Winchester discs

Mass data storage represents something of a problem. Floppy discs are probably inadvisable under the severe conditions at sea (vibration, large motion, dirty air, etc.). Some forms of data storage that do appear desirable are Winchester discs (if head crashes can be avoided), digital tape recorders, electronic memory systems (protected from power interruptions), or bubble memories (a bubble memory for the Apple II has become available commercially). 

Winchester discs are molded as blanks in engineering plastics, usually General Electric s Ultem polyetherimide, then coated with an epoxy-ferric oxide layer. The main requirement in manufacturing these discs is absolute flatness because the magnetic read/write head moves only 8-20 microinches above the disc surface and is spinning at a high speed of 3,600 rpm. Any microscopic bump can thus cause damage to both the disc and head. 

The third type of medium, the rigid disc, makes less use of plastics, the disc substrate being polished aluminium. Rigid discs were introduced in a 14 in diameter version contained in a plastic cartridge, but the trend has been for miniaturisation and a number of Winchester disc devices are now in use. The plastic used for the cartridges is typically polycarbonate. 

The stretched disc, developed by 3M Company as an alternative to the Winchester disc, is said to combine the performance characteristics of hard discs with the economy and environmental tolerance of a floppy disc. The discs are 5 4 in. in diameter and are able to store 12-Megabytes of computer data with storage capacity up to 100-Megabytes is thought possible. Unlike Winchester discs, stretched discs consist of a magnetically coated polyester film stretched over an injection-molded disc. The film is bonded to the raised edges of the disc, thus producing a compliant surface with a 250 pm gap between the film and... 

Hard-disc drive heads are subjected to a heavier use and therefore need a different design in order to prevent wear and extend the useful life of both the disc and the head. Hard-disc drive heads (also known as Winchester heads) make no physical contact with the hard disc. They are designed to fly very close to the disc, supported by the air flow resulting from the disc rotation. Fig. 5.18. The magnetic element in Winchester heads is usually a Mn-Zn ferrite. 

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