GMR head
A read head built on giant magnetoresistance — the 1988 discovery that let disk capacity explode through the late 1990s and 2000s.
Giant magnetoresistance (GMR), found independently by Albert Fert and Peter Grünberg in 1988 and awarded the 2007 Nobel Prize, is a large change in a multilayer's electrical resistance when a weak magnetic field flips the relative magnetisation of two ferromagnetic layers. IBM turned it into a spin-valve read sensor and shipped the first GMR drive in 1997. Far more sensitive than the earlier anisotropic (AMR) head, it could read the tiny fields of much smaller bits and sustained the era's 40–100% annual density growth. It was later succeeded by even more sensitive tunnelling-magnetoresistance (TMR) heads.