Hi, I have a Linux distribution ( Oralce Enterprise Linux 5.3 i.e. Redhat ) that I have installed. It works fine when I used 2*512Mb dimms or replace them with a single 1Gb dimm. However when I try to go above 1 Gb the bootup and general performance deteriorates badly. The BIOS picks up the memory changes ok and I am using the same type of memory sticks. It makes no difference if I load a single memory channel with the 2 sticks or balance the sticks over the 2 channels. I have seen quite a few hits concerning problems with performance over 1Gb - any solutions ?
That is a bit strange. I can think of couple of things, first run memtest on both the configuration you mentioned, and compare results.
Check out memtest86.com. Even Ubuntu/Xubuntu boot DVD's can do that run memory test.
Second, check with your hardware vendor.
Would be nice to hear back about your memtest results. 
-Nitin
It is a common problem with RHEL 5.3 but as far as i know only above 2Gb.
Does the problem first manifest itself at /usr/sbin/loader during the boot process?
As an aside I had to remove 4 GB of DDR3 memory (out of a total of 6Gb) from a 64-bit system recently before the performance improved!
once I updated BIOS the performance improved but I am not convinced by the memory as every so often the server hangs for no apparent reason