Microsoft has said that some in-place upgrades from Windows Vista to the new Windows 7 may take some users over 20 hours to complete.

Chris Hernandez, who works in the Windows deployment team Said that the best that users can hope for is a 1 hour and 24 minute process. So-called clean installs, where the user overwrites an existing edition of Windows to end up with the OS, but no former data or applications, take less time: from 27 to 46 minutes.

One of the main goals with Windows 7 in general has been to be better than Vista. As part of the Windows Upgrade team we have tracked Windows 7 upgrade performance using Vista as our baseline comparison. The in-place upgrade from Vista Service Pack 1 (SP1) to Windows 7 at least 5% faster than an in-place upgrade from Vista SP1 to a new copy of Vista SP1.

Windows 7 upgrade time is faster or equal within a 5% threshold to the Vista SP1 upgrade time.

Hernandez said the in-place upgrade times were obtained from lab machines in three different configurations: labeled low, mid-range and high-end — with three simulated users: a medium user, a heavy user and a super user. The profiles differed in the amount of data and the number of applications that were on the PC before the upgrade to Windows 7. The medium user profile, for example, assumed 70GB of data and 20 applications; the super user profile, on the other hand, contained 650GB of data and 40 applications. Microsoft’s data showed that so-called edium” users, those with 70GB of data and 20 applications would spend between 1 hour and 40 minutes and 2 hours 50 minutes doing a 32-bit upgrade. The more powerful the PC, the faster the upgrade, according to Microsoft. Heavy users: which Microsoft posed as people with 125GB of data and 40 applications, would need between 2 hours and 40 minutes and 5 hours and 43 minutes to do the same upgrade.