Informal generic term for sealed-enclosure magnetic-disk drives in which the read-write head planes over the disk surface on an air cushion. There is a legend that the name arose because the original 1973 engineering prototype for what later became the IBM 3340 featured two 30-megabyte volumes; 30--30 became ‘Winchester’ when somebody noticed the similarity to the common term for a famous Winchester rifle (in the latter, the first 30 referred to caliber and the second to the grain weight of the charge). (It is sometimes incorrectly claimed that Winchester was the laboratory in which the technology was developed.)