Disk storage technology strives to improve areal density - in other words, how much data can be packed into a given space. And where MR technology can store up to 3.3 gigabytes per square inch, GMR squeezes in 10 gigabytes per square inch - over 40 gigabytes per drive.
As more data is squeezed into the same amount of space, the devices needed to accurately read the data also must keep pace. GMR is designed to pack as much data onto a disk that can be retrieved accurately - with as few moving parts as possible.
The technology is based on a discovery made by two scientists in the late 1980s. The two -- Peter Gruenberg of Julich, Germany and Albert Fert of Paris -- figured out that materials made up of very thin, alternating layers of various metallic and nonmetallic elements experienced significant variations in resistance.
Disk drives that are based on GMR use these properties to help control a sensor that responds to very small rotating on the disk. The magnetic rotation yields a very large change in sensor resistance, which in turn provides a signal that can be picked up by the electric circuits in the drive.