No, they can't. The core is the same, but the CPUID instruction and the external interface are tweaked to prevent that configuration from working. To run in SMP, you will need an at least an Opteron 200 series processor. However, other than that tweak, the Opteron and Athlon64 are pretty much the same beast, which makes you correct. :) BTW, next year (around June according to the roadmap), AMD plans to launch the dual-core Opteron and Athlon64FX. Dual core Athlon64's (read: mainstream) are planned for around a year later. It will make for a nice upgrade path for existing Athlon64 systems. :)