AMD's Ryzen 3000-series CPUs and X570 motherboards look set for an impressive and cohesive platform launch on July 7th, but some questions remain over backwards compatibility for older generations of Ryzen-based components going forward. Many have assumed that piecemeal upgrades which swap out motherboard or CPU will be fairly trivial, but realities are rarely that simple. We reached out to AMD, and they've brought us up to speed on how the AM4 legacy ecosystem is shaping up come the newest generation.
First up, and as we suspected, inter-operability between 1st generation and 3rd generation Ryzen components will be patchy at best. We reported in May that X570 motherboards would not likely support 1st Generation Ryzen CPUs, and that has been confirmed by AMD:
We do not anticipate 1st Gen Ryzen desktop processors will likely be paired with the AMD X570 chipset, and as such the fairly intensive validation efforts may not be done with many AMD X570 motherboards on this combination. Additionally, we wanted to note that AMD X570 is not replacing AMD X470 and AMD B450, it is coming as an additional offering, while X470 and B450 will still exist in the market to provide more options to consumers.
X370 and B350 motherboards meanwhile should, in the majority of cases, offer support for Ryzen 3000-series CPUs via a beta BIOS. However we have been told that these BIOSes also sunset support for 1st Gen. (2000-series) Ryzen APUs, making the upgrade process tricky for users with this combination of hardware. Realistically, it's probably best to upgrade both motherboard and CPU together unless you're confident with the update process and the components you have readily available should there be a hitch.
Generally speaking motherboards based on the A320 chipset will not support Ryzen 3000-series CPUs. There may be a few motherboard vendors hard at work engineering a solution but users should by no means assume any level of support.
That clears up backwards compatibility questions for 1st generation Ryzen platform components, but how about one of Zen 2's killer features, PCI-Express 4.0? Would X470 and B450 motherboards coupled to a Ryzen 3000-series CPU fully support the new high-speed standard, partially support it (i.e. to dGPU but not through the PCH), or not at all?
[..] Users today may find a PCIe® 4.0 option available in their pre-X570 motherboards. However, users should expect this option to be disabled when final retail BIOSes are released to implement full performance and stability for new 3rd Gen Ryzen™ processors. As pre-X570 motherboards were not designed with PCIe® 4.0 in mind, their designs may be incapable of running PCIe® 4.0 signaling with the requisite stability and performance. To ensure a reliable and consistent experience in the field, PCIe® 4.0 will not be an option ultimately available to pre-X570 motherboards. Users may continue with a beta BIOS if they desire, but performance and stability cannot be guaranteed.
It's our conclusion therefore that in effect PCI-Express 4.0 support through retail channels will be exclusive to X570 motherboards once the platform launches next month. That may continue unless and until B550 motherboards are released later on this year.
A retail X470/B450 motherboard shipped with UEFI BIOS that supports Ryzen 3000-series CPUs will not support the feature. Optional Beta BIOSes for PCI-Express 4.0 support on X470/B450 may be available from motherboard manufacturers but, even where it is, stability in this mode is not guaranteed as these 'boards have not been validated against the new standard. This doesn't technically contradict previous reports of PCI-Express 4.0 support on X470/B450 motherboard, but it's a factor X470/B450 owners should be aware of before upgrading to the new CPU generation. It also makes new X470/B450 motherboards bought today a significantly less compelling long-term purchase.
Of course, PCIe 4.0 will at launch be a very niche enthusiast-oriented feature (though much more widely exploited than PCIe 3.0 was at launch due to the prevalence of next-gen high-speed NVMe SSDs). It's hard to take AMD to task for what might have been misunderstandings based on incomplete information available just after Computex, but does necessitate a toning-down of some of the bombastic claims others have made with regards to wide-scale backwards compatibility thanks to platform continuity in the use of Socket AM4.