The company's giant magnetoresistive head will have a perpendicular current and means drive makers will be able to come out with 4TB drives by 2011

Hitachi Global Storage Technologies, the hard-drive arm of the Japanese conglomerate, has made what it says is the world's smallest read head for hard drives.

And, if it comes out in 2011 or so as expected, the head will allow Hitachi to continue to increase the density of drives, said John Best, Hitachi's chief technology officer. Current top-of-the-line desktop drives hold a terabyte.

With the new, elegantly named "current perpendicular-to-the-plane giant magnetoresistive" heads (CPP-GMR heads), drive makers will be able to come out with 4TB (terabyte) drives in 2011 and/or 1TB notebook drives.

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 500Gb per square inch of areal density, TMR heads may not work reliably. (Current top-end drives exhibit an areal density of around 200Gb 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 70nm (nanometres) apart. The CPP-GMR heads will be capable of reading media where the tracks are 50nm apart or less. Fifty nanometre tracks are expected to arrive in 2009, and 30nm tracks are expected to come in 2011.

Before TMR heads, the industry used more conventional GMR heads, but the current in the older versions ran parallel with the insulating layer.

"In a sense, [GMR] is making a comeback in a different form," said Best.

Earlier this month, France's Albert Fert and Germany's Peter Gruenberg won the Nobel Prize in Physics for their discoveries surrounding giant magnetoresistance in 1988.

The first commercial drives with a CPP-GMR head will probably come in 2009 or 2010.

Hitachi will present these achievements at the Perpendicular Magnetic Recording Conference next week in Tokyo.

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