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PCI-E runs at x8 instead of x16

Hello,

I've recently updated BIOS to 0802 on ASUS Maximus X Hero (Wi-Fi AC) and GPU seems to have started running at "native x8 link speed." It used to always run PCI-E 3.0 @ x16, but now BIOS, GPU-Z and CPU-Z all show that it runs PCI-E 3.0 @ x8. Running GPU-Z render test or UNIGINE benchmarks doesn't help. It still shows PCI 3.0 @ x8. Clearing CMOS, reseating vid card didn't help. Running BIOS at optimized defaults didn't help. I'm running out of options here. Do you think I "broke" the mobo or vid card somehow or is it the BIOS issue. I hope it's the latter one. PC is only a month old and I had no issues with it until the recent BIOS update from 0505 to 0802. Here are my specs:

BIOS: 0802
OC'ed? No.
Motherboard: Asus ROG MAXIMUS X HERO (WI-FI AC)
CPU: Intel Core i7-8700K
AIO: Corsair H100i v2
RAM: Corsair Vengeance LPX 32GB (2 x 16GB) DDR4-3200
SSD: Samsung 850 EVO-Series 500GB 2.5"
NVMe (Boot): Samsung 960 PRO 512GB M.2-2280
NVMe (Games): Samsung 960 EVO 1TB M.2-2280
Graphics Card: Asus GeForce GTX 1080 Ti 11GB STRIX GAMING
PSU: EVGA SuperNOVA P2 850W

Thank you for your help!

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Have you tried going back to the previous BIOS version that worked?

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Have you tried going back to the previous BIOS? Did you update for a specific reason? If you don't need to fix something, it's often best to just leave the BIOS because stuff like this can pop up. 

 

It's not really an issue though, as PCIe 3.0 8x won't limit the performance of your GPU anyway. 

 

EDIT: Also, reinstall/update your GPU drivers too (do it first, so that if it does fix it, you don't have to change BIOS)

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1 minute ago, Legendarypoet said:

Have you tried going back to the previous BIOS version that worked?

Nope, I seem to have lost the 0505 file and it's not available on the ASUS site anymore. That was my next step, but I wasn't successful in locating the 0505 .cap file anywhere. Having said that, I don't think i've ever flashbacked BIOS before.

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2 minutes ago, knightslugger said:

check you PCIe lane options in the motherboard BIOS.

No possible. I can only choose between 4 options for top slot PCI-E: Auto, Gen1, Gen2 or Gen3.

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6 minutes ago, Oshino Shinobu said:

Have you tried going back to the previous BIOS? Did you update for a specific reason? If you don't need to fix something, it's often best to just leave the BIOS because stuff like this can pop up. 

 

It's not really an issue though, as PCIe 3.0 8x won't limit the performance of your GPU anyway. 

 

EDIT: Also, reinstall/update your GPU drivers too. 

I haven't tried going back, but that will probably be my next step as soon as i find the 0505 bios version somewhere. I've updated BIOS to lower the atrocious 1.429 V that psu was feeding the processor at stock speeds. After the update the temps never go higher than 60 deg.C and voltage never goes higher than 1.289 v.

 

I've deleted video drivers using DDU (Device Driver Uninstaller), reseated the card, but it still shows x8 link in BIOS, GPU-Z and CPU-Z.

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You can try contacting Raja@Asus on the ROG forums. He should be able to supply that version of the BIOS. I've seen him do it for other people (send older BIOS versions).

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1 minute ago, .fess said:

I haven't tried going back, but that will probably be my next step as soon as i find the 0505 bios version somewhere. I've updated BIOS to get lwer the attrocous 1.429 V that asus was feeding the processor at stock speeds. After the update the temps never go higher than 60 deg.C and voltage never goes higher than 1.289 v.

 

I've deleted video drivers using DDU (Device Driver Uninstaller), reseated the card, but it still shows x8 link in BIOS, GPU-Z and CPU-Z.

