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many upcoming Socket 1200 motherboards will support PCIe 4.0, but Intel encountered problems implementing the feature with the Comet Lake chipset, so Socket 1200 motherboards will only support PCIe 3.0 signaling rates when they come to market.

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We're told that some motherboards could still come to market with the PCIe 4.0-enabling components in the hopes that Intel will allow the next-gen Rocket Lake processors, which will drop into the same socket, to support the feature on motherboards with the chipset. However, given that Intel isn't known for allowing full backward compatibility with previous-gen chipsets, that's up in the air.