One of the salient points of the next generation Ryzen 3000 CPUs coming next month was the support around PCIe 4.0. As the successor to PCIe 3.0, offering double the bandwidth and a range of other optimizations, the combination of the new technology paired with existing and new AM4 motherboards was always going to generate a bit of an issue with support. AMD, through a Reddit post, and confirmed by our sources at AMD’s partners, has clarified the issue.

Moving from PCIe 3.0 to PCIe 4.0 on a motherboard isn’t overly difficult. In order to qualify for PCIe 4.0 use, the signaling guidelines for the connecting traces between the CPU and PCIe slots have to be met. If the PCIe 3.0 motherboard was over-engineered in the first place, and supports PCIe 3.0 very well, there is every chance that those same connecting traces can carry a PCIe 4.0 signal without any issue. The problem becomes when some motherboards can succeed in PCIe 4.0, whereas others cannot because they can only barely support PCIe 3.0.

Before the launch of Ryzen 3000, many users (ourselves included) had speculated about PCIe 4.0 support on older motherboards, such as X470, X370, and the cheaper chipset variations. For those users who had bought into this market with a nice expensive motherboard, it was expected that these models were designed rigorously enough to also support PCIe 4.0. We have even seen some GIGABYTE motherboards already provide the option in the BIOS to support PCIe 4.0. However, AMD has nixed that idea, and those BIOS options will be reversed.

The only motherboards that will support PCIe 4.0 in the future will be the 500-series chipset, which is currently only the X570 range, although the B550 line-up is expected to come later this year. These chipsets are qualified for PCIe 4.0, but older chipsets will not be. AMD doesn’t want to create confusion in the market based on motherboard quality, where some users might be able to have it and others might not.

The exact quote comes from Robert Hallock, one of the Ryzen product managers at AMD, in a post on Reddit:

"Pre-X570 boards will not support PCIe Gen 4. There's no guarantee that older motherboards can reliably run the more stringent signaling requirements of Gen4, and we simply cannot have a mix of "yes, no, maybe" in the market for all the older motherboards. The potential for confusion is too high. When final BIOSes are released for 3rd Gen Ryzen (AGESA 1000+), Gen4 will not be an option anymore. We wish we could've enabled this backwards, but the risk is too great."

This means that in this instance, the recommendation becomes that if a user wants full access to PCIe 4.0, they will have to purchase an X570 motherboard. All Ryzen 3000 CPUs are likely to still run in X470 and X370 motherboards with a BIOS update, but because PCIe is backwards compatible, these CPUs will run in PCIe 3.0 mode.

To be honest, there are two ways to take this news. Sure, it’s a kick in the craw for anyone who invested in a high-end X370 or X470 motherboard. However the flip side of this is that there are not going to be many PCIe 4.0 devices on the market through 2019. We will see AMD’s Navi GPUs which are expected to replace the Polaris mid-range product stack, so if you already have a high-end GPU, it’s not going to bother you too much. For the PCIe 4.0 SSDs, we expect a couple of them to launch but these are the Phison E16 designs which run at 8W TDP and will likely command a high premium with an 8W TDP too – it might be best to wait until 2020 when dedicated PCIe 4.0 controllers come to the market.

I’ll be honest, it does make our job a bit easier. I contemplated having a news post where we kept track of all the 300-series and 400-series motherboards that support PCIe 4.0, but that suddenly got a lot simpler: if you want PCIe 4.0 on AMD in 2019, get a 500-series motherboard.

