MODULES MUST BE ORDERED AND INSTALLED IN PAIRS for Dual Channel mode. Kingston offers "K2" kit part numbers for Dual Channel mode.
If 4GB is installed, the recognized memory may be reduced to 3.5GB or less (depending on system configuration and memory allocation).
Per ASUS, this motherboard has a four rank limitation. Please see chart for proper upgrade path.
When four 667MHz modules are installed, the chipset will automatically reduce the speed to 533MHz.