The P4M800 PRO DRAM controller supports both DDR and DDR2 SDRAM. DDR adn DDR2 cannot be used concurrently. The maximum memory size can support up to 2 GB, 1GB per DIMM with double- sided DIMM. if install with 1GB single-sided DIMM, the system will recognize 512MB only due to each rank can address a maximum of 512MB. So if install with 2GB(1GB*2, single-sided DIMMs), the system will report 1GB(512MB*2 DIMMs) only.