The P5Q / P45 chipset natively supports DDR2-1066, and up to DDR2-1200; 16GB (4 x 4GB). And w/ 2GB of RAM installed in one channel (Channel A), and 4GB installed in the other (Channel B), the 2GB from Channel A and the lower 2GB from Channel B will operate together in dual channel, while the remaining 2GB (upper) will operate in single channel.