Microsoft has been clear that the Windows 8 previews were a dead end.

"There is no upgrade path from Windows 8 Consumer Preview or Windows 8 Release Preview to the Released-to-Manufacturing (RTM) version of Windows 8," Microsoft said in an FAQ posted on the company's . "If you have already installed Windows 8 Consumer Preview or Windows 8 Release Preview, you will be required to perform a clean install. The installation process will automatically create a 'Windows.old' folder that contains all files from your Windows 8 Consumer Preview or Windows 8 Release Preview installation."

A "clean" upgrade is the least effective migration, since it does not retain applications, user accounts and settings, and moves data files -- Word documents and Excel spreadsheets, for example -- to a special folder.

A Windows 7-to-Windows 8 upgrade, on the other hand, preserves virtually everything, from programs and user accounts to Windows' settings and files stored in default locations.

Denny Cherry, a senior database administrator, independent IT consultant and as "Mrdenny," a blogger for the , recently posted instructions on how to fool Windows 8 RTM into upgrading the sneak peaks Microsoft offered users earlier this year.