We present a scalable solution that enables a single mainstream hard disk drive (HDD) to simultaneously record and play back multiple real-time (RT) video streams, in addition to supporting non-RT PC-like applications. The solution is scalable to different types of disks, different numbers of streams with different bit rates, and various non-RT applications.

A new method for recording above 100 Gb/in.2 is discussed. We call this method “hybrid recording,” a form of thermally-assisted recording that combines thermo-magnetic writing and magnetic reading. In order to increase the stability of the recorded information, writing is carried out at an elevated temperature on a medium with a very high coercivity at room temperature. In our proposal write and read heads with extremely narrow trackwidths are used, so the trackwidth is not determined by the optical spot size and the written bits have a rectangular shape, in contrast to the schemes proposed by others. Preliminary experiments are shown. The applicability of today’s granular and MO type media for hybrid recording is discussed. It is calculated that hybrid recording on optimized media can give an increase of the areal density of a factor 2.9 in areal density or 7 dB (2.2×) medium SNR improvement in case of Poisson noise and 11 dB (3.4×) in case of transition noise. Practically a factor of about 2 in density is more realistic, pushing limiting densities for longitudinal recording to 100–200 Gb/in.2. Typical limitations at very high densities arise from heat dissipation in the head and thermal instability of the medium. Based on simplified model calculations including realistic limitations on medium, head and leads, and today’s practical limitations on electronics, comparisons are made between read heads containing a tunnel junction magnetoresistive (TMR) element and containing a giant magnetoresistive element with sense current in the plane (CIP-GMR) or perpendicular to the plane (CPP-GMR) of the sensor films. They show that the signal-to-noise ratio of TMR sensors for areal densities above 15 Gb/in.2 is not advantageous over GMR sensors with sense current in the plane as long as the junction’s tunnel resistance is not drastically reduced to below 10 Ω μm2. The CPP-GMR heads are disadvantageous with respect to CIP-GMR heads until the highest densities, 300 Gb/in.2, considered.

Thermally assisted magnetic recording is seen as a possible route to increased areal recording density while maintaining long information storage times. The term hybrid recording is often used since the technique involves a hybrid of a magnetic and an optical recording system. In this paper we first discuss the recording system, thereafter we present our first recording results performed on conventional longitudinal thin film media. Finally the results are discussed and a direction may be inferred for the development of thin film media to take full advantage of thermally assisted magnetic recording.

DigaMaxTM thin film heads have been used with advanced tapes to estimate the performance improvement that is possible with respect to Co–γFe2O3 900Oe coercivity tape. The use of high sensitivity magneto-resistive read heads allows signal and media noise measurements at relatively low tape speeds with minimal interference from the electronics noise. This measurement method shows that although the absolute signal from advanced tapes has increased tremendously in recent years, the signal-to-media noise ratio has increased at a much smaller rate. Nevertheless, the best commercial metal evaporated tape of today shows a 4–5dB improvement in signal-to-noise ratio when compared to 900Oe tape.

Based on model calculations a comparison is made between yoke-type read heads containing a tunnel junction magnetoresistive element (TMRE) and containing a giant magnetoresistive element (GMRE). For typical head design parameters, TMR-based heads are 3-5 times more flux-efficient than GMR-based heads. However, for approximately 1/spl times/1 /spl mu/m/sup 2/ elements, the SNR of TMRE-based heads is not advantageous as long as the junction's tunnel resistance is not drastically reduced below R=1 k/spl Omega/.

The multichannel servo writer and the data read/write heads of the new DigaMaxTM tape storage system are discussed. These heads enable a storage capacity of 13 GB (uncompressed) on 300 m of 72 kA/m tape using prerecorded buried servo information for dynamic track following during reading and writing of data

A brief discussion of the differences in two generalized slope models suitable for modeling metal evaporated tape is presented. The inclusion of idealized correlations between the sublayers in one of the models is proposed as an explanation for the differences in the predictions of these models. The correlations appear to mimic the effect of strong magnetic interactions that are thought to be present along the oblique easy-axis direction in metal evaporated (ME) tapes.

The results of experimental and theoretical studies of nonlinear transition shift (NLTS) in advanced metal evaporated (ME) tape are noted. Using the harmonic elimination technique the NLTS as a function of linear recording density was measured. Using a calibrated self-consistent recording model the patterns corresponding to the harmonic elimination technique were simulated allowing NLTS to be calculated. Dipulses were also calculated, and carefully fitted, allowing Partial Erasure (PE) to be determined. The variation in NLTS as a function of easy-axis angle in ME tape was also simulated. In agreement with a previous conjecture by J. Mallinson [1989], the NLTS is found to go through zero, For the head and medium considered, the zero occurs at an easy-axis angle of slightly greater than 35 degrees from the longitudinal direction.

This work gives details of a quantitative recording model for magnetic media with arbitrary easy axis orientations. The model uses an iterative analytical approach to study variations with depth into the media allowing the investigation of thick and multilayered media, thereby extending the work of Williams and Comstock which applied only to very thin media. Using typical values for the head and medium interface, the model presents quantitative accuracy when compared with experimental data in both the frequency and time domains for metal evaporated (ME) tapes while using the minimum number of adjustable parameters.

The performances of digital magnetic recording systems using peak detection are shown to be described by equations that involve parameters and variables which occur in ratios. Provided that these quantities vary in proportion there is no change in system performance. Thus scaling of one parameter shows how scaling of another leads to a system of unchanged performance. It is further shown that the influence of a wide range of values of parameters on system performance can be accounted for by a limited range of computations. Results are given for media and systems of high performance which arguably represent the current state of the art and possible future aspirations.

The results of experimental and theoretical studies of nonlinear transition shift (NLTS) in advanced metal evaporated (ME) tape are noted. Using the harmonic elimination technique the NLTS as a function of linear recording density was measured. Using a calibrated self-consistent recording model the patterns corresponding to the harmonic elimination technique were simu- lated allowing NLTS to be calculated. Dipulses were also calculat- ed, and carefully fit, allowing Partial Erasure (PE) to be determined. The variation in NLTS as a function of easy-axis an- gle in ME tape was also simulated. In agreement with a previous conjecture by J. Mallinson, the NLTS is found to go through zero. For the head and medium considered, the zero occurs at an easy- axis angle of slightly greater than 35 degrees from the longitudi- nal direction.

Models of the digital recording characteristics of metal evaporated tape based on developments of ‘arctangent’ theory and from a micromagnetic standpoint are reviewed. It is shown that the former predict observed recording properties with good accuracy although micromagnetic calculations indicate some shortcomings in the basic assumptions of that theory.

A model is presented which enables the recording properties of media with arbitrary easy magnetisation directions to be studied. The slope theory of Williams and Comstock is extended to give a model using three parameters: the transition location, the transition width and the magnetisation in the medium. Results of simulations are presented as a function of the easy axis angle for fixed write current, and for write current optimised at each easy axis angle. Isolated pulse waveforms and close-packed pulse outputs are predicted and show the general features observed including asymmetry when using media with tilted easy axes such as metal evaporated (ME) tape.

The output voltage waveforms expected when replaying with various head structures from media magnetized in arbitrary directions are predicted. Expressions are given in useful closed forms for the outputs in isolated and pulse crowded circumstances. Output waveforms are shown for a range of orientations of the recorded magnetization to reveal aspects of pulse symmetry and their effects on ''roll-off'' curves.