I have a situation where I have a system with 16 GB of physical RAM, but at the BIOS level only 8 GB are detected. There are 4 sticks of G.Skill Ripjaws 4 GB DDR3 1600 MHz RAM. The motherboard is an ASUS P8B75-V LGA 1155 with an Intel Core i7-2600K Sandy Bridge. I built this system in 2012.
I have taken all RAM sticks out and then one by one I have tested them individually on all RAM slots on the motherboard. All sticks work on all slots and 4 GB is detected by the BIOS. All RAM sticks seem to be good and so are the RAM slots on the motherboard. Only when I have more than 2 sticks inserted is when the BIOS does not detect anything beyond the 8 GB.
My OS is ArchLinux, but that is not relevant here because the BIOS does not detect the full 16 GB of RAM.
Any ideas or obvious settings that I am missing in the BIOS configuration?