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> Does USB4 basically just add PCIe onto the USB bus? Yes. Which is kinda what Thunderbolt 3 does (except encapsulated in the TB packet format, not USB). The

> Does USB4 basically just add PCIe onto the USB bus? Yes. Which is kinda what Thunderbolt 3 does (except encapsulated in the TB packet format, not USB). The silicon world has been gradually converging on its Serializer-Deserializer/PHY technology. I don't know quite the family history, but I believe the PCIe PHY is very similar to USB3 which is identical to Thunderbolt 3. Since the link layer was the same, it was then "just" a matter of protocol design to make everything just use the same link. And that's how you got Thunderbolt 3 / USB 4.

tarheelredsox 7y ago
PCIe uses different rates than USB, but both at their basics use NRZ (Non-Return to Zero) https://en.wikipedia.org/wiki/Non-return-to-zero https://en.wikipedia.org/wiki/Non-return-to-zero. The bigger differences are in the channels they target. The channels characteristics drive the complexity of the signal processing circuitry required (eg Power and Cost) in the PHY devices. Hope that adds a bit of clarity to your PHY question.