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Started by drwoodcomb | | 13 answers
Can I run two GTX 970 in SLI using 16X/8X PCI Gen 3.0
I just bought an X99 chipset motherboard with an i7-5820K processor. Since its a 28 lane processor I assumed that I would be able to run one of my GTX 970s with 16x and the other GTX 970 at 8x. When I look in the BIOS is says they are both running at 8X. I contacted my motherboard manufacturer and the woman at ASUS said that there is no way to make one run at 16X and the other at 8X. She said that they both have to run at 8X. Is this true or is she full of it and doesn't know what she is talking about
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October 18, 2014 8:35:32 AM

Hope you get a replacement soon :)  I haven't OC'd my 970s yet. I do have my 5820K @ 4.4ghz. It's probably as high as I'm going at least for now due to high temps running Realbench (91C on Noctua 140mm Tower cooler). I tried 4.5, but it wasn't stable at the voltage I'm at now(1.325 wasn't enough even when I had ram at stock 2133 and Uncore at stock). I'm waiting for 970 waterblocks to become available first so I can integrate this new setup into my WC loop. For Ram, I got a 16GB Kit of Corsair Dominator Platinum 2800 Modules.
October 17, 2014 8:06:18 AM

1LiquidPC said:
Glad to hear from you again. I was wondering how things were turning out. That is pretty strange indeed. I don't think I've heard of that happening before, but some sort of strange defect in the card would explain why with your setup being pretty much that same as mine as far as motherboard, cpu,and 2 970s in the same slots would make one of your cards only be half of what it should be no matter the arrangement. I would probably contact the vendor/RMA like you mentioned and tell them your situation. Maybe try the card in another motherboard if you have it just for kicks. The fact that you swapped the cards and the lanes/slots work fine with card 2 and not card 1 should eliminate the motherboard as the cause. Let us know how this turns out.


I contacted ASUS and they said that the card is most likely defective. I got an RMA from newegg but since they are out of stock who knows when I'll ever get a replacement.

This is a little off topic but have you had the chance to overclock anything. Id be curious to compare notes to see how I stack up. Also what RAM did you get?

I'm new to forums. Changing the subject is considered a bad thing to do right? I could maybe start a new thread just for 5820k
October 14, 2014 2:40:40 PM

Glad to hear from you again. I was wondering how things were turning out. That is pretty strange indeed. I don't think I've heard of that happening before, but some sort of strange defect in the card would explain why with your setup being pretty much that same as mine as far as motherboard, cpu,and 2 970s in the same slots would make one of your cards only be half of what it should be no matter the arrangement. I would probably contact the vendor/RMA like you mentioned and tell them your situation. Maybe try the card in another motherboard if you have it just for kicks. The fact that you swapped the cards and the lanes/slots work fine with card 2 and not card 1 should eliminate the motherboard as the cause. Let us know how this turns out.
October 13, 2014 3:34:21 PM

1LiquidPC said:
I do have SLI enabled in the Nvidia control panel. For the UEFI, I actually didn't do anything. My first power on after installing both cards took a good bit longer than usual to post. I'm guessing this was for the board to recognize and configure the new cards. Booting up afterward was back to normal speed. I installed both cards at once. I removed my GT 610 "tester" card which I'd been using in this board for a few weeks. Once I was in the UEFI after installing the cards, it was already set to 16X on one slot and 8X on another. I didn't have to adjust anything myself. After that, in Windows 8.1, I just installed the 344.16 drivers and enabled SLI. This cpu/board combo definitely supports 16X/8X simultaneously. I'm running GPU-z 0.7.9 right now and flipping back and forth between the 2 cards, one says PCI-E 3.0 x16 @ x16 3.0, the other says PCI-E 3.0 x16 @ x8 3.0. Even with 16 + 8 that only 24 out of the 28 lanes used. Regular Haswell chips (4770k, 4790k, ect) only have 16 lanes total available, so if you ran 2 cards, you would only be able to do 8 + 8. Are you on the latest UEFI version from Asus, which is 0904?? Also, if you can look, what does it say under NB PCI-E Configuration in the UEFI on your computer. It's under the System Agent Configuration section under the Advanced tab. This is where mine says 16X and 8X. EDIT.. Just rebooted to check again under GPU Post in UEFI, mine says NVIDIA GPU connected natively at 16x in PCIE Slot 1 and NVIDIA GPU connected natively at 8x in PCIE Slot 4. Just had another thought, do you have any other cards(RAID HBA, Soundcard, ect.) plugged into the remaining PCI-E slots other than the 970s?? This may affect the number of lanes that are being assigned to the cards themselves.


