Major Nelson has posted news that Microsoft are accepting U.S. registrations for an Xbox 360 System Update Preview program to help them prepare for an updated Xbox 360 disc format.
According to Digital Foundry, the new disc format adds an extra 1GB to Xbox 360 game discs:
"The maximum space allocated to game data on the current disc format is just 6.8GB out of a maximum of 7.95GB on a standard dual layer DVD, with over 1GB dedicated to a DVD-Video partition that also contained anti-piracy security sectors. Astonishingly, this meant that the last generation PlayStation 2 had a higher level of raw storage available to games developers than the newer Xbox 360. It seems that this video partition has either been drastically reduced or omitted completely in the new format Microsoft is looking to roll-out."