I want change my 32-bit Athlon with a 64-bit Phenom. Do I need to change my OS (32-bit Windows 7) as well?
closed as not a real question by Joey, Chris W. Rea, Karan, MaQleod, Indrek Oct 28 '12 at 6:55
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No. A phenom is able to execute both 32 bit and 64 bit mode.
Slightly longer answer:
You can run a 32 bit installation of windows 7 on both 32 bit only CPUs and on CPUs which can do both 64 and 32 bit mode. In the last case the CPU will simply behave as an older 32 bit CPU.