>hey, I thought mixing dimm sizes was verbotten on opterons? Thanks for everyone's comments. I consulted with the person who has actually been working on the hardware. He says these motherboards have six slots for DIMM's, not 8, but they are supposedly in GT24 chassis, which come with K8SRE boards. So it's not clear what's going on; I may be misreporting the motherboards. There are mixed sizes per board: 4 1GB and 2 2GB. During testing, we did try removing the 2GB DIMM's, but did not rebalance the memory. We are physically away from the machines, so we'll take a closer look in the morning, and try some other configurations. The x86_64 vs. i386 difference is odd; maybe they treat the memory controllers differently? 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? Dan