PCIE Gen 4 confusion

[Hofnaerrchen]

PCIe 4.0 is only present in X570 chipset in all the rest of Ryzen chipset motherboards are only PCIe 3.0 compatible, the problem is when the Ryzen 3000 (Zen 2) arrived to the market one of the upgrades from Zen 1 a Zen+ are integrated PCIe 4.0 support in the I/O die of the cpu, all A320, B350, X370, B450, X470 support this direct PCIe 4.0 lines from the CPU for the PCIe_1 16x but AMD needs to sell B550 and X570 motherboards and made and agesa update blocking this option to manufacturers, if you have the correct bios you can have a PCIe 4.0 support in your B450 motherboard

I think you forgot about B550. It also supports PCIe 4.0.

The reason - and it's one reason X670E/X670/B650E boards are much more expensive - you don't get/should not use PCIe 4.0 on 400 or 300 boards is signal quality. Higher bandwidth has higher requirements that older boards - even when enabled by the motherboard vendor - might not be able to reliably provide. In some rare cases it is even advisable to lower bandwidth in bios on PCIe 4.0 ready boards - for example when having problems with PCIe 4.0 GPUs. I doubt you want artifacting on your GPU or - even worse - write errors on your NVME SSD. Apart from that: The performance benefit of using PCIe 4.0 vs PCIe 3.0 is quite insignificant unless we start to talk about an RTX 4090 or professional storage usage - latter probably being less of a problem, because most desktop boards don't come with enough PCIe lanes to support a large number of said drives.

 

[Dr. Dro]

I had one of the gigabyte x370 boards with the beta BIOS for PCIE 4.0 but I never tried it. AMD should really unlock this now like they did with finally allowing the 5000 series on the oldest AM4 chipsets.

It's locked for a reason. The 300 and 400 series boards may not have the PCB quality for a stable signal, and even those that do have a high-end PCB may lack signal redriver chips that are compliant with the 4.0 standard. It's like using a 3.0 riser cable with a 4.0 GPU, it will be a mess.

You aren't missing out though. If you really feel like you need a PCIe generational upgrade you might as well just go with a Z790 or X670E board with Gen 5 at this point.

 

[BlaezaLite]

They wouldn't keep pcie gen 4 locked without a good reason, would they? Or am I just being a bit too trusting/naive? Getting a brand new Sapphire pulse 6800XT and it would be nice to see it at it's full potential. Although I don't have the best memory and a R 5 3600, so it's limited regardless, lol.

 

[Dr. Dro]

They wouldn't keep pcie gen 4 locked without a good reason, would they? Or am I just being a bit too trusting/naive? Getting a brand new Sapphire pulse 6800XT and it would be nice to see it at it's full potential. Although I don't have the best memory and a R 5 3600, so it's limited regardless, lol.

This one was for a good reason and done in good faith. The older boards may have signal redrivers and other miscellaneous ICs that aren't compatible with the 4.0 standard. Also due to way PCBs are "wired", the signal quality may or may not meet the 4.0 standards, which would just cause a malfunction if 4.0 support was enabled.

One of the chief reasons AM5 boards are expensive is the high price of the PCIe Gen 5 compatible PCBs. You may have noticed all of them are using several layers of copper and all. That would be why.

By the way do not worry about the 6800 XT being bottlenecked by a 3.0 x16 bus. It's nowhere near fast enough to cause a problem, and SAM/Resizable BAR will still work.

 

[AsRock]

Some B450/X470 boards are in theory PCIe 4.0 capable and there were some beta UEFI releases that were circulating that enabled PCIe 4.0 support. However, as not all boards could do PCIe 4.0, AMD decided that none of them would be allowed to do it, to reduce consumer confusion or to favour certain board makers/models.

Yes i remember some talk about it, i think GN went on about it some time ago. I believe there was a possible risk to so manufactures had to be sure of the longevity of running as before making it available.

EDIT:

https://www.amd.com/en/chipsets/b550

AMD finally brings PCI Express Gen 4.0 support on B550 chipset Motherboards

Now with the recent announcement of B550 motherboards, AMD is bringing "limited" PCIe 4.0 support to this affordable mainstream platform as well.

www.dsogaming.com