16-layers -- that's how many layers it takes to the hit the center of a 400GB Blu-ray disc, pops. That's 25GB per layer just like those dual-layer 50GB discs available for retail. Best of all, the technique used by Pioneer is expected to be backward compatible with existing Blu-ray gear since the specs and lenses required for pickup are identical. The prototype is read-only for the moment but R&D's on it so let's give them some time to work it out.Update
: Now that the English press release is out, it's less clear whether the new media -- whenever it might come to market -- will work in existing Blu-ray players or not. While "it is possible to maintain compatibility between the new 16-layer optical disc and the BD discs," players would seemingly require a modified optical pick-up mechanism to see the data. We'll learn more on July 13th when Pioneer discusses the breakthrough in detail.