Motherboard PCI slot for GPU / gpu perfomance issue

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k400123

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Aug 14, 2017
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Hello.

I have a Asrock Z77 Pro-4M mobo which has 3? slots for GPU and I was wondering does it matter where I put my GPU ?

I have a MSI 970 card and I can't fit it in the first slot beneath the CPU because my memory sticks are to high so the only option I have is the second and third.
Due to how I packed the rig I could fit it in the second slot by moving my ssd but didn't really want to bother so I put it in the third slot.

Today I tried out Project Cars 2 @1080 and noticed on ultra settings I got max 80FPS with average of 60-65 but I watched a few youtube videos where people get easy 100+ AVG on the same settings and resolution. The CPU isn't bottlenecking as it's not used more than 60% when playing so I thought maybe it's the PCI slot I put my GPU in that's not allowing it to perform as it can? Everything is on stock clocks.

I read this in the mobo manual but didn't really understand it.

- 1 x PCI Express 3.0 x16 slot (PCIE1: x16 mode)
- 2 x PCI Express 2.0 x16 slots (PCIE3: x1 mode; PCIE4: x4 mode)
- 1 x PCI Express 2.0 x1 slot

Heres GPUZ screenshot; it says PCIe x16 2.0 @ x4 2.0
https://image.ibb.co/inDDdk/123.png

Thanks in advance!

Rig:

PSU: Thermaltake Litepower 650W LT-650P
CPU: i7-3770
Mobo: ASRock Z77 Pro4-M
GPU: MSI Gaming GeForce GTX 970 4GB OC
RAM: Transcend 2x8GB @1333Mhz
SDD: Kingston HyperX Savage 480GB SSD
 
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drinkingcola86

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The Answer is yes and no.

Yes it does matter, you should put it in the slot that has the PCIE 3.0.

No, it doesn't matter because that video card doesn't saturate the PCIE 2.0 band width. What you might run into though is that if you put it in the 2.0 slot, it might not see it until something is in the PCIE 3.0 slot.
 
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Chaos2Theory

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i think its safe to say its probably in the wrong slot, i'm looking at the diagrams for the motherboard and it seems that the last one is not supported at a fast enough speed. ideally you should use the first slot with this motherboard, so as to get full pcie 3.0 performance, but 2.0 16x is good enough.

Important note, unlike what the person above me said, only the first 2 slots are capable of 2.0 16x or 3.0 16x the last one seems to be locked at a max of 2.0x4 max? Its hard to tell exactly but something like that.
 
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Roland Of Gilead

Roland Of Gilead

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Aug 8, 2008
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according to the specs, slots 2 and 3 are PCIE 2.0 so you should be able to run the card just fine in those. PCIE 3.0 has more bandwidth, but PCIE 2.0 is still plenty to saturate even the high end cards of today. The decrease in bandwidth for 2.0 has been shown to have practically no effect on gaming.
Ideally you want it in the primary slot, but in this case it shouldn't have much if any affect.

On the game itself, Project Cars 2, I've not played it so I can't really be specific. It depends on what res you are playing. I've a similar performing machine, roughly speaking, and I'd expect my results to be similar based on how Project Cars 1 performs on my system. Not exact confirmation of your question, but rather a loose guideline.
 
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iamacow

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Seems like people are confused here so I'll clear it up. The bottom line is the first slot is 16x and the rest are 4x. The picture shows the second 16x slot being wired for 8x but if the specs say it will only run in 4x and you are getting 4x, than I would say its correct. You need to put in the first slot or suffer some frame rate issues.



This is a bogas statement, PICE 3.0 has less of a problem with this because 4x 3.0 is equivalent to 8X PCIE 3.0. You get down to 4x 2.0 and you are SOL for most games as games in 2017 can eat up 8x 3.0 / 16x 2.0 like its nothing.
 
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k400123

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Yes I've just updated the thread, it looks like its in the 2.0 x4 slot. I don't know how much of a problem that is as I don't really understand what it means.
 
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Roland Of Gilead

Roland Of Gilead

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Well done first on the 4x spot. I didn't catch that so I agree that would definitely impact the performance on the card.

Regarding the difference between 2.0 and 3.0 i was referring to 16x by speeds and there being no difference. I've seen the testing done, Ill try find it and link it. It was on Anand or Tom's some time ago.

Obviously there is a difference at 4x 16x and the impact on the GPU.


 
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rolli59

rolli59

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card will loose between 10-15% of its performance in a 2.0 X4 slot versus a full 3.0 X16 slot https://www.techpowerup.com/reviews/NVIDIA/GTX_980_PCI-Express_Scaling/21.html
I have never heard of ram slots blocking the top X16 slot which is the default GPU slot on most if not all boards since the card does go down from the slot not up. Suggest getting ram that does not hang over the ends of the slot.
 
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gasaraki

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God, please people stop answering questions if you don't know what you are talking about.

The slot you are using right now IS affecting your performance. Going from (PCIe 3.0 16x - 15.8GB/s) to (PCIe 2.0 4x - 2GB/s) IS going to affect performance.

So freakin funny that people are saying going from 15.8GB/s to 2GB/s is not going to affect performance.
 
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iamacow

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Agreed. It may not have any effect on older games or some @ 1080P. But a new game like Project Cars 2 is going to take a huge hit in a PCIE 2.0 4x SLot. The article is older games, abeit it is a 980 and the OP has a 970. Other than this single article is has been shown time and time again that 4x PCIE 2.0 is simply not enough bandwidth.

I guess we all got sidetracked because if the Op said seeing 100+ in the same game on Youtube, how do you know its the same video card? the 970 has 4GB of vram and I think on ultra settings that games uses 6GB. I think more is at play here than a 4x slot.
 
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13thmonkey

13thmonkey

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That was my expectation, however the graphs in the link a posts up are useful to understand the size of the issue, and it's a lot less than I expected. I was thinking that most people were thinking x16 and not seeing the x1 and x4 electrical.
 
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k400123

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Thanks everyone for responses. I've now moved it to the second slot and weirdly GPUZ now says its @x1 2.0. I've tried PCars2 again and I think I lost ~20fps in this slot. Where it was lowest 65FPS its 45 now not sure about highest.

So I guess I'll just return it to third slot as I'm not looking to buy new ram sticks right now. It wasn't even that bad in the third slot it was just weird seeing people with the same card getting 30 avg more fps and I'm not even sure the first slot would make that big of a difference. Might be a problem somewhere else.

I noticed my card won't draw more than 80% power under full load so it might be that.
 
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iamacow

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K400 is the top slot is the only real 16x slot. If you cannot put the card there than leave it in the second 16x because at least that's 4x.

Top- 1 x PCI Express 3.0 x16 slot (PCIE1: x16 mode)
Middle / Bottom- 2 x PCI Express 2.0 x16 slots (PCIE3: x1 mode; PCIE4: x4 mode)
- 1 x PCI Express 2.0 x1 slot
 
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