PCI-E 4.0 on older AM4 boards

[AWT]

Hi. I read that PCI-E 4.0 support was removed in one of the more recent BIOS updates for my motherboard, if a Ryzen 3xxx model is used (I'm still on an older BIOS version due to installation issues w/ newer versions).
Does that mean PCI-E 4.0 cards won't work at all if I decide to upgrade to Ryzen 3xxx, or will they work but only at 3.0 speed (which is to be expected on an X370 board, but makes no difference yet - only on future cards that may exceed the PCI-E 3.0 bandwith capacity).
I'm considering a future upgrade to a Ryzen 9 3950 (as this would make a worthwhile difference in performance compared to my current 1st Gen Ryzen 7), but since I'm receiving a PCI-E 4.0 card this week, it wouldn't make much sense to upgrade the CPU if I have to downgrade the GPU to get it to work.
Thanks in advance

[Bad 💀 Motha]

Nothing GPU wise even uses PCIE 4.0 yet as far as that much bandwidth.
RTX 30 and AMD RX 6000 series say PCIE 4.0 but they work fine on PCIE 3.0 as a single GPU from any of those series of models doesn't exceed the 3.0 bandwidth.

All Ryzen CPUs support PCIE 4.0 so IDK where you get this info from.

If you are staying on a Ryzen 3xxx series CPU, there is no need and you should not update to very latest BIOS because all of the very latest BIOS are ONLY for when you have a Ryzen 5xxx series CPU installed. It might actually hurt the performance of older CPUs

Now what a BIOS update might have done... and I'm spit-balling here. Is they may have made it so instead of some boards have a 4.0 vs 3.0 option. Which most of the boards do, it may have removed the 4.0 GPU options (nothing to do with NVME PCIE 4.0 btw) because this PCIE 4.0 option for GPUs caused many people to have issues when using certain GPU models. But again there is no reason to use the 4.0 option because no consumer single GPU even exceeds the 3.0 bandwidth and all the current GPUs are backwards compatible for PCIE 3.0 slot and/or setting.

[AWT]

Here's where I got the info from:
BIOS description from ASUS:
Version 7403
2019/08/23 10.22 MBytes
CROSSHAIR VI HERO BIOS 7403
1.Improve system performance.
2.Update AM4 Combo PI 1.0.0.3 Patch ABB
a.Fixes a compatibility issue with Destiny 2
b.Fixes an issue with certain Linux distros
c.Removes Gen 4 support when using Ryzen 3000 CPUs
3.Improves EZFlash performance to reduce boot time.

[nullable]

https://www.pcgamer.com/amd-has-decided-to-block-pcie-40-support-on-all-pre-x570-motherboards/

Seems like they intended for older boards to have PCI-E 4.0 support, but that implementation may not be guaranteed on older boards. So leave the option open and let users figure out if their boards can do it well enough or not. Or disable it for consistency. From a company/product perspective the latter is probably safer than explaining to thousands of individuals the situation if they happen to have an issue.

At any rate it seems like ASUS either decided to follow AMD's recommendation or believe its boards may not be fully PCI-E 4.0 compliant and better safe than sorry. After all, 99% compatible, or almost compatible, is just another way to say not compatible.

And it's not like you'd be pleased when you thought you could do PCI-E 4.0, and then discovered that it almost works... and ASUS never said or did anything about it.

[Bad 💀 Motha]

It won't matter either way. They probably did that change in the latest bios to rid some boards of the issues that can occur when using an RX 6000 or RTX 30 series gpu while the board is left set to PCIE 4.0 mode. Again these gpus work all the same at PCIE 3.0

See if they have a bios update that adds support for Ryzen 5000 series cpus, then look at getting maybe a 5600X or 5700X

[nullable]

Yes I would agree, that running those current cards in PCI-E 3.0 isn't an issue. A user may not prefer it emotionally, but practically they won't be disadvantaged or harmed. Performance should be the same in almost any instance.

[Ralf]

Dont let it bother you dude. People are running 6950xt in 2.0x4 slot and the performance if fine.

[AWT]

Just got a response from ASUS support.
"If you switch CPUs and use the Ryzen 3000 series, the PCIe 4.0 devices are compatible and also run at the desired PCIe 4.0 speeds.
The setting was simply removed from the bios, but not the function. The BIOS will automatically detect the PCie 4.0 Gen device and adjust it by itself."

[nullable]

Patch notes can be confusing. Support responses contradictory. It does raise some questions which one is right. If you're satisfied no need to fuss over it..

There's a part of me that might trust the BIOS update notes more than a rando support person. The support person probably isn't writing BIOSes. They might not be wrong, but I'd want some independent confirmation at this point if I was determined to be sure.

[AWT]

You're right. I will make sure I check again before I upgrade my CPU, for now I fortunately don't need to update yet. Will wait until I notice CPU bottlenecking in some game I play a lot, and/or find a cheap offer for a 3950X or 5xxx Ryzen 9.
I don't mind if the card I'm getting now won't run in PCIE 4.0 mode (fine with it running in 3.0 mode, as it doesn't exceed PCI 3.0 bandwith capacity anyway, and side-by-side comparison videos show the FPS difference is within margin of error), I just don't want the card to stop working if I put a Ryzen 9 3rd or latest Gen CPU into my system.

[Dr.Shadowds 🐉]

Here, see for yourself if need an example why PCIE 3.0 is still fine.

YouTube tester.
https://m.youtube.com/watch?v=dmGQP0RLjio

Expert hardware tester.
https://m.youtube.com/watch?v=0DKVVtirNM8

[Bad 💀 Motha]

Oprindeligt skrevet af AWT:

Just got a response from ASUS support.
"If you switch CPUs and use the Ryzen 3000 series, the PCIe 4.0 devices are compatible and also run at the desired PCIe 4.0 speeds.
The setting was simply removed from the bios, but not the function. The BIOS will automatically detect the PCie 4.0 Gen device and adjust it by itself."

Ok thanks for clarification because I have not heard anything like this from ASUS, MSI, Gigabyte or my distributors regarding any actual removal of the pcie 4.0 function. So yes my suspicion was correct, it just removes a toggle option in the bios settings is all.

[GOD RAYS ON ULTRA™]

That's good, might want to check with GPU z just to make sure.

[Bad 💀 Motha]

^ Yes that doesn't hurt either. It has a 3d test for a reason so you can see in real-time the PCIE speed change.