Question PCIe lanes question

ar_0

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So, this is all hypothetical.

If I had a 9900k processor with two RTX 2080 TIs, an NVMe drive, and a few more SATA SSDs, the total PCIe lanes needed would be way more than 20, right? But the processor supports only up to 16? How would this work? How would gaming performance be affected? And how would other production software be affected, such as using adobe premier?

And to be more specific about gaming performance, what's the advantage of having two RTX 2080 cards utilizing 8 lanes each vs a single RTX 2080 utilizing all 16 lanes in terms of pure numbers, not actual gaming performance, because I realize that, in reality, every game would be different.
 

Math Geek

Glorious
Herald
all depends on how the mobo spreads out the lanes. normally you get 16 for the main pcie slot and then 4 for the mvme slot. any extra pcie cards start splitting up the 16 lanes as you add.

you have to look at the specific mobo as to how it works. uing one port/slot usually turns off another one. so there is always a trade-off.

high end expensive boards can add an extra chip that adds more lanes and controls how they get directed to the cpu. but again all of this is very mobo specific.

as for using a 2080 at x8 is not a problem at all. the cards don't saturate 8 lanes and won't see any difference that way. the advantage of using one card over 2 is getting the second card to work. you don't get double the performance and often the second card can actually lower what you would get from a single card.

sli is dead and not worth even trying to work with anymore. it's just DEAD!!!
 
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jimmysmitty

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The CPU itself has technically 20 total with 4 being used for DMI specifically, to connect to the chipset and other inputs. The CPU has 16 total available for PCIe slots and are usually distributed among the PCIe x16 slots exclusively for use with mainly GPUs. SO running 2 2080 Tis would result in two x8 PCIe 3.0 slots.

The chipset itself has 24 of its own PCIe lanes to be used for other features such as a NVMe drive, faster NIC. USB 3.1 etc. They do not affect the CPUs PCIe lane count.

Right now no single GPU, consumer gaming card, saturates a PCIe 30. x8 lane let alone a PCIe 3.0 x16 lane. The benefit for two cards is potentially double the gaming performance however the game has to be coded for it and optimized and right now SLI does not have as much support as it once did since single GPUs are capable of 4K 60FPS gaming, such as the RTX 2080 Ti.

In laymans terms, multi GPU setups like SLI or Crossfire are currently not worth it due to the low support and potential issues that come with it.
 
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Dunlop0078

Polypheme
Herald
The GPU's will only use the 16 lanes from your CPU so they will run at x8, x8. The NVME drive will use lanes from the chipset on the motherboard, so using an NVME drive will not take lanes away from the GPU's.

In a game with proper SLI support which is quite rare nowadays 2 2080 ti's in sli at x8 will offer significantly better performance than a single 2080 ti at x16. 8 pcie 3.0 lanes should not significantly bottleneck a 2080 ti if at all. versus 16.

I have no idea how something like adobe premiere would be affected. In terms of a benchmark like firestrike extreme or something, two 2080 ti's in SLI X8 would crush a single 2080 ti at x16.
 
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ar_0

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all depends on how the mobo spreads out the lanes. normally you get 16 for the main pcie slot and then 4 for the mvme slot. any extra pcie cards start splitting up the 16 lanes as you add.

you have to look at the specific mobo as to how it works. uing one port/slot usually turns off another one. so there is always a trade-off.

high end expensive boards can add an extra chip that adds more lanes and controls how they get directed to the cpu. but again all of this is very mobo specific.

as for using a 2080 at x8 is not a problem at all. the cards don't saturate 8 lanes and won't see any difference that way. the advantage of using one card over 2 is getting the second card to work. you don't get double the performance and often the second card can actually lower what you would get from a single card.

sli is dead and not worth even trying to work with anymore. it's just DEAD!!!
Thanks. The motherboard I have in mind is the Maximus XI Extreme. I guess I'll have to download a manual then. And the reason I mentioned SLI is because the software I want to use is P3D v4, which is a flight simulator, for those who never heard of it. SLI might be old for modern games, but P3D is based on FSX, another simulator released in 2006, and P3D still carries much of FSX's limitations. A recent bench marking with the RTX 2080 revealed that SLI in some cases does indeed lower FPS, but when using maximum settings, SLI with the RTX2080 does actually improve performance in P3D. That's why I was asking. Something to keep in mind for the future, the near future I hope.

Thanks so much. If you have anything to add, I'm willing to learn more.
 
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ar_0

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The CPU itself has technically 20 total with 4 being used for DMI specifically, to connect to the chipset and other inputs. The CPU has 16 total available for PCIe slots and are usually distributed among the PCIe x16 slots exclusively for use with mainly GPUs. SO running 2 2080 Tis would result in two x8 PCIe 3.0 slots.

The chipset itself has 24 of its own PCIe lanes to be used for other features such as a NVMe drive, faster NIC. USB 3.1 etc. They do not affect the CPUs PCIe lane count.

Right now no single GPU, consumer gaming card, saturates a PCIe 30. x8 lane let alone a PCIe 3.0 x16 lane. The benefit for two cards is potentially double the gaming performance however the game has to be coded for it and optimized and right now SLI does not have as much support as it once did since single GPUs are capable of 4K 60FPS gaming, such as the RTX 2080 Ti.

In laymans terms, multi GPU setups like SLI or Crossfire are currently not worth it due to the low support and potential issues that come with it.
Thank you so much. This was very informative.
 

ar_0

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The GPU's will only use the 16 lanes from your CPU so they will run at x8, x8. The NVME drive will use lanes from the chipset on the motherboard, so using an NVME drive will not take lanes away from the GPU's.

In a game with proper SLI support which is quite rare nowadays 2 2080 ti's in sli at x8 will offer significantly better performance than a single 2080 ti at x16. 8 pcie 3.0 lanes should not significantly bottleneck a 2080 ti if at all. versus 16.

I have no idea how something like adobe premiere would be affected. In terms of a benchmark like firestrike extreme or something, two 2080 ti's in SLI X8 would crush a single 2080 ti at x16.
Thank you. I brought up Premiere because I thought graphic cards would take PCIe lanes away from an NVMe drive, which I assumed would affect Premier's performance when rendering, for example. But I understand now that that's not the case. Correct?
 

Math Geek

Glorious
Herald
normally, the 20 lanes are divided up giving 4 to the main m.2 slot. so you should be ok there. you are right though, reducing lanes to the m.2 slot will affect performance. but that should not happen.

do note though, that you usually give up some sata ports to use the m.2 so check the manual carefully to be sure the combination of drives will be supported.
 
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ar_0

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normally, the 20 lanes are divided up giving 4 to the main m.2 slot. so you should be ok there. you are right though, reducing lanes to the m.2 slot will affect performance. but that should not happen.

do note though, that you usually give up some sata ports to use the m.2 so check the manual carefully to be sure the combination of drives will be supported.
Thanks. I appreciate all the help.
 

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