1/13/2021, 12:30:14 PM









Note that there are many cases where the underlying PCI Express and DisplayPort traffic will not consume the full 40 Gbps Thunderbolt 3 interface. And in some of the configurations described, the amount of data and display together from these underlying protocols will consume more than 40 Gbps.

As a reminder, four lanes of PCI Express Gen 3 operate roughly at 32 Gbps (4 x 8 Gbps). Two links of (four-lane) DisplayPort 1.2 consume 2 x (4 x 5.4 Gbps) or 43.2 Gbps. For both these numbers, the underlying protocol uses some data to provide encoding overhead that is not carried over the Thunderbolt 3 link, which reduces the consumed bandwidth by roughly 20% (DisplayPort) or 5% (PCI Express Gen 3). Regardless, adding both together results in a figure above 40 Gbps.

If a consumer stresses a specific Thunderbolt port, and attempts to use dual, simultaneous displays at high resolution and additional PCI Express data, the Thunderbolt 3 silicon will prioritize the display traffic first and throttle the (PCI Express) data traffic. When each DisplayPort 1.2 link is established (via either a downstream Thunderbolt display, or via a downstream dongle to DisplayPort), the Thunderbolt silicon checks the maximum data rate that link can demand, and ensures there is enough Thunderbolt link bandwidth available.

For DisplayPort 1.2, the maximum bandwidth on the Thunderbolt interface is about 17 Gbps of data, so for a 20 Gbps Thunderbolt link, a single DisplayPort 1.2 interface can be used, and for a 40 Gbps Thunderbolt link, two DisplayPort interfaces can be connected (see Figure 7).

After the link is established, Thunderbolt transmits only the display traffic as demanded, so even though a DisplayPort 1.2 interface is used, if the screen resolution is set to 1080p, for example, only about 4 Gbps of the Thunderbolt link is used for display. If it is a 4K display, perhaps 14 Gbps will be consumed.

If a display is plugged in that exceeds the maximum number of displays available from the Thunderbolt silicon, the display is lit up, and the first display in the chain is deactivated. PCI Express traffic on the Thunderbolt interface is then allowed to consume the remainder of the link.



对比USB3.2 Gen2的20Gbps,似乎也没差多少……