> configurations. The x86_64 vs. i386 difference is odd; maybe they treat > the memory controllers differently? Maybe lack of AMD IOMMU support in the i386/i686 kernel? > > Where would I find official warnings about memory-size mixing? We can > bring it up with the vendor. The motherboard manual doesn't have such > caveats. Is this oral tradition? I had problems POSTing on a Tyan 2881 with two 242 Opterons using RAM from the same vendor (4 sticks of 512MB) because two of them were a different batch. After getting those replaced with verified modules did I get my 2GB worth of RAM.