Twenty-layer optical disks that can hold half a terabyte of data could be with us within a few years, according to Sony researchers working on holographic recording techniques.

The technology is likely to produce standard-sized 12cm disks with room for 500GB of anything from high-definition video to computer data by 2010. Sony bases the claim on its most recent research using the 'Micro-Reflector' method to write to seven layers per disk.

Fringe in the middle, not on top

Such holographic techniques take many forms and have been in development at various companies for several years now. Sony's version relies on shining light on both sides of the disk simultaneously. This creates interference patterns in the layer being written to, with each pattern - or fringe - capable of representing a single bit of data.

Because the success of new method is predicated on ramping up the number of layers per disk, Sony prefers to emphasise the multilayer aspect, rather than the holographic element.

Whatever they like to call it, we'll just take their word for it that it works and wait for the day when we can back up an entire hard drive on one DVD-sized disk.