x64, also known as x86_64, has been around in consumer-level computers for a little over 5 years, having been introduced to the public by AMD in their famous K8 lineup back in 2003. The x86-64 instruction set, which AMD had presented in 2000, had for a goal to extend the existing x86 achitecture in order to be able to address more physical and virtual memory, use newer SSE instructions sets, and eliminate some of the older, archaic 16 bit instructions. 64 bit would also bring many more advantages...