There's no reason to totally degrade the 64-bit capabilities of Athlon 64. A chip can still be AMD64-compatible even if it can't be connected to more than 4 GB of memory. The logical address space is still 48 bits (or whatver AMD64 says), while physically there's only enough address pins for 4G of memory.
Yeah, but so few desktops will use >4gb of RAM in the near future that this is almost useless as a market segmentation gimmick, because there wouldn't be any real performance hit. I suppose it would work if they only "degraded" the slowest-binning hammers, that way you would have a speed and memory limitation. Of course, they should still market them like a Duron64, not Athlon XP, in order to encourage consumption of ported software.
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