In 1973, the IBM 3340 disk unit
introduced to the industry an advanced disk technology
known as "Winchester," after IBM's internal
project name. The 3340 featured (1) a smaller, lighter
read/write head and (2) a ski-like head design that
enabled the head to ride closer to the disk surface
-- on an air film 18 millionths of an inch thick.
The 3340 doubled the information density of IBM
disks -- to nearly 1.7 million bits per square inch.