> So the NVMe card I added to an old motherboard’s PCI-E slot is really just PCI-E on PCI-E? Assuming that's a PCIe to M.2 adapter card, it's just rearranging

> So the NVMe card I added to an old motherboard’s PCI-E slot is really just PCI-E on PCI-E? Assuming that's a PCIe to M.2 adapter card, it's just rearranging the wires to a more compact connector. There's no nesting or layering of any protocols. Electrically, nothing changed about how the PCIe signals are carried (though M.2 lacks the 12V power supply), and either way you have NVMe commands encapsulated in PCIe packets (exactly analogous to how your network may have IP packets encapsulated in Ethernet frames).