@Mike, ram is around 1.6GB per second, you're beloved firewire maxes out 90 to 100MB per second (firewire 800) . .. 0.25 seconds to 5 seconds difference ?
You can't compare ram to harddisk, they're role in computing is different, ram keeps getting faster. Btw, the cache in the processor is even faster than ram, the one you see, 6mb cache etc. yes, that's the one, that's the first layer for cpu processing. second is ram.
Now if you notice, the new iMac has faster front side bus 1066Mhz, and also has 6mb cache, versus the old one 4mb cache. So the actual run runs faster, not to mention it runs cooler, since the ram requires less voltate (ddr3 vs ddr2)
and ofcourse the nvidia chip runs cooler too, since its integrated
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So to the thread starter, I'm not really sure if the dedicated graphcis card, the ati 2400 pro is way faster than the integrated 9400m. I haven't seen benchmarks yet. Thing is, currently, the new iMac can handle your needs. However, we don't know yet, if the graphics card will a crucial point in the future, no one really knows. However, your 9400M definitely will take advantage of OpenCL of the upcoming Snow Leopard.