Back in January, Toshiba unveiled a triple layer HD DVD, which features a capacity of 51GB.  While three 15GB layers would have only added up to 45GB in total, Toshiba managed to get an extra 2GB on each layer to achieve the 51GB total capacity.  In April, Toshiba submitted this triple layer format to the DVD Forum and then in September, there were reports about the DVD Forum approving revision 1.0 of the 51GB format. 

Now, going by this X-bit labs report, the DVD Forum has officially approved version 2.0 of the triple-layer HD DVD disc format.  The approval of the HD DVD-ROM 51GB part 1 physical specifications, version 2.0, took place during the 40th Steering Committee meeting on November 15th, 2007, which means that manufacturers can start producing these discs with the availability of these physical specifications.  It also means that HD DVD media will come in a capacity choice of 15GB, 30GB and 51GB, allowing it to compete with Blu-ray's maximum 50GB capacity advantage it has had up until now.

While there are talks about PC HD DVD drives and standalone HD DVD players being physically capable of reading the triple layer format, so far neither Toshiba nor the DVD Forum have confirmed compatibility with existing HD DVD devices.  However, if it turns out that new HD DVD writers would be required to write to the triple layer HD DVD format, there are only a small number of HD DVD writers that have been sold so far, which means that it is possible to release new triple layer writers before these start shipping with most new PCs as standard, assuming this happens over time. 

If all existing HD DVD players can read the triple format disc, even if it just takes a firmware update, it would mean that Blu-ray will no longer have the competitive advantage of 50GB per disc for video titles, as this would mean that studios would be able to make use of the extra HD DVD capacity also. 

Thanks to Lenco for letting us know about this news.  Further info can be read in this source X-bit labs report.