February 17, 2016

Only 8GB of 16GB RAM is used by Linux?

We have a Dell Xeon quadcore workstation which is installed with 16GB (2x8GB) DDR3 RAM but the Red Hat 5 OS shows only 8GB RAM when observe red in Memory and Swap History of the System Monitor utility. I have also verified the same issue with MS Windows Server 2012 R2 which shows total RAM of 16GB but usable RAM of 8GB.
Looking into the setup of workstation the total installed physical memory is indeed 16GB in two different slots. It was showing only 1 memory channel before but when I swapped the memory modules it is showing 2 memory channels. However, with this configuration the System Monitor utility of Linux is still showing 8GB of RAM.
Why this is happening and, is it a hardware or OS issue?

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