In an effort to simplify the distribution of Windows Vista and make it easier for customers to upgrade, Microsoft will include the various retail versions of the operating system on one DVD instead of having separate discs for each Vista edition.
In the past, Microsoft distributed each version of the Windows client OS on its own disc. However, in a move it is calling "Windows Anytime Upgrade"--which cuts costs for Microsoft as well as making it easier for customers to upgrade--the version of Windows Vista that a customer buys will be activated by his or her product key and will be on a disk with the other editions of the OS.
More...Credit: PC World