AMD Phenom II X2 550 and Athlon II X2 250
 

Physically, Phenom II X2 core is a quad-core Phenom II die. Rejected quad-core dice are locked down to obtain processors with fewer cores and maximize yield. Athlon II, it turn, has the Regor die with two physical cores and no L3 cache. As a result, this die is only 117.5 mm², while Deneb takes up 258 mm². It will be interesting to see how the lack of L3 cache affects performance of the K10 core.

http://ixbtlabs.com/articles3/cpu/am...-2-250-p1.html