Re: Upgrade from XP 32-bit to Win 8 64-bit
It is simply not possible to upgrade from 32-bit to 64-bit. The changes between the two are substantial enough that nearly every system file and configuration would need to be replaced in ways that no installer could calculate. In essence, there are too many variables at work. While I know what you mean by upgrading Windows XP to Windows 8, as you would retain none of your settings, but still have working files on the drive, it really is a doozy. At this point, to initiate this type of "upgrade", you will really want to do a full install and not an upgrade. While this complicates things quite a bit, because you already have a valid copy of Windows XP, and just not the 64-bit version, and do not really want to retain your system settings from Windows XP (who would? who could?), you may even want to consider calling Microsoft to see if they can help you bypass the upgrade and let you do a one-time full install to get around this.
However, in general, it is widely known that an upgrade from a 32-bit operating system to 64-bit is impossible. Perhaps for licensing purposes, they have also made it impossible without thinking much about it. All the best, and please let us know your outcome.
Sincerely, Mike Fara Microsoft MVP Windows 8 Forums
Operating System Windows 8 Pro x64
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