DISK WEAR LEVELING
Wear Leveling is a feature incorporated by some disk manufacturers to minimize wear on disk recording surfaces from accidental contact with the read/write heads. The technique was used by Western Digital and perhaps by others for drives that achieved improved data density by mounting the heads on an extension that put the heads closer to the disk surface than the rest of the read/write assembly. Wear Leveling moves the disk heads from time to time (every 15 seconds) when they are not in use so that any random grazing contacts between the heads and the recording surfaces are distributed over the disk and are not concentrated in specific areas.
In the early to mid 1990s, disk read heads included a protrusion that flew very close to the drive surface -- reducing the altitude from the 150 Angstrom range to perhaps 50 Angstroms. The protrusion was removed when thin film heads came into use. Wear Leveling may be less relevant to later drives.
It is not known whether wear leveling actually serves any useful purpose in modern drives. The only demonstrable effect is that it causes clicking noises from the "inactive" drive that some people find to be disconcerting.
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Copyright 1994-2002 by Donald Kenney.