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P55 and PCI-E limits

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January 14, 2010 4:48:19 PM

I'm planning an upgrade to a P55 platform and have a few questions. I've searched pretty extensively and have seen conflicting statements on this so I'm just as confused as before...

First - I have noticed that some mobos, such as the P7P55D Deluxe, are listed as supporting auto switching between x16/x1 and x8/x8 operation for the two primary (CPU-related) PCI-E x16 slots. In the former scenario, will the second slot actually operate in x1 mode if I put, say, a x1 sound card in it? Or will ANY card in the second slot drop things down to x8/x8? If the latter, even if it's just semantics, why isn't it referred to as x16 with the second slot disabled?

Second - I understand that given the limitations of P55, the PCH provides 8 PCI-E 2.5GT/s lanes and that some of these are used for onboard devices. The third PCI-E x16 slot typically runs at a x4 electrical link, which is provided by the PCH. My question here is, if I were to populate the first two PCI-E x16 slots with graphics cards, and populate the third (x4) slot with a card for PHYSx, what would typically happen to any remaining x1 slots on the mobo (I expect some variance between different models and manufacturers)? Since the remaining number of P55-provided lanes would be 4, I would imagine that the SATA and an ethernet controller would take 2, leaving up to 2, so in theory it should be possible to use a x1 sound card in one of the x1 slots, provided I'm not using an additional SATA controller or second ethernet controller. Am I correct in this?

Hopefully some of you can speak from experience as I'd prefer to fully understand what I'm getting into before actually buying parts and hoping works like I expect...

Thanks!

More about : p55 pci limits

a b V Motherboard
January 14, 2010 8:33:24 PM

The way I read the motherboard manuals a graphics card in the second slot is what triggers x8/x8 mode, not some other kind of card. The new motherboards with USB3 also have to contend with that extra drain on the PCIE channels and I have not researched exactly how they operate yet.
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January 14, 2010 8:35:53 PM

1156 systems dont scale well when using crossfire/sli. If your going to be using more than one card then get a 1366 system. when your using 3 video cards in a 1156 system it drops down to 4x/4x/4x which is horrible and will preform worse than a single card.

If your going 2 cards and 8x/8x its not too bad and performs better than 1 card. But 3 video cards is a no no on 1156 system its just not built to handle that. 1 video card on a 1156 platform is perfectly fine though.

And if im understanding what your asking correctly no your on board sata/ethernet do not use up your pci-e bandwidth.
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February 21, 2010 3:09:43 PM

but if 1156 based processors got more pci-e lanes, let's say the double (now they have 16 and 2x of that would mean 32)
will he be able to run two graphicscards in 16x/16x ? and /Or sli with physX with 16x/8x/8x ??
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a b V Motherboard
February 22, 2010 5:06:21 PM

Meatwipe said:
but if 1156 based processors got more pci-e lanes, let's say the double (now they have 16 and 2x of that would mean 32)
will he be able to run two graphicscards in 16x/16x ? and /Or sli with physX with 16x/8x/8x ??

It would not be an 1156 based CPU anymore. It would be a different architecture and not fit in a P55 motherboard. Its a physical limitation from how intel designed it.
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