Pre-Zen 2 AMD AM4 Motherboards Will Not Support PCIe 4.0

A couple of weeks ago, some AMD AM4 motherboard users began to notice that a new EFI option hinting at PCIe 4.0 support appeared. We couldn’t find the option on our installed AM4 board of choice, but after talking in private to a related vendor, we were told that the option would in fact work. As with most things of this nature though, there are some caveats.

At last week’s Computex, another vendor told us that PCIe 4.0 support would work on older motherboards, but only in the top slot. This would mean that the graphics card would have to relegate itself to another slot, which means it’d be running at less than x16, and could potentially impact gaming performance (there’d be a greater chance of this the higher-end the GPU is).

If you were hoping for PCIe 4.0 support on AM4, there’s some bad news to share. Over at reddit (via PC Perspective), AMD’s Robert Hallock makes it clear that mistakes were made, and that those mistakes will be corrected:

This is an error we are correcting. 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 news might come as a disappointment to some, but we’d have to imagine the number of people who actually planned to take proper advantage of a PCIe 4.0 slot would not hesitate to upgrade to the newer platform which officially supports it. Still, some attest that some vendors should have their own say as to whether or not an old board can do 4.0. As consumers, we can be thankful this isn’t actually a game-breaking decision.

At Computex, we talked to some vendors who were excited for PCIe 4.0, including GIGABYTE, which had a 4x NVMe SSD card on display, capable of pushing 15GB/s reads and writes over the 4.0 bus. That kind of prospect is exciting, but is again so high-end, that we wouldn’t expect many to opt for it and not upgrade their rig at the same point.

If you’re wondering how PCIe 4.0 would be possible on boards that existed before the actual spec was released to market, it’s simply because what’s in place can support the increased data, but as Hallock says, there’s no guarantee that the signaling will be ideal. It’s ultimately up to the CPU to enable 4.0 support, as well, so even if your older board would support it, you’d still need to upgrade the CPU.

AMD’s reasoning makes sense to us, but we still wouldn’t choose to push the option away. As we do with overclocking options already, users could simply be warned about incompatibilities. Ultimately, AMD feels it’s best to prevent any kind of nonsense entirely, and instead look forward to the actually officially supported platforms.

Curious about what kind of bandwidth PCIe 4.0 (and 5.0) will bring to the table? We posted a look at that a few months ago.