Quote from: xpclient on January 25, 2021, 18:39:20
Ah that is very useful, interesting, important and rare info that clears my confusion. Thank you for explaining the differences between DisplayPort in TB and in USB-C Alternate Mode.
Wikipedia does mention this too but in the USB-C article: "All Thunderbolt 3 controllers both support Thunderbolt Alternate Mode and DisplayPort Alternate Mode. Because Thunderbolt can encapsulate DisplayPort data, every Thunderbolt controller can either output DisplayPort signals directly over DisplayPort Alternative Mode or encapsulated within Thunderbolt in Thunderbolt Alternate Mode. Low cost peripherals mostly connect via DisplayPort Alternate Mode while some docking stations tunnel DisplayPort over Thunderbolt."
So a Thunderbolt 3 SSD like Samsung X5 which is connected to an x4 PCIe link TB3 port in my high-end gaming laptop will probably not see any further improved performance for a TB4 port?
I would like to add that USB4 also supports tunneling. You can tunnel simultaneously USB 3.2 and DP 1.4a irrespective of Thunderbolt support (TB support adds PCIe tunneling and is optional).
Alternate modes really relate to the port itself - USB-C. They essentially dictate how it's wired up, what the pins do. In DP mode, the port becomes a weirdly shaped DP. All the high-speed serial lanes of USB-C port will be video out (at least in the case of 2.0; but in all cases, the port will be DP-only) and it should behave like a DP on a GPU. In a TB mode, half the links are used for receiving like it's with USB (you've got 40+40 instead of 80+0), you've got full-duplex communication and it should behave like a TB port. TB itself does support carriage of DP. Because TB was designed to offer an all-in-one solution (power + data + video) so that you can have just one cable for everything. And now, as I already wrote, USB4 joins the fun with TB-like DP tunneling. You can imagine it like switching between GPU, TB controller, USB controller. In reality, there should be just one controller behind the port (either USB or TB) which is connected to all the different "resources" and which does the switching internally (it's responsible for the detection, negotiation and reconfiguration).
Actually, SSD permitting, you should see an improvement in write speeds. As long as there is no high resolution or very high refresh rate display daisy chained on the same port (3840x2160 @ 60 Hz with 24 bit colour depth takes, I believe, almost 13 Gb/s). Exactly because of the change in how much bandwidth is reserved for DP. I believe TB3 reserves 18 Gb/s for DP - insane if you ask me. Leaving at most 22 Gb/s for data, even with four links of PCIe. In TB4, you get the full 32 Gb/s. I believe this is the main reason why you see a significant improvement with eGPUs. In this respect, I have poorly worded my previous post. In the cut-down x2 implementations, you've got so much headroom that the DP reservation doesn't bother you. But in the full x4 implementations, you only really get x2.75 because of the reservation. As I wrote, the difference is small in mixed scenarios, at least with higher resolutions (see above). And even in data-only, it's fairly specific - like eGPU, like really fast SSDs. And of course, it's easier to hit the limit if you daisy chain.