You could try moving the card to the other 16x slot, see how it works, then move it back. 

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Just now, Legendarypoet said:

You can try contacting Raja@Asus on the ROG forums. He should be able to supply that version of the BIOS. I've seen him do it for other people (send older BIOS versions).

That's awesome. Thanks Legendarypoet. I've seen his name floating around, so i'll definitely get in touch with him now.

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Just now, Oshino Shinobu said:

You could try moving the card to the other 16x slot, see how it works, then move it back. 

Does the second (bottom slot) provide x16 pci-e 3.0 speeds? I thought it was only capable of x8 link speeds.

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Just now, .fess said:

Does the second (bottom slot) provide x16 pci-e 3.0 speeds? I thought it was only capable of x8 link speeds.

Both should be capable of PCIe 3.0 16x on their own or 8x with two cards. 

 

From the board's specs:

 

Expansion Slots
Intel® Z370 Chipset
2 x PCIe 3.0 x16 (x16 or dual x8) 
1 x PCIe 3.0 x16 (x4 mode) *1
3 x PCIe 3.0/2.0 x1

 

I'll reiterate that there's no difference in performance with your card whether it runs in PCI 3.0 8x or 16x, the card can't fully saturate 3.0 8x

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3 minutes ago, .fess said:

Does the second (bottom slot) provide x16 pci-e 3.0 speeds? I thought it was only capable of x8 link speeds.

The very bottom slot is wired for x16 via x4 from the PCH so that will be slower.

Current Network Layout:

Current Build Log/PC:

Prior Build Log/PC:

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7 minutes ago, Oshino Shinobu said:

I'll reiterate that there's no difference in performance with your card whether it runs in PCI 3.0 8x or 16x, the card can't fully saturate 3.0 8x

That's good news. I really wasn't looking forward to disassembling the whole PC and sending for RMA. I'll try putting the video card in the bottom slot when i get home from work. Thanks Oshino!

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1 minute ago, .fess said:

That's good news. I really wasn't looking forward to disassembling the whole PC and sending for RMA. I'll try putting the video card in the bottom slot when i get home from work. Thanks Oshino!

No problem, hopefully it works. Even if it makes no difference to performance, things not running at the full capacity can be annoying xD

 

You could also try removing the GPU, uninstalling the drivers and running through a few things using the iGPU, then reinstall the GPU. If none of that works, reverting to an older BIOS, or just doing a new flash of the same BIOS is worth trying. 

 

Your board has USB BIOS Flashback, so you don't need to worry about messing it up. Honestly, wish every board came with the USB Flashback type feature (believe USB Flashback is Asus's name for it), considering without it, it's very possible to brick a board with a messed up BIOS flash. 

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I was also planning removing NVMe M.2 drives one by one and rebooting to see if that frees up some lanes even though I keep seeing that it shouldn't matter since CPU has 16 lanes for grpahics card and chipset provides 20 lanes for everything else, which total to 36 pci-e 3.0 lanes. I'm not sure how it works

 

Some people say that those 20 pci-e lanes are limited by DMI 3.0 which only runs at x4, effectively limiting the lanes to 20? Again, I have no idea idea what i'm talking about, so this too could be a wrong statement.

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Quick update, I installed the video in my old Z87K build and it also showed x8 speed. At that time I thought it's definitely the video card that's faulty, so I went back to the store and exchanged it for a new one. To my disappointment BIOS on both PCs still showed 1080 ti running at x8. I swapped the card for a gtx 760 and went back to x16 for that card, swapped it back to 1080 ti and it's x8 :( So I have no idea what's going on. I've done everything to troubleshoot and the problem's not fixed. maybe I'm just unlucky.

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  • 2 weeks later...

FINAL UPDATE: After all said and done, turns out the issue was with the motherboard itself. After exchanging the mobo for an identical one, the problem went away and GPU now runs at pci-e 3.0 x 16 with everything plugged in, including two M.2 drives.

Thank you everyone for your help.

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