Why MemTotal (and free total) don't match the actual RAM value of real configured memory

Solution Verified - Updated -

Issue

A question being asked more frequently as we move to larger memory configurations (>512GB) is why is the /proc/meminfo value for MemTotal (the same value presented by 'free' Total) so much smaller than the actual assigned RAM. From investigation of a 6TB and a 512GB server it has been determined what makes up that "difference". In the example of a 512GB configuration which is noted in the Diagnostic Steps, there was a variation of some 8GB unaccounted for. That is, on a 512GB memory system, MemTotal was reporting 503GB of available memory. As memory systems are getting larger, this variation is seemingly becoming more questioned. It is not however, a defect nor a problem as this article points out.

Environment

Red Hat Enterprise Linux - RHEL7
Red Hat Enterprise Linux - RHEL6
Red Hat Enterprise Linux - RHEL5

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