Many advances in flexible disk technology result from close cooperation between disk developer and the drive developers. While not ignoring progress in drives, this paper will emphasize the technological developments in disks. These developments are aimed at increasing the data capacity, the reliability, the durability and the range of operating temperatures and reducing manufacturing cost. The topics covered include developments in particulate and thin film coatings, the magnetic and non-magnetic properties of disks, the relative merits of longitudinal and perpendicular recording. Important trends are: a storage density (in bits/in2) which increases by a factor of ten every eight years, a widening in the range of operating temperatures and a greatly increased sensitivity to the protection of the disk and its durability. The paper concludes with a discussion of current problems, their possible limiting effect on progress and the possible future relationship of removable magnetic disks (flexible, Bernoulli, "stretched-surface" and rigid) reversible optical disks, and semi-conductor memories.
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