Just don't get confused by the two different types of 64 bit processors. As long as you are talking about AMD64, or x86-64 - pretty must all of the distros support it. This is what most people mean when they say 64 bit. Pretty much every common processor supports the AMD64 extensions these days. There is, however, another 64 bit architecture - the Intel Itanium chips - not nearly as many distros support that - I see that redhat / fedora does http://fedoraproject.org/wiki/Architectures/IA64 Those processors are typically much more expensive, however.