I just built a new system that I plan to use as a VM host (running ESX 5.1):
MB: MSI 990XA-GD55
CPU: AMD FX 8320 8 core
The BIOS shows all 32GB of RAM, however, when I run ESX, Centos or Fedora, they all show 16GB of RAM. I read that the AMD CPUs have an integrated memory controller. I'm wondering if my CPU is causing the issue? Oh yeah, I also tried booting with 16GB and the OS's showed 8GB.