TDK has gone ahead and produced the 200GB Blu-ray Disc it announced a few weeks ago that it was working on. And while it appears to have failed to compress four standard dual-layer 50GB discs together into a single unit, it has nonetheless come up with a novel alternative.

According to a subscription-only report on Japanese-language site Techon, the 200GB BD contains six data-storage layers. Now, with a standard dual-layer BD offering 50GB of storage capacity, you might well assume that the 200GB model contains not six but eight data layers.

Providing the same capacity but with fewer layers means each layer must hold more data that a single-layer BD can. Indeed, TDK said it upped the capacity to 33GB - 32 per cent more than a standard BD data-carrying layer can. According to the report, it uses bismuth peroxide as the recording medium - heat it sufficiently with laser light and it forms bubbles of air. These reflect light differently than the surrounding material does, so can be used to record digital information in the way a CD or DVD's pits do.

That said, since the density of the bubbles is clearly different from that of a standard BD - hence the higher capacity - it's unclear whether a BD-compatible drive could actually read one of these things. And since the 200GB disc is not more part of the current Blu-ray Disc specification than this reporter is, you can argue that the 200GB disc, while technologically impressive, isn't about to allow anyone to cram the whole of the extended edition Lord of the Rings movies, extras and all, on a single, HD disc. ®