I would recommend against installing Windows 7, because it is not supported by Microsoft anymore..
Windows 7 is supported by security updates until January 14, 2020 in extended support. Mainstream ended a couple years ago, which is why there should have been no new features--and yet we got GWX and telemetry + WindowsUpdate bundles in an attempt to make it as bad as 10 so you'd have no reason not to update.
It's the socket 939 and 754 A64s that had no CMPXCHG16b so could only run 32-bit Win8.1 and 10. Even they could run 64-bit Win 7 or 8, although they could only hold 4GB and 2GB of RAM, respectively.