Blackford PCIe configuration - need a sanity check

AreEss

2[H]4U
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Okay, this has me seriously scratching my head right now, so I wanna run it by folks who might know the board better. (I haven't touched this one yet.)

http://www.intel.com/design/servers/boards/s5000VSA/index.htm
Intel S5000VSA - 2x PCI-X/133, 2x PCIe 8x Physical/4x Electrical

Now this has me seriously scratching my head. First of all, when using only one slot, does that PCIe slot go to 8x electrical or did they only lay traces for four lanes of signal and eight lanes of power? And yes, I know that 5000V only has 8 PCIe lanes.
 
I'd be awfully surprised if they ran all 8 lanes to one slot and put a check in hardware to see whether you had two cards in or not. Nothing I can see would lead me to believe it can work in that way - usually they designate them as "x4/x4 or x8" or something similar.
 
It's an 8x slot that operates at 4x bandwidth

Thank you, captain obvious.. that's what I said. You do realize I can take a 16x slot and operate it at 1x even if it's wired for 16x, right? (Seriously, you can.) Very much not the question here.

unhappy_mage said:
I'd be awfully surprised if they ran all 8 lanes to one slot and put a check in hardware to see whether you had two cards in or not. Nothing I can see would lead me to believe it can work in that way - usually they designate them as "x4/x4 or x8" or something similar.

Why? It's trivial and how do you think dual 8x SLI works when the route PCB or jumpers aren't present? They only check for one lane of signal and split irregardless of the card's actual lane use. (This can be corrected after boot in driver if you wanna be silly.)

IOW; there's absolutely no reason Intel can't wire BOTH slots for a full 8 lanes, then electrically split. Or wire one 8 and one 4, then take off 4 when both are in use. However, after finding out just how ungodly broken the 5000-series interrupt controller is, I won't be going Xeon anyways. But the question remains.
 
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