In our Ryzen 7 3700X and Ryzen 9 3900X review , we made a startling discovery, that our ASUS ROG X470 Crosshair VII Hero motherboard was able to support PCIe 4.0 over the motherboard's primary M.2 slot. Yes, we got full PCIe 4.0 speeds on X470.Since then, a slide from ASUS has started to spread which showcases the levels of PCIe 4.0 support that's offered by the company's X470 motherboard lineup, with most motherboards supporting PCIe 4.0 over their motherboard's primary M.2 slot (which typically connects directly to the user's processor) while some others offer PCIe 4.0 speeds on the motherboard's primary PCIe 16x slot.As the table below shows, a majority of ASUS' B450 and X470 motherboard lineup supports PCIe 4.0 on their primary M.2 slot, with PCIe 4.0 being supported only when used with a Ryzen processor which supports PCIe 4.0 and when the motherboard uses a compatible BIOS file.