On 08/23/11 7:40 PM, Always Learning wrote: > Surely it is more than mere memory addressing, a logic problem which has > existed since the original 8088 (and perhaps the 4040), it is extra > instructions and a re-write of some existing instructions ? the x86_64 architecture has teh same basic instructions as x86_32, but with more registers which are also wider 64 bit registers. there are new instructions on the newer CPUs, mostly for doing advanced multimedia numerical work like enhanced SSE instructions for MPEG. these new instructions can be used in 32 bit or 64 bit execution modes -- john r pierce N 37, W 122 santa cruz ca mid-left coast