Flying height

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The flying height or floating height or head gap is the distance between the disk read/write head on a hard disk drive and the platter. The first commercial hard-disk drive, the IBM 305 RAMAC, used forced air to maintain a 0.002 inch (51 μm) spacing 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.[1]

In 2011, the flying height in modern drives was a few nanometers.[2] Thus, the head can collide with even an obstruction as thin as a fingerprint or a particle of smoke. Despite the dangers of hard drive failure from such foreign objects, hard drives generally allow for ventilation (albeit through a filter) so that the air pressure within the drive can equalize with the air pressure outside.[3] Because disk drives depend on the head floating on a cushion of air, they are not designed to operate in a vacuum. Regulation of flying height will become even more important in future high-capacity drives.[4]

However, hermetically sealed enclosures are beginning to be adopted for hard drives filled with helium gas, with the first products launched in December 2015,[5] starting with capacities of 10 TB.[5][6]

See also[edit]


  1. ^ "Timeline of IBM San Jose Research Laboratory" (PDF).
  2. ^ Boettcher, Uwe; Li, Hui; de Callafon, Raymond A.; Talke, Frank E. (July 2011). "Dynamic Flying Height Adjustment in Hard Disk Drives Through Feedforward Control" (PDF). IEEE Transactions on Magnetics. 47 (7): 1823–1829.
  3. ^ Charles M. Kozierok. "Hard Disk Read/Write Head Operation". The PC Guide.
  4. ^ Xu, Junguo; Shimizu, Yuki; Su, Lizhi (27 November 2006). "Drive level measurement of flying height modulation and control of slider disk contact". Tribology Letters. 24 (2): 159–162. doi:10.1007/s11249-006-9153-1.
  5. ^ a b Mearian, =Lucas (2 December 2015). "WD ships world's first 10TB helium-filled hard drive". Computerworld.
  6. ^ Gabe Carey (14 January 2016). "Seagate is finally joining HGST in its helium-filled hard drive efforts". Digital Trends.