For nearly 50 years, the disk drive industry has focused nearly exclusively on a method called longitudinal magnetic recording, in which the magnetisation of each data bit is aligned horizontally in relation to the drive's spinning platter. In longitudinal recording, the fields between two adjacent bits with opposing magnetisations are separated by a transition region.
While areal densities have historically pretty much doubled every year,more recently however, the rate of increase has slowed, and the limit of areal densities for hard disk technology using longitudinal recording - due to the superparamagnetic effect - is now generally reckoned to be in the region of 100 to 200 Gbits/in2.
This has led to more aggressive approaches to delaying the superparamagnetic effect being sought, and the emergence of perpendicular magnetic recording (PMR) technology as a solution capable of doubling hard disk data densities in the relative short term and of ultimately enabling a more 10-fold increase in storage capacity over today's technology.
