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Reporters from tomshardware interviewed representatives of AMD for this purpose. They confirmed that 300 and 400 series AM4 motherboards can support PCI-E 4.0. AMD will not restrict this new feature to the new 500 series motherboards. The motherboard manufacturers are free to launch new BIOS support functions according to their own circumstances. After users refresh the BIOS, they can use the new generation of Revlon processing on the existing motherboards. It also has the latest PCI-E 4.0 slot.
According to the feedback from the motherboard manufacturers, they have successfully tested the support of PCI-E 4.0 on many 300 and 400 series motherboards, which can be enabled by simple BIOS updates. However, only the nearest PCI-E x16 slot to the CPU can be upgraded to PCI-E 4.0. The transmission speed theory can reach 64GB/s, but other slots still maintain the rate of PCI-E 3.0, including CPU. The M.2 interface provided, because the interface more than 6 inches away from the CPU requires updating the transponder and the timer.
But if you want to use a complete PCI-E 4.0, you still need to use 500 series chipsets. The new chipsets will provide PCI-E 4.0 support, not only PCI-E 2.0 now, which will help the motherboard to provide more high-speed M.2 interfaces.