Desktop hard drive capacities will have quadrupled from today's 1TB to 4TB in four years, if the plans of Hitachi's storage arm - Hitachi Global Storage Technologies - come to fruition. As CNET News reports, the advance will result from the introduction of a new kind of drive head dubbed current perpendicular-to-the-plane giant magneto-resistive, or CPP-GMR for short. The first commercial drives with CPP-GMR head will likely come in 2009 or 2010.

The CPP-GMR drive essentially changes the structure of drive heads. Current drives come with a tunnel magnetoresistance head. In these, an insulating layer sits between two magnetic layers. Electrons can tunnel through the layer. Precisely controlling the tunneling ultimately results in the 1s and 0s of data. Unfortunately, drive heads need to be shrunk as areal density, the measure of the amount of data that can be squeezed onto a square inch of media, increases. Shrinking the heads increases electrical resistance, which in turn creates electrical noise and potential degradation in performance. Past 500 gigabits per square inch of areal density, TMR heads may not work reliably. (Current top-end drives exhibit an areal density of around 200 gigabits per square inch.)

In a CPP-GMR head, the insulator is eliminated and replaced by a conductor, usually copper. Instead of running parallel with the middle layer, the current runs at a perpendicular angle. The structure reduces resistance and thus allows the head to be shrunk. Put another way, current drive heads can read media where the tracks are 70 nanometers apart. The CPP-GMR heads will be capable of reading media where the tracks are 50 nanometers apart or smaller. Fifty nanometer tracks hit in 2009, and 30 nanometer tracks are expected to hit in 2011.