Great write up! Learned some stuff myself here.
Here is my addition on cpus, and thunderbolt 4.
So before tiger lake and ice lake cpus, computer manufacturers would have to implement their own designs for incorporating a thunderbolt controller. This meant routing high speed differential pcie traces to an expensive controller. It also meant some effort of system integration to make it work with their design. This is what made it a premium feature with a premium price tag.
What sets tiger and ice lake apart is that the controller got integrated into the cpu dye. For ice lake, thunderbolt 3, and tiger lake thunderbolt 4. This brought down power consumption and improved some latency on the processing, which is a win win for everyone.
So tiger lake has a titan ridge thunderbolt controller on the cpu dye. This controller converts 4 lanes pcie3.0 to thunderbolt 4 at up to 4 ports. It is a shared bandwidth, so using all 4 will degrade performance across all devices.
On another note, frame work calls it usb4, which it is, but it is really thunderbolt 4. Thunderbolt 4 and usb 4 are not explicitly overlapping. I’ve heard more and more people say that usb4 is eGPU compatible. Well… not quite. It does call out pcie tunneling in the usb4 spec. I’m not sure if it’s their own implementation and we have yet to see silicon to make this happen or it’s borrowed from thunderbolt.
So these CPU’s make it so little effort is required to get thunderbolt out. A timing circuit and usb c controller that’s thunderbolt compatible is all that’s left. That’s why so many thunderbolt enabled laptops have surfaced.