Those users, however will have to do a "clean" installation of Windows 7, meaning that all data on the machine will be lost.

"Regarding XP, customers can purchase upgrade media and an upgrade license to move from Windows XP to Windows 7," a company spokeswoman said in an e-mail Tuesday morning. "However, they will need to do a clean installation of Windows 7."

In a follow-up reply to questions, the spokeswoman fleshed out what Microsoft means by upgrade. "The 'upgrade' part is referring to the license," she said. "You will be able to get the discounted 'upgrade' license, but it will include full bits."

That's how David Smith, an analyst with Gartner Inc., interpreted "upgrade" in Microsoft's description of what it would offer XP owners. "They're talking about the upgrade price," he said, pointing out that most software vendors use the term to designate a lower-priced version aimed at existing customers.

Although Microsoft Tuesday spelled the , it declined to provide pricing for them, or for the XP upgrade licenses.