Hello there,
This mobo has a ddr3 limit of 4gb because it has two slots for ddr3 rams, and ddr2 limit of 8gb because it has 4 slots for ddr2 rams, and for each slot regardless off ram type (ddr2 or ddr3), there is a limitation to the maximum memory the slot can handle and that is 2gb. So 4x(2gb ddr2)=8gb ddr2, or 2x(2gb ddr3)=4gb ddr3. And one last thing; you cannot have them both at the same time, you either have to go for ddr2 or ddr3.