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We have a Supermicro X7DWN+ motherboard with two Xeon L5420 CPU's installed. There is a total of 14GB memory installed, however the BIOS is only seeing 10GB.

The memory has been tested in another X7DWN+ and all 14GB is visible. The CPU's have been swapped with another server, they both work. The board is brand new, we had an old one that has exactly the same problem.

The power distribution board has been swapped.

I am really at a loss as to what the problem is here. The BIOS version is the same as other X7DWN+'s we have.

There is a mixture of 2GB and 1GB dimms installed. If I remove all the 2GB dimms and just leave the 1GB's, I only get 50% of the installed memory detected by the BIOS.

Suggestions as to what to try next welcome!?

Thank you.

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If the board is brand new, what does your distributor or Supermicro say? Is the BIOS/UEFI version the same? – Keith Stokes Feb 2 '13 at 20:41
Not talked to them yet, I replaced the board because all indicators suggested it was a board problem. I.e. the RAM and CPU were swapped with other working systems. The BIOS version is the same. UEFI is too new for this board. – SnAzBaZ Feb 2 '13 at 22:15
This can be caused by a damaged CPU socket pin. Is there a particular channel whose memory is not detected? – David Schwartz Feb 2 '13 at 22:39
Looking at memtest today, it is not seeing DIMMS installed in Bank C and Bank D, according to the manual these are both assigned to Branch 1. Bank A and B are in Branch 0. The CPU was my first idea, I will have to do more testing with swapping CPU's around. – SnAzBaZ Feb 3 '13 at 9:28
That sounds like damage to the CPU socket. – David Schwartz Feb 3 '13 at 19:39

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