# Flying height

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{{redirect|Head gap|the head gap on tape recorders|Tape head#Principles of operation}}
The '''flying height''' or '''floating height''' or '''head gap''' is the distance between the [disk read/write head](/source/disk_read%2Fwrite_head) on a [hard disk drive](/source/hard_disk_drive) and the [platter](/source/hard_disk_drive_platter).  The first commercial hard-disk drive, the [IBM 305 RAMAC](/source/IBM_305_RAMAC) (1956), used forced air to maintain a 0.002&nbsp;inch (51&nbsp;μm) <!-- I see spacing in a source here, UweIEEETonM.pdf (ref [3] in it), contradiciting with lower number for first hard drive, maybe they are excluding that one for some reason? Or might that info be wrong? --> 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](/source/air_bearing) slider," which generates its own cushion of pressurized air, allowing the slider and head to fly much closer, 0.00025&nbsp;inches (6.35&nbsp;μm) above the disk surface.<ref>{{cite web |url=http://www.almaden.ibm.com/timeline/Timeline_SJ_Research.pdf |title=Timeline of IBM San Jose Research Laboratory }}</ref>

In 2011, the flying height in modern drives was a few nanometers (about 5&nbsp;nm).<ref name=boettcher-et-al>{{cite journal |url=http://maeresearch.ucsd.edu/callafon/publications/2011/UweIEEETonM.pdf |first1=Uwe |last1=Boettcher |first2=Hui |last2=Li |first3=Raymond A. |last3=de Callafon |first4=Frank E. |last4=Talke |date=July 2011 |title=Dynamic Flying Height Adjustment in Hard Disk Drives Through Feedforward Control |journal=[IEEE Transactions on Magnetics](/source/IEEE_Transactions_on_Magnetics) |volume=47 |issue=7 |pages=1823–1829 |doi=10.1109/TMAG.2011.2136328 |bibcode=2011ITM....47.1823B |s2cid=30300684 }}</ref><ref>{{Cite journal|last1=Yu|first1=C.|last2=Luo|first2=Y.|last3=Li|first3=H.|last4=Wen|first4=J.|last5=Qian|first5=Z.|last6=Zhou|first6=T.|date=January 2020 <!-- rather go with Date of Publication: 18 December 2019?-->|title=Stability of Spin Torque Oscillators for MAMR: Perspectives of Materials and Design|journal=IEEE Transactions on Magnetics|volume=56|issue=1|pages=1–5|doi=10.1109/TMAG.2019.2951424|bibcode=2020ITM....5651424Y|s2cid=209459752|issn=1941-0069}}</ref> 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](/source/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.<ref name=pcguide>{{cite web |url=http://www.pcguide.com/ref/hdd/op/heads/op_Height.htm |title=Hard Disk Read/Write Head Operation |author=Charles M. Kozierok |work=The PC Guide }}</ref> 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.<ref>{{cite journal |first1=Junguo |last1=Xu |first2=Yuki |last2=Shimizu |first3=Lizhi |last3=Su |date=27 November 2006 |title=Drive level measurement of flying height modulation and control of slider disk contact |journal=Tribology Letters |volume=24 |issue=2 |pages=159–162 |doi=10.1007/s11249-006-9153-1 |s2cid=136760795 }}</ref>

However, [hermetically sealed](/source/hermetic_seal) enclosures are beginning to be adopted for hard drives filled with [helium](/source/helium) gas, with the first products launched in December 2015,<ref name=wd-helium>{{cite news |url=http://www.computerworld.com/article/3011142/data-storage/wd-ships-worlds-first-10tb-helium-filled-hard-drive.html |first=Lucas |last=Mearian |date=2 December 2015 |title=WD ships world's first 10TB helium-filled hard drive |work=Computerworld |archive-date=26 January 2016 |access-date=3 March 2016 |archive-url=https://web.archive.org/web/20160126073353/http://www.computerworld.com/article/3011142/data-storage/wd-ships-worlds-first-10tb-helium-filled-hard-drive.html |url-status=dead }}</ref> starting with capacities of 10 TB.<ref name=wd-helium /><ref>{{cite news |url=http://www.digitaltrends.com/computing/seagate-helium-filled-hard-drive/ |author=Gabe Carey |date=14 January 2016 |title=Seagate is finally joining HGST in its helium-filled hard drive efforts |work=Digital Trends }}</ref>

==See also==
* [Head crash](/source/Head_crash)

==References==
{{reflist}}

Category:Hard disk drives

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Adapted from the Wikipedia article [Flying height](https://en.wikipedia.org/wiki/Flying_height) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Flying_height?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.