Well, here's a little chart to quickly summarize things: P-Pro additional Processor IA-32 MMX 3DNow! Enhanced 3DNow! ISSE instructions K6-2/K6-III X X X Athlon X X X X X "Spitfire" Athlon X X X X X PII X X X Celeron X X X PIII X X X X "Cumine" Celeron X X X X Sebastian Kaliszewski said: : I'd expand that with the one more tiny thing: P-Pro additional instructions : (like CMOV and likes) - everything above except K6-2/K6-III has it. So, as you can see, ALL support the basic IA-32 instruction set (what is used 99% of the time), and all support MMX. All AMD chips support the base 3DNow! (which was introduced with the K6-2), while the Athlon line of chips also support a few extra instructions in their "Enhanced" 3DNow! Intel's older processor cores (PII and Celeron) only support IA-32 and MMX, while the newer cores (PIIIs and the upcoming "Coppermine" Celerons) will also support ISSE. As for where these instructions sets stand in terms of applications, 3DNow! has the most applications, while ISSE is catching up. 3DNow! had the largest installed base of processors for quite some time, though I suspect that Intel has now caught up with their ISSE. None of these instructions sets (other then IA-32) really play a significant role in computers these days, they're all just used to speed up a few things here and there, and even then they don't usually improve performance by all that significant a margin. Anthony Hill hilla@uoguelph.ca