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read/write head

read/write head A component of a disk drive that records and retrieves data from magnetic disks. Read/write heads are also used sometimes to record and retrieve data from magnetic tapes. In the case of disk drives the assembly consists of a head, sometimes known as a slider, and a mounting arm, known as a flexure. There are two categories of head: those used in floppy drives in which the slider is in contact with the media, and those used in “rigid drives” in which the head flies above the surface of the media. The flying height of the latter depends upon the slider geometry, the flexure loading force, and the rotational speed of the disk.

Early drives (e.g. the IBM 3330–11) employed a flexure with a high load force, typically 350 grams, and the heads were withdrawn from the disk surface before rotation stopped. The 3340 Winchester drive first delivered by IBM in 1973 employed a radically new head design. Heads of this type are now known as Winchester heads, and have the following characteristics:

the read/write head is supported by a trimaran structure, with two outriggers supporting a narrow inner “hull”, i.e. the slider;

before drive operation, and when it ceases, the heads rest on the disk surface, which is lubricated;

the loading force was reduced to 10 grams;

the flying height was reduced to 0.25 micrometers (10 microinches) compared to 0.8 μm in the 3330.

With the introduction of the IBM 3370 (Whitney drive) in 1979 the head design was again changed. The size of the slider was made smaller and was fabricated using “thin film” technology; also the flexure was made much simpler. The result of this was a much more stable head that can be loaded, although not in the 3370, toward the media while it is rotating. Winchester heads cannot be so loaded. The term Whitney is now used to describe the type of head and flexure outlined above even if it is not manufactured by thin film techniques, in which case it is sometimes called a minicomposite head.

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