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I need to reinstall Windows on a laptop. I have the product key (its on the laptop), and I know it is Windows 7 Home Premium.

I need a way to determine if 64-bit or 32-bit Windows is installed, so that I can download the correct one from Microsoft. The computer is messed up so I do not have access to Windows to check it with systeminfo.

I took out the hard drive and hooked it to another computer, but when I run systeminfo it just gives information for the host computer, I did not see a way to change this.

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You do understand the product key for Windows 7 Home Premium can be be used to install 32-bit or 64-bit installation. If the HDD is attached to another computer then you can view the contents of the HDD and determine what you had installed per Fran's answer. – Ramhound Jul 2 '12 at 15:24
up vote 30 down vote accepted

If you see a folder in the root of that drive named Program Files (x86) then it has 64-bit Windows installed.

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A slightly more accurate way of detecting 64-bit windows is to look for folder %SystemRoot%\SysWOW64 (commonly Windows\SysWOW64) since it contains the binaries windows uses to launch 32-bit applications it should not be present on 32-bit windows installations. This is a little more accurate than checking for Program Files (x86) because I recall seeing an installation option somewhere in Windows Vista which allows that folder to be renamed, but I've never seen one for SysWOW64.

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-1: It's not officially possible to relocate Program Files or Program Files (x86) via an unattended setup anymore. It was possible with XP. Obligatory Old New Thing Reference – afrazier Jul 2 '12 at 21:01
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"not officially possible" does that mean "unofficially it's still possible"? – Bob Davies Jul 2 '12 at 21:03
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It's not possible with the WAIK. I wouldn't be surprised if someone's come up with a nasty hack that appears to work though. N.B.: I'm not talking about people simply junctioning the folder to another drive, which is also unsupported, but actually renaming Program Files. – afrazier Jul 2 '12 at 21:07
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Good to know thanks. Though I think I'll stick with my option since in my experience it's slightly less fallible than the alternatives. – Bob Davies Jul 2 '12 at 21:09
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Why exactly was this voted up so many times? The user was running Windows 7 Home Premium. There is NO WAY he doesn't have Program Files (x86) if a 64-bit version was installed. – Ramhound Jul 5 '12 at 15:19

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