Can I run two GTX 970 in SLI using 16X/8X PCI Gen 3.0

drwoodcomb · Oct 10, 2014

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

Entomber · Oct 10, 2014

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

Wolfshadw · Oct 10, 2014

More than likely, the 16 PCI-E lanes are shared between the two PCI-Ex16 slots. If the second slot is not populated, the one card gets all 16 lanes. If the second slot is populated, it takes 8 lanes from the first PCI-Ex16 slot. If that's the case (you didn't tell us which board), then she's probably telling you the correct information.

-Wolf sends

Optimus_Toaster · Oct 10, 2014

They'll probably be running at 8x/8x mode.

But 8x/8x in 3.0 mode will make no difference.

drwoodcomb · Oct 10, 2014

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)

Entomber · Oct 11, 2014

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)

Damn_Rookie · Oct 11, 2014

Entomber :

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.

1LiquidPC · Oct 11, 2014

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.

drwoodcomb · Oct 11, 2014

1LiquidPC :

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.

1LiquidPC · Oct 11, 2014

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.

drwoodcomb · Oct 13, 2014

1LiquidPC :

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?

1LiquidPC · Oct 14, 2014

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.

drwoodcomb · Oct 17, 2014

1LiquidPC :

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

1LiquidPC · Oct 18, 2014

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.

drwoodcomb · Oct 31, 2014

1LiquidPC :

Hi Liquid PC,

I think I finally figured out what is causing my lack of 8X bandwidth on my 2nd video card and was wondering if you could help me out. Its a long shot and I completely understand if you don't want to do it since it would be a huge pain for you to undo part of your set up. I noticed some of the PCIe slots on my motherboard don't have pins running down their entire length. PCIe slots 1 and 3 do, but slots 2, 4, and 5 only have pins that go half way. Whats even worse is that if you look at the picture I have included below you can see that two of the pins on slot 4 are sticking out and aren't where they should be. That also happens to be the slot where my 2nd video card is. Is your motherboard the same way?I'd really appreciate any input you have on the matter.

Thanks

https://onedrive.live.com/redir?resid=C14549BE332BB5B%214581

1LiquidPC · Oct 31, 2014

Hello again, drwoodcomb

I did some searching on google and found an answer for you. If you look at the review of the x99 deluxe on kitguru.net(page 3 of review), you can see in the pictures the that pin arrangement is indeed halfway on some slots. Also, looking at my X99 deluxe while I'm typing this, I have the same pin arrangement too. My second 970 is in 2nd slot up from the bottom or 4th X16 slot from top(PCIEX16_4).which only has pins halfway as well. However, if you look at the Kitguru pic, there is no bent/sticking out pins as you can clearly see on your motherboard. Any way you could very carefully "pop" them into place with tweezers or something with a fine point?

drwoodcomb · Oct 31, 2014

1LiquidPC :

Hi,

Look at a picture..... lol, why didn't i think of that. I think the steam coming out of my ears was clouding my brain. I just looked at pictures and I see what you mean. That is so weird to me, i would have thought that for something to be 16X it would have to have pins run along the entire length of the slot. Anyways I'm pretty sure the bent pins are whats causing my problems. Unfortunately the pins are so long that you can't just bend them back in. In fact I think when they manufacture the motherboard the pins are sticking out and then they put the plastic cover over them. From what Im reading online, its not something I can do myself. The thing that really sucks is those bend pins scratched up the part of the video card that goes into the PCIe slot. Im really hoping its only cometic. Also Im not really sure how I could have done this myself. I feel like the board came like that? This has been the most problematic build Ive ever done! Thanks for your help!

1LiquidPC · Oct 31, 2014

Glad to help, at least in some way. I know what you mean with the frustration, can't think straight for something that would otherwise be obvious. I'm guessing your gonna have to get an RMA. I didn't notice any pin bends when assembling mine, but there's a good chance that might be your problem as they're not making proper contact. I doubt you could have caused it either, you'd have to install it wrong first, and rip it out some strange way that I can't even picture to do that. I'm pretty sure your cards will be ok even if the edge connectors(gold contacts) are srcratched a bit. I assemble circuit cards for a living and see this time to time. They can have scratches sometimes directly from the PCB manufacturer. They still pass in-house tests. As long as they're not "ripped up", they should be ok. I know what you mean with difficult build. I've been trying to get my OC stable for a month now. Thought I had it until the most recent UEFI update version 1004. After that update, the same setting I was using were no longer stable, so now I'm testing again/still,

Every other build I've OC'd before this one was pretty painless overall. Getting the voltages just right with X99/Haswell-E can be tricky...some google searches show that I'm not alone.

drwoodcomb · Nov 5, 2014

1LiquidPC :

Wooohooo! I finally have everything working as it should. Video card 1 is at 16x and video card 2 is at 8x. None of my friends care about computers and I had to tell somebody lol. By the way, I don't know if you have a Micro Center near where you live but I would recommend getting you components from there. You have to pay sales tax which kind of sucks but the good part is that they let me exchange my motherboard even though I had already owned it for more that 30 days! Also they sell CPUs there way cheaper than anywhere you'll find them on the internet. For example the i7-5820k is roughly $380 everywhere you look but Micro Center sells it for $300

As for you OC, I hope you figure it out. The new motherboard I exchanged had the oldest BIOS on it but to be honest everything is working great so Im scared to update. Maybe you could downgrade your BIOS to fix any issues you are having.

