Actually, a Dual Core processor is, if designed correctly, inherintly more efficient than Dual CPUs. Dual CPUs have to communicate with each other on a bus (even though the PMs is very fast), as well as with the memory (even if the bus is seperate, this tends to be quite slow, even on speed king AMD - in comparison to core speed).
Dual Core CPUs, which should have seperate caches (both Intel and AMD do) have by definition the most efficient way to communicate with each other. As long as they can address the bus seperately they have the POTENTIAL to be better than a same-speed Dual Processor.
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