Does A780GM-A V1.1 support AMD Phenom™ II/Athlon™ II AM3 CPU like Athlon™ II x4 620?
Yes. This board can support AMD's AM3 processors. Please visit the following website for CPU support list of A780GM-A V1.1. Please refer to Product page - CPU tag
What CPU can be supported by this model? Is there any qualified list for reference?
This model can support Socket AM2 with AMD Athlon 64 FX/ Athlon 64/ Athlon 64 X2 Dual-Core/ Sempron processor. For qualified and validated CPU by ECS, please refer the CPU Support List as below super link.
I would like to upgrade memory from 1GB*2 to 2GB *2. Could you recommend what memory modules have better compatibility to this motherboard?
This motherboard supports DDR2 800/667/533, each DIMM slot supports up to 2GB. The following DDR2 memory modules have been tested and qualified for use with this motherboard.
