64GB RAM (only 51.9GB usable)

Turborudi · Sep 16, 2013

I recently built a PC for my 3D rendering and it has been giving me this problem since the start.
I have 64GB(8x8GB) RAM installed but in the BIOS some of the DIMMs shows up as 4GB. In Windows when I go to msinfo32 The PC says the following about my installed RAM:

Installed Physical Memory 64.0 GB
Total Physical Memory 51.9 GB

I have re-seated my CPU's, updated my BIOS and tried to identify if it may be faulty DIMMs by swapping them around and booting with 1 DIMM at a time but they all worked fine and showed up as 8GB when individually booted up with.

These are my system specs which I think could contribute to the problem

Asus Z9PE-D8 WS Motherboard (Dual CPU)
2x Xeon E2620 hexacore @ 2GHz
8x8GB Corsiar XMS 1333Ghz RAM
GTX690 (plugged into the 2nd true x16 PCIe port because it touches the CPU heatsinks in the 1st port.)
1300watt coolermaster silent hybrid pro PSU (according to Asus PSU calculator my system uses 1100watt power so I doubt that it's got something to do with insufficient power issues)

Pinhedd · Sep 16, 2013

Turborudi :

51.9 GiB out of 64 GiB is conveniently 12 GiB short of what you would be expected (a small amount, a little under 100MiB, is reserved for hardware).

8GiB UDIMMs (the kind found on consumer motherboards) are actually constructed as two separate 4GiB ranks, one on each side of the module. There is no electrical difference between two ranks each on a single rank DIMM installed in separate slots, and two ranks on a dual-rank DIMM installed in one slot. The only difference is where the chip select signal gets sent. Ergo, if one of the ranks fails, the other may work just fine. This can give the appearance of an 8GiB DIMM having only 4GiB, or a 4GiB DIMM having only 2GiB.

Seeing as you're 12 GiB short, I suspect that 3 ranks aren't operational. This could be caused by a bad connection in one of the DIMM slots, or a faulty DIMM.

iam2thecrowe · Sep 16, 2013

try removing half of the ram, and see if you get 32gb, then remove them and try the other half and see what happens.

Tradesman1 · Sep 16, 2013

Is this from a single package of DRAM or is it two packages of 32GB or 4 of 16GB, because if you're mixing packages, even of the same exact model it can be problematic....what actual model# of DRAM do you have

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64GB RAM (only 51.9GB usable)

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