Is it this motherboard? http://www.motherboards.org/mobot/motherboards_d/MSI/915P%2BCombo%2B2%2B%2528MS-7140%2BV2.0%2529/ It supports 2GB (2*1 GB); the modules have to be the same type, i.e., either DDR or DDR2. Using both types at the same time will damage the motherboard. The chipset supports up to 1GB per slot.