Hot on the heels of Hitachi's 4TB-on-a-hard drive claim that will kick in by 2011, Western Digital has been doing some data-squeezing of its own. The company is talking of the "industry's highest demonstrated density" at 520 GB per square inch.

So, in other words, a single prototype exists which had its debut at - wait for it - the Perpendicular Magnetic Recording Conference in Tokyo this week, though there was an earlier demonstration in California.

3TB by 2010

So what does that amount of data density actually translate to? WD reckons that within a 3.5-inch hard drive storing 640 GB-per-platter single hard drives could reach 3TB and be "available in the 2010 timeframe".

So 3TB by 2010 and 4TB by 2011. Sounds reasonable to us. Perhaps we'll have worked out how to fill it by then, too.

The 4TB effect has been achieved with Western Digital's perpendicular magnetic recording (PMR) / tunneling magneto-resistive (TuMR) head technology, the company says. The tech was first demonstrated at WD's Magnetic Head Operation labs in Fremont earlier this month.

"The milestone was realised using our current-technology reader, illustrating the extendibility of PMR-TuMR head technology generations into the future" said Hossein Moghadam, chief technology officer at WD.

Current hard drives have a data density of around 200GB per square inch.