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Source: Reddit

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  • yankeeDDL - Monday, June 3, 2019 - link

    I have the MSI Tomahawk. It does support 105W CPUs (the 2700x, for example). The support page has not been updated yet (the BIOS is being updated now to the latest Agesa ComboPI) so I can't be 100% sure.
  • Topweasel - Monday, June 3, 2019 - link

    MSI has been very restrictive on devices that would be getting support for Ryzen 3k. The Tomahawk might be one of the better B350 boards. But I doubt you will see any support from MSI for Zen 2 on that. Specially not one like the 3900x (its not just a simple TDP number that impacts support). Overall considering how they have handled AMD products as a whole, I think they A.) Know they screwed up early and they either can not or would be to difficult to fix. B.) It's AMD related so they can't really be bothered.
  • Cooe - Monday, June 3, 2019 - link

    MSI has actually guaranteed support for their entire B350 line, so this just isn't true.
  • - Monday, June 3, 2019 - link

    Games fps leveled out after Gen3 x8 .. Several sites tested it. Maybe newer games on bigger hardware like 2x 2080's could benefit slightly, but i doubt it would make more than a sub 1fps difference. See more here or at Toms:
  • eva02langley - Monday, June 3, 2019 - link

    Basically, from the first impression we see with the chipset heatsink on x570, it means that PCIe 4.0 makes the chip run hotter.

    Basically, PCIe 4.0 could introduce risk of failling hardware. It would be totally irresponsible from AMD to go backward entirely. Yes, it kind of blow, but at least your mobo will not die because the hardware was not designed fot it.
  • nevcairiel - Monday, June 3, 2019 - link

    The chipset was always going to stay PCIe 3.0 anyway on older boards, it cannot magically grow a PCIe 4.0 controller - and thats what is running hot. The dedicated PCIe slots directly connected to the CPU without any intermediate chips where the only to even have a chance to support PCIe 4.0 on older boards.
  • cowboy44mag - Monday, June 3, 2019 - link

    I don't really see this as being a huge issue for a lot of people. I know that PCIe 4.0 will give much more bandwith to M.2 SSD devices, however most people were really hoping for a boost in GPU performance. That's not going to happen till at least 2020. The most powerful GPUs on the market don't support PCIe 4.0 because Nvidia chose to give the RTX chips a PCI-Express 3.0 x16 bus interface, even though the PCI-Express gen 4.0 specification was expected. AMD's new GPUs will take advantage of PCIe 4.0 however they are expected to only compete against the RTX 2060, RTX 2070, possibly the RTX 2080. That means that the very best gaming GPUs will still be the RTX 2080Ti and Titan, neither of which have native support for PCIe 4.0. By in large the most popular GPUs in use are the GTX 1000 series and they will of course have no native support either.

    By the time that AMD has a truly worthy high end GPU on PCIe 4.0 and Nvidia releases their next gen GPUs with PCIe 4.0 native support we will all be awaiting the release of X670 motherboards and Zen 2+. PCIe 4.0 in this generation is a "nice to have" feature but far from practical. As long as the 3000 series processors perform just as good on X470 as on X570 I see no reason to upgrade to X570 when the only real difference will be PCIe 4.0 support.
  • sing_electric - Monday, June 3, 2019 - link

    Totally agreed - PCIe 4.0 would have meant more on an SSD than on an x16 slot, and the layouts of most boards meant that adding PCIe 4 to the m2 slots of an older board was almost certainly out of the question. MAYBE for someone who wants to do GPU compute stuff, but if you're spending enough money to buy a Radeon Instinct (or something), the cost of a new motherboard is basically a rounding error in your build cost.
  • Ferro_Giconi - Monday, June 3, 2019 - link

    It won't matter anyway, even if a device is PCIe 4.0. Graphics cards already don't use the full bandwidth of 3.0, and anyone who is going to spend the money on a new CPU to get 4.0 and the money on a device that actually makes use of 4.0 speeds, a new $100 motherboard is going to be a drop in a hat compared to the CPU and 4.0 device that actually uses 4.0 speeds.
  • FreckledTrout - Monday, June 3, 2019 - link

    There are M.2. SSD's being shown off at computex already making use of PCIE 4.0 speeds. So it might matter to content developers or anyone where mex sequential IO throughput matters. For graphics cards its pointless at least today. I certainly will be skipping over this generation as long as x370 motherboards don't take any performance hit with Ryzen 3000 CPU's.

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