The first commercial hard-disk drive, the IBM 305 RAMAC (1956), used forced air to maintain a 0.002 inch (51 μm) between the head and disk.
The IBM 1301, introduced in 1961, was the first disk drive in which the head was attached to a "hydrodynamic air bearing slider," which generates its own cushion of pressurized air, allowing the slider and head to fly much closer, 0.00025 inches (6.35 μm) above the disk surface.
[2][3] Thus, the head can collide with even an obstruction as thin as a fingerprint or a particle of smoke.
[4] Because disk drives depend on the head floating on a cushion of air, they are not designed to operate in a vacuum.
[5] However, hermetically sealed enclosures are beginning to be adopted for hard drives filled with helium gas, with the first products launched in December 2015,[6] starting with capacities of 10 TB.