Floppy Disk Storage (history)

> Recently, however, the floppy disc industry has started to use both sides of the floppy disc for data transfer operations, the purpose primarily being to increase capacity. Thus only a single relatively low speed accessing mechanism continues to be employed, and the transducers on opposite sides of the element are in a generally opposed relation, with only a slight offset in the head gaps to avoid flux interaction. Because it is thought necessary to account for perturbations in movement of the flexible disc from its principal plane, recording heads and mounts are utilized that are essentially derived from the flying head technology. Specifically, *** a pair of small, identical slider heads are used, each mounted adjacent the end of a long resilient cantilevered head support *** , and mechanically urged together with a total force of approximately 8 grams. The concept is that as the flexible disc deviates from its principal plane, both of the heads tend to follow the actual position of the disc passing between them and permit contact recording without excessive wear or signal degradation. Accepted industry standards for functional specifications are 1,000,000 revolutions without substantial degradation in reproduced signal amplitude, and 3,000,000 revolutions without significant head wear.

> There are, however, *** significant problems and limitations arising from the use of this double, symmetrical and very compliant head mechanism *** . The resilient mounts are relatively complex and must be precisely manufactured, and therefore are costly to manufacture and maintain. Furthermore, they require redesign, by each floppy disc manufacturer, of the carriage, head support mechanisms and associated structure, becase they have volumetric configurations incompatible with current structures. In addition, the head loading force and the mechanical configuration require that special provision be made to insure that the head does not constantly land at the same point and thereby cause undue wear. In addition, the long flexible columns used in the existing type of structure tend to bend in a slight S shape or shift differentially in response to perturbations in the disc surface position. This introduces both a degree of offset relative to the track center, reducing reproduced signal amplitude and tending to limit the positional accuracy which can be obtained, which in turn limits the track density which can be achieved. [...]

> SUMMARY OF THE INVENTION: A device for effecting data recording and reproduction operations with each of the two sides of a pliant, non-rigid magnetic record element employs *** a fixed transducer on one side and a resilient element supporting a movable transducer on the other *** . An asymmetrical system is thus provided in which the record element is deflected by the fixed transducer but confined against the fixed transducer, despite perturbations in its movement, by the movable transducer. The movable transducer may be a smaller slider transducer that is mounted via a short length gimbal adjacent the end of a spring-loaded pivotable support arm. The arm mechanism urges the slider transducer and the intervening record element against the surface of the fixed transducer with a light force, although the fixed transducer is positioned to penetrate slightly into the nominal plane of the record element. The configuration of *** the spring-loaded arm mounting the slider transducer is compatible with the configuration of the mechanism ordinarily supporting a pressure pad, so that the structure is thus directly substitutable in the space avilable in the prior single sided system *** . The spring-loaded support arm has a high damping coefficient and effectively holds the flexible magnetic recording element against the fixed transducer, at a precise radial position, as well as correcting deflections of the record element, although wear is less than in existing double sided systems.

U.S. Patent 4,151,573, Apr. 24, 1979 https://patents.google.com/patent/US4151573