1LiquidPC · Nov 5, 2014

Nice! It was the motherboard then. Finally got it sorted...now to get to some gaming

I've apparently got a MicroCenter a few hours away (in Philly)..Maybe it's better not to be close with those prices, I'd be spending even more on upgrades, lol. I'd be like "with the money I saved here, i can buy..more parts!) Anyways. I've only had time to work on my X99 project on weekends, however I've had good luck last weekend and part of previous weekend. Actually set a voltage lower than in was with older UEFI for same OC. Working fine so far. I'm hoping around Thanksgiving or so to start swapping parts into my tower

Also, if your planning to stick with original UEFI, you may still want to read up on the article about the 1004. I wouldn't have updated myself from 0904 to 1004 if it weren't for what I'd read. Apparent it updates some low-level part of the firmware to correct a random voltage spike that can damage the voltage regulators on startup/shutdown. A quick web search should point to the article from LegitReviews. Just wanted to keep you informed. Also, any pics of the new build??

drwoodcomb · Nov 12, 2014

1LiquidPC :

I went ahead and updated the BIOS. Its weird but 1004 seems to cause issues with my USB ports not working sometimes when I reboot. Eitherway its a small price to pay if it will keep my voltages in check. Here is a picture of my build. Sorry it isn't a very clear picture. I love the case for that I got (NZXT H440) because its so minimalist and clean looking but the airflow really sucks. When I game I have to take the top and front cover off otherwise it gets a little toasty in there.

https://onedrive.live.com/redir?resid=C14549BE332BB5B%214582

Hopefully when you finish yours you can send me a pic.

1LiquidPC · Nov 12, 2014

Glad to hear from you again. Nice setup BTW

Super clean, plus I like the Black/White theme...same theme myself, hehe. Those twin Strix Cards look badass too. Didn't realize that particular case got that warm, but I guess were talking X99 and SLI crammed inside. Thinking of maybe changing it down the road for this reason? I imagine it would get old if you game frequently. Same thoughts here for 1004 UEFI, better to be safe than sorry. I haven't tried using USB ports other than keyboard/mouse. I hope I don't have problems there as I have a fair amount to plug in once I'm up and running. Also, here's a couple pics of my current setup if interested. Should be changing soon though

http://s47.photobucket.com/user/1LiquidPC/media/2013-11-22221615_zpsaf101fda.jpg.html

http://s47.photobucket.com/user/1LiquidPC/media/616b95a1-b06b-4a34-86c4-bbf9ce119746_zps68c56081.jpg.html

drwoodcomb · Nov 13, 2014

1LiquidPC :

Wow! That is an awesome looking build! I really want to watercool everything one of these days. It looks really good. I just haven't been able to find any water blocks for GTX 970. That and it cost so much to do. Thanks for sharing!

1LiquidPC · Nov 13, 2014

Thanks for the comments

Watercooling is great if your into it, but can get addicting, lol. Keep adding on. Also, not sure where you're located, but FrozenCPU and Performance-Pcs are now carrying 970 waterblocks. I ended up getting 2 670 blocks myself, which are supposed to fit the 970s just fine according to the manufacturer anyways. I was in a hurry and seen that the 670 blocks are compatible and jumped on them instead of waiting for the "official" 970 blocks, which are supposed to be the same, only change is changing the 6 to a 9. Plus I like the "sleeper" idea where it would look like I have 2 670s where in reality they're 970s. Your right about the crazy cost of parts for custom watercooling builds, probably because it's such a small market. I actually had my first WC setup back around 04, then switched to aircooling for a few years. What brought me back was playing Dragon's Age II with my new Radeon HD 6990 when I got it. I couldn't get it to stay under 90C even setting fan to run at 75% all the time, auto would spike to 95C....not to mention making the room sound like a 747 taking off, lol. Same card, game, settings, when I got it watercooled maxed out at 54C but averaged high 40s.

Platerpus7 · Jan 19, 2015

drwoodcomb :

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

Can I run two GTX 970 in SLI using 16X/8X PCI Gen 3.0

Reputable

Admirable

Titan

Honorable

Reputable

Admirable

Reputable

Splendid

Reputable

Splendid

Reputable

Splendid

Reputable

Splendid

Reputable

Splendid

Reputable

Splendid

Reputable

Splendid

Reputable

Splendid

Reputable

Splendid

Reputable

Share this page