em filmes de FePt crescidos diretamente sobre o MgO em T IND. s = 400ºC. Para filmes de FePt crescidos sobre Pt/MgO, a formação da fase FCT(001) foi verificada em T IND.s = 200ºC e um alto grau de ordenamento químico (S = 0,88) em T IND. s = 400ºC. Estudos de Espectroscopia de Absorção de Rios-X (XAS) também foram realizados. / FePt alloy films, with a chemically ordered face-centered-tetragonal FCT (type LI IND.0) structure and [001] texture, present perpendicular magnetic anisotropy, high coactivity and large polar magneto-optical Kerr effect. However, completely ordered films are usually obtained either by sputtering process at high substrate temperatures (T IND.s MAIOR IGUAL A 600°C) or by postanneling treatment at temperatures higher than 500°C. For technological purposes the preparation temperatures has to be as low as possible. In this work we have searched the more adequate conditions to preparation of FePt films with ordered FCT(001) phase at reduced temperatures. We have investigated the influence of deposition methods, substrate temperature, thickness of film, and type of substrate on the degree of the chemical ordering and preferred texture of FePt films and, consequently, on their magnetic properties. The Fe IND.xPt IND.1-x alloy thin films (with x SEMELHANTE A 50 at%) were prepared by DC Magnetron Sputtering, via two different deposition methods: a conventional code position method and an alternate monatomic layer (DAM) deposition method. The films were grown on SiO IND.2/Si (100), Si (100) and MgO (100) substrates, with and without a Pt buffer layer (thickness ranging from 50 to 76 nm), at T IND.s varying from room temperature to 600°C. The Pt buffer layer was used for obtaining better conditions to the induction of an epitaxial grown of FePt films with the ordered FCT(001) phase. The results of structural and magnetic characterization performed by X-ray diffraction (XRD) and vibrating sample magnetometry (VSM) show that the MgO substrates are adequate to induce an epitaxial growth of FePt films with a FCT structure and [001] texture. However, with the use of an optimized Pt FCC(100) buffer layer pre-deposited on MgO, the best conditions to an epitaxial induced growth were obtained, by both deposition methods. The results show also that the quality of the epitaxial induced growth depends on the thickness of the film. In relation to the deposition method in comparison to the code position method for preparation of FePt FCT(001) films, at reduced temperatures (T IND.s MENOR IGUAL A 400°C). With the use of the DAM method it was possible to obtain the ordered FCT(001) phase in the FePt film grown directly on MgO, at T IND.s = 400°C. For FePt film grown on Pt/MgO, the formation of the FCT(001) phase was verified at T IND.s = 200°C, and high degree of chemical order (S=0,88) was obtained at T IND.s = 400°C. X-ray Absorption Spectroscopy (XAS) studies also were done.