I learned something today. From this thread I learned that there is a side-effect to the PCI-X architecture that I wasn't aware of. Apparently the BIOS reserves a portion of RAM for its use. If your RAM is close to or at the 4GB line, you can get memory in Extended Memory even though you are not actually crossing the 4GB barrier. So I go check our servers.
It could be worse. Apparently Dell BIOS reserves the top 1GB!
The "Extended Server memory" line is the key one. Extended server memory is a lot slower than regular "server memory" due to the 32-bit limitation in RAM. To use extended, memory has to be paged from extended, down below the 4GB line, manipulated, then paged back. Hardly efficient. And as I remember from Brainshare, all 32-bit operating systems have this problem. NetWare can support RAM over 4GB... but you'll need a lot of it to get much performance benefit from it. Same for Windows and Linux. Obviously 64-bit operating systems don't have this problem.FACSRV1:memory
Total server memory: 3,669,577 Kilobytes
Total Extended Server memory: 458,748 Kilobytes
It could be worse. Apparently Dell BIOS reserves the top 1GB!