Microsoft is planning to include the various retail versions of Vista on one DVD instead of having separate DVDs for each edition. As well as cutting costs for the company, it hopes that this will simplify the distribution of the operating system and make it easier for customers to upgrade.

The proposal, known as "Windows Anytime Upgrade," will mean that 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.

For example, customers who buy Windows Vista Home Premium from a retail store, will get a DVD that also includes Windows Vista Ultimate, but the product key for the purchase will only activate Home Premium and its features and functionality, said Mike Burk, a Microsoft spokesman.

"With Windows Anytime Upgrade, the idea is to provide customers with the most convenient user experience possible by enabling them to more easily and directly upgrade to a higher edition of Windows Vista from within their current edition," he said.

Consumers will have their choice of several versions of Windows Vista when it becomes available, which is scheduled for January 2007: Windows Vista Ultimate, which will cost US$399; Windows Vista Business, which will cost $299; Windows Vista Home Premium, which will cost $239; and Windows Vista Home Basic, which will cost $199.

Microsoft has said it plans to urge customers to purchase premium versions of Vista in favour of Windows Vista Home Basic, the entry-level version for US consumers.