It wasn't even close.
After reading the round-by-round account of our dual-core desktop CPU prizefight, it should come as no shock that AMD's Athlon 64 X2 chips are the runaway victors here, laying out the Intel Pentium D and Pentium Extreme Edition 840 chips pins up. If we had to call out one chip, AMD's Athlon 64 X2 4400+ is an outstanding bargain given the competition, but as our results show, any AMD dual-core CPU will serve you better than its similarly priced Intel equivalent.
If you're wondering why there's such a striking performance difference between the two companies' processors, it likely has something to do with the memory controller. Among the technological differences between the two, AMD's memory controller--the component that sends information back and forth between your system's CPU and the memory--is an integrated part of the Athlon 64 X2's chip architecture. Intel's memory controller, however, exists as a separate piece of silicon on the motherboard. The additional distance between the CPU and the memory controller adds to the processing lag time and likely plays a part in Intel's lower scores.
Whatever Intel's strategy, it doesn't seem to have held up. We're very interested to see what happens when the next generation of chips and chipsets hits the market starting in January. But until then, AMD's Athlon 64 X2 should be your dual-core processor of choice.
