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Will PCIe 3.0 affect the amount of PCIe 2.0 lanes?

Go to solution Solved by Oshino Shinobu,

You seem to be misunderstanding how PCIe lanes work a bit. The CPU provides lanes and the board has PCIe connections that utilise those lanes, but it doesn't provide lanes for each connector on its own. The chipset on the motherboard will provide some lanes as well (the amount depends on the chipset). 

 

Typically, CPU lanes are reserved for high bandwidth devices. This basically works out to be reserved pretty much always for graphics cards. Things like storage, add in cards and such will run off the chipset's lanes. 

 

Your Thunderbolt add in card should take up some lanes from the chipset, not the CPU, meaning the graphics card's lanes will be unaffected. Even if it did take some CPU lanes and dropped the GPU down to PCIe 3.0 x8, it wouldn't impact performance as the GPU can't fully utilise PCIe 3.0 x8 anyway. 

So my CPU (i7-4790k) gives 16 lanes and my mobo (ASRock H97M PRO4) offers 1 PCIe 3.0 x16, 1 PCIe 2.0 x16, 2 PCI. My 1080 ti takes up 16 lanes of the PCIe 3.0. Would adding a Thunderbolt 2 AIC which takes up PCIe 2.0 x4 effect the performance of my 1080 ti with its PCIe 3.0 x16? If so, how much of an impact would it have? What if it was Thunderbolt 3 AIC which uses PCIe 3.0 x4? 


I'm not sure which category this question belongs in, so apologies in advance if I placed it in the wrong one. 

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The lanes are shared the version is just the max bandwidth that the lane/slot can offer. By installing a second card it should bring your 1080ti to PCIE 3.0 x8, which still should not bottleneck your GPU or affect performance (unless a 1080ti is fast enough it will in which case that is news to me).

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You seem to be misunderstanding how PCIe lanes work a bit. The CPU provides lanes and the board has PCIe connections that utilise those lanes, but it doesn't provide lanes for each connector on its own. The chipset on the motherboard will provide some lanes as well (the amount depends on the chipset). 

 

Typically, CPU lanes are reserved for high bandwidth devices. This basically works out to be reserved pretty much always for graphics cards. Things like storage, add in cards and such will run off the chipset's lanes. 

 

Your Thunderbolt add in card should take up some lanes from the chipset, not the CPU, meaning the graphics card's lanes will be unaffected. Even if it did take some CPU lanes and dropped the GPU down to PCIe 3.0 x8, it wouldn't impact performance as the GPU can't fully utilise PCIe 3.0 x8 anyway. 

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2 minutes ago, suchamoneypit said:

The lanes are shared the version is just the max bandwidth that the lane/slot can offer. By installing a second card it should bring your 1080ti to PCIE 3.0 x8, which still should not bottleneck your GPU or affect performance (unless a 1080ti is fast enough it will in which case that is news to me).

It should run off the chipset, having to impact on the GPU's lanes. 

 

H97 chipset provides 8 PCIe 2.0 lanes in 1x, 2x or 4x modes. 

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Although this info is ultimately correct for this situation, it is to be noted for anyone else reading this, that it works a little different on Ryzen chips as there are a few more CPU lanes to dole out to other devices.  And in any case, you should probably read that little piece of folded paper (the manual) that came with your motherboard.  More often than not, it will tell you how many lanes are available in each configuration.

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