Western Digital has claimed to have created the world's highest density hard drive platter, a unit that packs in 520Gb per inch squared - more than double the highest density products on the market today.

They typically offer an data density of 200Gbpi² - just not enough to yield the 640GB-per-platter storage capacity needed to yield 3.5in hard drive capacities of 3TB, WD said.

Interestingly, WD said it had demonstrated the higher areal density using a Tunneling Magneto-Resistive (TMR) read/write head of the kind Hitachi this week said wouldn't be up to the tasks of reading data off a 500Gbpi² platter. Hitachi made that claim when it announced its putative successor head technology, Current Perpendicular-to-the-Plane Giant Magneto-Resistive (CPP-GMR).

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For its part, WD said its latest development showed "the extendibility of TMR head technology generations into the future".

WD said it expects 3TB drives to go on sale in 2010, but curiously it based that forecast on "on the industry's current density growth rate of more than 40 per cent per year" rather than when it expects to be able to bring its 520Gbpi² platters to market. Will the two coincide? Only a few years to wait to find out...

In January this year, Fujitsu said it had developed the technique that will allow it to create drives with an areal density of 1Tbpi². It too reckons it will be able to offer HDDs of that density in 2010.