HotHardware.com posted a review on AMD's new DDR2 platform

In an effort to bolster system performance, Intel made the move to higher bandwidth DDR2 memory years ago but it wasn't enough to catch the Athlon 64 architecture. AMD didn't have the luxury (nor the need really) of supporting DDR2 memory however. The K8's integrated memory controller architecture, while offering significantly better latency characteristics, would have to be completely overhauled, which meant a significant core rip-up, if the Athlon 64 were to be able to interface to DDR2 memory. It would take more justification of the business case to invest in "surgically removing" (as AMD likes to call it) the A64's DDR memory controller and retro-fitting it with a DDR2 controller. This change would also require a ocket and CPU pin-out change as well, so backwards compatibility for existing motherboards was not option.

AMD Athlon 64 FX-62, Athlon 64 X2 5000+, Socket AM2, nForce 590 and RD580 AM2