Ok so I did some swapping of my video cards and something really interesting/weird is happening. Since I have two identical GTX 970 I will just refer to them as #1 and #2. First, I took out #2 so that only #1 remained in my computer. When I did that it ran at 8X. When I ran only #2 it ran at 16X. When I ran #1 and #2 it ran at 8X,8X. When I switched them around it ran at 16X,4X. So to recap:

#1 only : 8X (It should be running at 16X)
#2 only : 16X (This card is running at the correct 16X)
#1 and #2 : 8X,8X (It should be running at 16X,8X)
#2 and #1 : 16X,4X (It should be running at 16X,8X)

So basically from what I can tell, it appears that video card #1 is consistently running at half the speed it should be, no matter which way I set it up. I'm think that maybe its defective in some way?
October 11, 2014 10:41:19 AM

I do have SLI enabled in the Nvidia control panel. For the UEFI, I actually didn't do anything. My first power on after installing both cards took a good bit longer than usual to post. I'm guessing this was for the board to recognize and configure the new cards. Booting up afterward was back to normal speed. I installed both cards at once. I removed my GT 610 "tester" card which I'd been using in this board for a few weeks. Once I was in the UEFI after installing the cards, it was already set to 16X on one slot and 8X on another. I didn't have to adjust anything myself. After that, in Windows 8.1, I just installed the 344.16 drivers and enabled SLI. This cpu/board combo definitely supports 16X/8X simultaneously. I'm running GPU-z 0.7.9 right now and flipping back and forth between the 2 cards, one says PCI-E 3.0 x16 @ x16 3.0, the other says PCI-E 3.0 x16 @ x8 3.0. Even with 16 + 8 that only 24 out of the 28 lanes used. Regular Haswell chips (4770k, 4790k, ect) only have 16 lanes total available, so if you ran 2 cards, you would only be able to do 8 + 8. Are you on the latest UEFI version from Asus, which is 0904?? Also, if you can look, what does it say under NB PCI-E Configuration in the UEFI on your computer. It's under the System Agent Configuration section under the Advanced tab. This is where mine says 16X and 8X. EDIT.. Just rebooted to check again under GPU Post in UEFI, mine says NVIDIA GPU connected natively at 16x in PCIE Slot 1 and NVIDIA GPU connected natively at 8x in PCIE Slot 4. Just had another thought, do you have any other cards(RAID HBA, Soundcard, ect.) plugged into the remaining PCI-E slots other than the 970s?? This may affect the number of lanes that are being assigned to the cards themselves.
October 11, 2014 10:19:26 AM

1LiquidPC said:
Which slots in particular are you using?? I'm asking cause I'm basically using the exact setup as i'm typing this. I'm using an Asus X99 Deluxe motherboard, a 5820K, and 2 970s in SLI. I'm running at 16X and 8X GEN3 just like your asking about. I've confirmed it in both the UEFI and checking GPU-Z. I have 1 card in the usual top slot and the second in slot 5(second slot up from the bottom). This setup is the way it's recommended in the manual for the 5820K. Also do you have the most up to date UEFI? Hope this is helpful.



That is so weird! My cards are in the exact same slots as you. If you go into the NVIDIA Control panel, do you have SLI turned on? When I look in GPU Post in the UEFI it says they are both running at 8x. Did you enable or disable anything in the UEFI to get it to do that? I am really confused because I read benchmarks where people run two NVIDIA video cards in SLI at 16X/8X but then I hear some people saying that they will only run at the highest, matching speed possible. So since both our computers have 28 lanes it would be 8X/8X because 8+8=16. They cant both running at 16X/16X because 16+16=32. 32 is over the 28 lane limit. This is getting to be very frustrating and confusing.
October 11, 2014 6:40:43 AM

Which slots in particular are you using?? I'm asking cause I'm basically using the exact setup as i'm typing this. I'm using an Asus X99 Deluxe motherboard, a 5820K, and 2 970s in SLI. I'm running at 16X and 8X GEN3 just like your asking about. I've confirmed it in both the UEFI and checking GPU-Z. I have 1 card in the usual top slot and the second in slot 5(second slot up from the bottom). This setup is the way it's recommended in the manual for the 5820K. Also do you have the most up to date UEFI? Hope this is helpful.

a b V Motherboard
a c 81 U Graphics card
October 11, 2014 1:58:59 AM

Entomber said:
SLI makes both run at the slowest (maximum) speed available.

Are you sure about that? That certainly wasn't the case back in the 400 series days, as you could definitely run x16/x8 SLI, and the cards would show up in GPU-Z with the correct lane count (HardOCP did an entire feature comparing x16/x16 to x16/x8).

To the OP, are you sure you have the cards in the correct slots for x16/x8? In the 1st and 4th x16 PCIe slots? With both installed there should be a two slot gap between your two cards.
a b V Motherboard
a b U Graphics card
October 11, 2014 12:21:07 AM

if you did not have them in SLI then they would both run at the fastest speed possible. However, one would simply be used as a PhysX card (a waste of a GTX 970)
October 10, 2014 5:18:37 PM

The motherboard is an ASUS X-99 Deluxe Motherboard. The CPU I paired with this motherboard allows for 28 PCI-E express lanes. I have had little luck finding information on the internet to confirm what Entomber is saying. I just dont understand why the motherboard specs say that if you use two video cards that one will run at 16x and the other at 8x. Is this the case only if you use AMD video cards? Below I have copy and pasted the specs directly from the motherboard website. They should put an asterix(*) next to the spec that says the if you use NVIDIA cards that they both need to use the highest matching speed.

28-Lane CPU-
3 x PCIe 3.0/2.0 x16 (x16, x16/x8, x8/x8/x8)

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