Magnetic Tape Storage System Research Articles

Development of Large Capacity Magnetic Tape Storage System

1．はじめに

Adaptive noise-predictive maximum-likelihood (NPML) data detection for magnetic tape storage systems

Advanced data detection will be one of the key enablers to achieving the very high areal recording densities of future tape storage systems. Departing from the partial-response maximum-likelihood (PRML)-based read channel design traditionally used in tape systems, this paper describes noise-predictive maximum-likelihood (NPML) detection, which is a technique that has been known for many years in the hard-disk-drive industry but has been introduced for the first time in the tape storage industry in IBM tape drives. In the NPML read channel design, the readback signals are conditioned prior to data detection so that their noise components are statistically decorrelated and reduced in power. This paper describes the basic principles of NPML detection and its application to tape systems in the form of a 16-state detector. It is argued that, because of the inherent variability of the recording channel characteristics in tape drives, fully adaptive NPML detection needs to be realized in order to optimize detection performance. Actual readback waveforms of data recorded on metal particulate as well as barium-ferrite particulate tape media are used to illustrate the error rate performance achieved by 16-state and 32-state NPML detectors. It is shown that, under realistic worst-case channel conditions, a 16-state NPML detector could offer an improvement in error rate after an error-correcting code of approximately two orders of magnitude.

Frequency domain subspace identification of a tape servo system

As capacity demands for magnetic tape storage systems grow, servo actuator design for tracking data on high density tape media presents new modeling and control design challenges. In this paper a frequency weighted subspace identification algorithm is presented for control relevant model estimation of a tape servo actuator. Common to other subspace identification methods, the proposed algorithm is based on linear algebra techniques providing means for model order selection and model computation. The proposed subspace identification also allows for frequency dependent weightings to emphasize frequency data around the cross-over frequency to find models relevant for control design. The algorithm is applied to data obtained from a tape storage device, demonstrating model order selection and the estimation of servo actuator dynamics with control relevant model fit criteria.

THE SOURCE OF FIVE-MINUTE PERIOD PHOTOSPHERIC UMBRAL OSCILLATIONS

ABSTRACT Many types of velocity oscillations are observed in the umbrae and penumbrae of sunspots. We describe a project aimed at determining the source of one type of oscillation, the five-minute period photospheric umbra oscillations. The project uses imaging spectroscopy of spot umbrae, measuring the Doppler shift of pure umbral absorption lines to study the temporal and spatial properties of these oscillations. The Mees CCD (MCCD) instrument is an imaging spectroscopy device which uses the 25-cm coronagraph telescope and the 3.0-m coude spectrograph at Mees Solar Observatory (MSO) on Haleakala, Maui. The instrument works with resolving power up to R ~ 200,000 with significant throughput from lambda-3934 A (Ca II K) to lambda ~ 10,000 A. A fast guiding active mirror stabilizes the image during observations. A rapidly writing magnetic tape storage system allows observations to be recorded at 256 kbytes s-1. We observed the oscillations in the umbrae of two sunspots using the MCCD imaging spectrograph. We observed the Doppler shifts of 18 molecular lines in the umbrae for roughly 50 hours in each spot during the interval of 11 to 16 May 1991. We find no simple correlation between the velocity measured with molecular lines and the velocity measured using two iron lines. We remove solar rotation, image drift, and interpolate all the data onto an even time grid. We perform four spatial analyses of the umbral velocity and find (1) there is more power traveling toward the center of the umbrae than leaving the center of the umbrae (this provides a direct measure of the absorption of p-modes by the sunspot umbrae) (2) the umbral oscillations have spatial and temporal characteristics indistinguishable from the quiet-sun oscillations, (3) a Fourier-Bessel analysis shows no obvious resonant frequencies which might represent natural oscillation modes of the sunspot umbrae, and (4) the centers of the umbrae have less RMS velocity than the edge of the umbrae. >From these analyses we conclude that the photospheric umbral oscillations are driven by an external source and that source is the global p-mode oscillations.

The Mees CCD imaging spectrograph

The Mees CCD (MCCD) instrument is an imaging spectroscopy device which uses the 25 cm coronagraph telescope and the 3.0 m Coude spectrograph at Mees Solar Observatory (MSO) on Haleakala, Maui. The instrument works with resolving power up to R ≈ 200 000 with significant throughput from λ3934 A (Caii K) to λ ≈ 10 000 A. A fast guiding active mirror stabilizes the image during observations. A rapidly writing magnetic tape storage system allows observations to be recorded at 256 kbytes s−1. Currently, the MCCD is used for imaging spectroscopy of solar flares at λ6563 A (Hα), and velocity measurements of umbral oscillations; future plans include emission line studies of active region coronae, and photospheric studies of solar oscillations.

A high capacity, high performance, small form factor magnetic tape storage system

A serpentine tape storage system using multichannel linear recording specifically addressing high-data-rate applications has been developed. It is a 5 1/4 in full-height form-factor drive including the controller, with a capacity of 2 GByte, which can be read or written in 11 min at a sustained data rate of 3 Mbyte/s. The system incorporates several significant technological advances, including a new read-while-write thin-film magnetoresistive read inductive write head, a new quarter-inch tape cartridge, and a heavily equalized data channel. A two-dimensional Reed-Solomon code is used to provide an error rate of <10/sup -14/. Write and read equalization are used to achieve excellent phase margins at 80 kb/in.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>