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PCIE 3.0 Lanes

post #1 of 7
Thread Starter 
I am looking to buy the new ASUS X79-Deluxe, but the only thing stopping me is my lack of knowledge of how PCIE lanes work.

Due to other components of my setup, I am going to be unable to use the top PCIE lane. WIth the two dual slot graphics cards I am going to be using, I will then need to use the second and third PCIE slot. From what I have been reading, This will reduce my card speed to x8 for both of those cards. Here is a quote from the article I found

" PCIe x16 slots are carefully arranged to accept three dual-width cards in CrossFire or SLI. The first and second x16 slots can be configured with 16 lanes of PCIe 3.0 bandwidth from the CPU. For a three-way config, the second slot splits its lanes with the fourth one, yielding an x16/x8/x8 setup."

Am I right in assuming I would need to either suffer from the x8 speeds or find a different board, because using the top slot is not an option. Also, would an x8 speed really hinder me? from what I have read, PCIE 3.0 X8 is equivalent to PCIE 2.0 x16. and I have heard no graphics card yet utilizes the speeds of PCIE 3.0. For reference im using two ASUS HD7970-DC2-3GD5 with a custom watercooling block allowing them to fit in two PCI slots each....

It looks like my only other option is ASUS P9X79-E WS if the X79-Deluxe doesnt work out.

Any Help is appreciated!
post #2 of 7
Unless you're using a multi monitor setup - or you have a monitor above 1440p, you will not benefit greatly from the PCI-E 3.0 speeds. That's my understanding of how its down.

But you are right in what you are assuming though. When you take the third or fourth PCI-E lane in use, the second lane is divided.

One - 16x | One - 16x
Two - 16x | Two - 8x
Three - empty | Three - 8x
Four - empty | Four - 8x
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post #3 of 7
Thread Starter 
Im going to be running 4 monitors @ 1920x1080, so looks like I wont be getting this board :-/
post #4 of 7
Is it necessary for it to be an that exact board? You could also go with the Asus Rampage IV-E
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post #5 of 7
Thread Starter 
I looked at it and I believe it has the same issue, although I cant find anything that gets specific about the way the PCIE lanes are split up
post #6 of 7
I know that pci-e 3.0 x8 = pci-e 2.0 x16 ---which doesnt bottleneck a gpu at all beyond margin of error(+2-4%) so you should be fine. SB-E's extra pci-e lanes are the major benefit from how i understand it.
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some 25 dollar logitech  pfft Logitech 5.1 surround + sub  
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intel core 2 duo e8400 biostar tpower i45 some old 4000 series ati card that i didnt want... 8gb of gskill ddr2 800 
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post #7 of 7
PCI-E layouts are listed in the manual, which you can get from ASUS's site. But yeah, not using the top 16x slot on most any board will limit you to 8x/8x, or 16x/8x at best.

Performance difference with two cards should be completely trivial, however.
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