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I installed a single Opteron CPU into a dual-socket mainboard Super Micro H8DGi-F and now I'm facing the problem that I can only use one PCI-e 16x slot, although there are 3 of them on the board. I've plugged in multiple video cards, but there's only one that is recognized by the OS.

In the manual (on page '1-9') I found a diagram showing "SLOT#6 PCIE (X16)" connected to "SOCKET #1", while the other two PCIE (X16) slots "#2" and "#4" are connected to "SOCKET #2" only.

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Does this mean, that I can't use more than one PCIe 16x video card as long as there's only one CPU mounted on the board?

Thanks!

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up vote 4 down vote accepted

Does this mean, that I can't use more than one PCIe 16x video card as long as there's only one CPU mounted on the board?

Yes.

Note that you can also only use half the the memory banks.

This is because part of the PCIe lanes and part of the memory banks are routed to a specific CPU. If that CPU is not present then you can not use it. (This is because the modern CPU contain the PCIe and the memory controllers).

[Edit]

Note that you can use multiple PCIe cards (including up to three graphical cards) if you have a single installed CPU and you use slots 3, 5 and 6. Those provide x4, x8 and x16 lanes.

Using all x16 lanes for a card is more or less standard, but there is no theoretical reason why you can not put a graphical card in a smaller length slot. It will be slowly slower (around 5-10% for most midlevel cards, see benchmarks on tomsHardware, Anandtech and similar sites) but it will work.

The real downside is that not all smaller connectors are open ended and that you would need to use a saw on a very expensive motherboard. Not something to do recklessly.

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Thank you for your clear and detailed answer! –  Pavel Jan 8 '13 at 18:12
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