Microsoft has confirmed that all versions of Vista will be shipped on a single DVD, in a feature called Windows Anytime Upgrade.
According to a spokesperson for the company, "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".
Users would only be installing the version of the operating system that they had purchased, as the product key would be version-specific. Versions range from Starter to Ultimate editions.
Asked if this system meant upgrades would be cheaper, as production and retail costs for Microsoft will be lowered, the spokesperson said they could not give any details of pricing at the moment.
The spokesperson also denied that Windows Anytime Upgrade would prove an attractive target for hackers, saying Vista was "the most secure version of Windows yet".