Both are dual core - the "X2" in the name indicates dual cores. As mentioned earlier, both are Socket AM2 chips. The later Athlon 64 chips and the Phenom line indicated the number of cores by the designation "X--" after the name -e.g. Phenom X4 is a quad core, X2 is a dual core, etc. I actually had a Phenom X3, which was a tri-core. In reality, it was a quad core with one of the cores turned off. This is a common practice with chip makers - if a portion of a chip is defective, it can be turned off and sold as a lower priced model. The Athlon II models were actually Phenom chips with the L3 cache disabled. Intel does the same thing with the current Pentium and Celeron models - both are current Sandy Bridge and/or Ivy Bridge chips with various portions turned off.
I'm presently running a Athlon II X4 640 (Propus core). Too bad there isn't a way to enable that disabled L3 cache like you can a disabled fourth CPU core in an X3!