My brother has a 64-bit capable system running 32-bit Windows 7. I have the 64-bit upgrade disk from upgrading my own system. If I use it to upgrade his system as well, will he still be able to register using his 32-bit Windows 7 product key?
It depends on whether it's an Retail or an OEM/System Builder licence.
Retail Product Keys work for both, 32bit and 64bit
OEM/System Builder Keys work for only the licensed one, 32bit or 64bit.
Also your upgrade DVD must be of the same edition as his key!
For example if your upgrade disk is for Windows 7 Ultimate but his key is for the Home Premium edition the key won't work.
If its a new copy of windows never installed, Yes, it is valid for either 32 or 64 bit, its up to you which architecture you want to use. Please note 1 key, 1 license. You can't install 32 bit one computer and install 64 bit on another computer using the same key.
The retail packages of Windows 7 come with both 64-bit and 32-bit installation disks with the same product key
if you already have 32bits installed and you want to upgrade to 64bits then the key will not work.
A fantastically thorough explanation, thanks!
The key will not work because you can only upgrade to the same architecture (i.e 32 bit to 32 bit).