Maximum recording density obtainable in particulate media

The recording density that has already been achieved with particulate media undoubtedly exceeds even the most optimistic expectations of most researchers in the field, who, long before the present state of development, had anticipated their replacement by thin metallic coatings or by some new and exotic formulation of novel particles. The old work horse not only survives but continues to lead the pack and even to demonstrate new spritness and vigor everytime it comes around the track! And if one judges by the recent IBM announcements, the old horse will continue to dominate the field well into the next decade. To be sure of course, he is not running unassisted, since the rules of the race permit a formidable array of electronic, electro-mechanical, and other props to be used, and they have been applied profusely and to great advantage. In this paper we do some crystal-ball gazing in trying to look at the future and to assess the attainable extensions in recording density using particulate media. Our analysis is primarily aimed in delineating the role of the magnetic parameters and the thickness of the coating and thus determining the way they would have to evolve in order to accomodate higher recording densities. The fundamental magnetic limits are several orders of magnitude beyond the present state of the art (4700 bits/cm, 235 tracks/cm). Therefore, it appears most likely that future advancements will be paced by other considerations-smaller particles with narrower range of shape and size distributions, uniform and well-aligned dispersions, thinner and smoother coatings, new types of transducers with better fringing field gradients and improved short wavelength and high frequency sensitivity, better track-following servos, more efficient codes, and a host of electronic signal processing, filtering, waveform shaping and compensation techniques. We conclude that these non-magnetic considerations will ultimately impose the upper bounds in recording density, which are estimated to be less than an order of magnitude beyond the present achievements (to about 10,000 bits/cm and 500 tracks/cm). The realization of this potential, however, is going to be increasingly more difficult, and it is not unlikely that we may have to switch horses along the way and to use thin metallic media, perpendicular recording, or some other not yet invented innovation.