Hi, I have a dual Opteron File server with 4GB ram, and just "upgraded" to SLES9 x86-64 (was previously running SUSE 9.3 x86-64 without problem). The system keeps crashing, and I am starting to suspect mtrr. Some other posts on the subject indicate that mtrr is used to remap the memory that is hidden by the PCI bus to a region above the existing physical memory, so it can be accessible. The system on boot always reports something like this: mtrr: 0xfd000000,0x800000 overlaps existing 0xfd000000,0x400000 mtrr: 0xfd000000,0x800000 overlaps existing 0xfd000000,0x400000 And after running a while it suddently locks up, requiring a cold start. Something else that I thought funny is that there are 2 PCI -X cards in it that work fine but attempting to put in another (an Intel dual GigE card) prevents the system from booting or even passing POST (even with the other cards removed). The same card works in another dual Opteron machine (different mother board) running SLES9 without problem. So, if erroneous memory mapping by mtrr is causing the lockups, how can I remap or disable memory mapping? Thanks for any clues