How to check (on Windows) if CPU is 64-bit compatible?

I'm converting old Windows desktop machines from 2005-2009 into cheap Ubuntu Linux servers. I want to know which ones can handle a 64-bit OS and which can't. I read that some x86 CPUs are 64-bit compatible. The question is how to check.

Solution 1:

The definitive method:

1. Download CPUZ
2. Install and run it
3. Check the "Instructions" value for EM64T (if Intel) or AMD64 (if AMD).

Solution 2:

SecurAble

Run this utility and check the field "Maximum Bit Length"; it will show either 32 or 64. This utility is mainly used for checking if your CPU supports hardware virtualization, but it can be used for this purpose as well.