Editing Disk read-and-write head (section)

== Inductive heads ==
Inductive heads use the same element for both reading and writing.

=== Traditional head ===
The heads themselves started out similar to the heads in [[tape recorder]]s—simple devices made out of a tiny C-shaped piece of highly magnetizable material such as [[permalloy]] or [[ferrite (magnet)|ferrite]] wrapped in a fine wire coil.  When writing, the coil is energized, a strong [[magnetic field]] forms in the gap of the C, and the recording surface adjacent to the gap is magnetized.  When reading, the magnetized material rotates past the heads, the [[magnetic core|ferrite core]] concentrates the field, and a [[current (electricity)|current]] is generated in the coil. In the gap the field is very strong and quite narrow.  That gap is roughly equal to the thickness of the magnetic media on the recording surface.  The gap determines the minimum size of a recorded area on the disk.  Ferrite heads are large, and write fairly large features.  They must also be flown fairly far from the surface thus requiring stronger fields and larger heads.<ref name=":0">{{Cite web|url=https://www.tomshardware.com/reviews/hard-drive-magnetic-storage-hdd,3005-2.html|title=Read/Write Head Designs: Ferrite, Metal-In-Gap, And Thin-Film - Hard Drives 101: Magnetic Storage|date=2011-08-30|website=Tom's Hardware|language=en|access-date=2019-04-13}}</ref>

=== Metal-in-gap (MIG) heads===
Metal-in-gap (''MIG'') heads are [[Ferrite (magnet)|ferrite]] heads with a small piece of [[metal]] in the head gap that concentrates the field.  This allows smaller features to be read and written.  MIG heads were replaced by thin-film heads.

===Thin-film heads===
First introduced in 1979 on the [[IBM 3370]] disk drive, [[thin film|thin-film technology]] uses photolithographic techniques similar to those used on semiconductor devices to fabricate hard drive heads.  At the time, these heads had smaller size and greater precision than the ferrite-based heads then in use; they were electronically similar to them and used the same physics. Thin layers of magnetic (Ni–Fe), insulating, and copper coil wiring materials were built on ceramic substrates that were then physically separated into individual read/write heads integrated with their air bearing, significantly reducing the manufacturing cost per unit.<ref>{{cite web  |url=https://www.computerhistory.org/storageengine/thin-film-heads-introduced-for-large-disks/ |title=1979: Thin-film heads introduced for large disks  |date=December 2, 2015 |website=Computer History Museum |access-date= June 19, 2019}}</ref> Thin-film heads were much smaller than MIG heads and therefore allowed smaller recorded features to be used. Thin-film heads allowed 3.5&nbsp;inch drives to reach 4&nbsp;GB storage capacities in 1995. The [[geometry]] of the head gap was a compromise between what worked best for reading and what worked best for writing.<ref name=":0" />