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

The best that users can hope for is a 1 hour and 24 minute process, said Chris Hernandez, who works in the Windows deployment team, in a company blog published Friday.

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.

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.

"One of the main goals with Windows 7 in general has been to be better than Vista," explained Hernandez on the blog. "As part of the Windows Upgrade team we have tracked Windows 7 upgrade performance using Vista as our baseline comparison."

Microsoft's goal, he added, was to make an 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.

Hernandez claimed Microsoft's testing showed, "that Windows 7 upgrade time is faster or equal within a 5% threshold to the Vista SP1 upgrade time." A table published in his blog post showed that in every situation, a Windows 7 upgrade was more than 5% faster than one using Vista.

But the data also illustrated that many of the in-place upgrade scenarios took an extremely long time. Of the 16 scenarios -- three each for medium and heavy profiles, two for the super profile, with the tests run for both the 32- and 64-bit versions of Windows 7 -- only four clocked in at less than two hours, and only eight in under three hours.

The speed record, according to Microsoft's testing, was the medium user profile upgrading to Windows 7 64-bit on a high-end PC, at just under 84 minutes.

But most of the in-place upgrades couldn't come close to that mark. The slowest 32-bit upgrade, for instance, was a super user on a medium machine -- Microsoft didn't bother testing that profile on a low-end system -- that crossed the tape at an amazing 20 hours and 15 minutes. The longest 64-bit upgrade was 10 hours, 8 minutes.