Thunderbolt 4 includes support for DisplayPort 2.0. How?

Those articles mention the possibility for a Thunderbolt 4 host to support 8K displays … but I don't believe that means that every Thunderbolt 4 host has to do so.

If you look at Apple's technical specifications, they talk about driving monitors with resolutions of up to 6K over Thunderbolt 4 / USB-C. Some of the Macs with higher-end M2 SoCs can drive an 8K monitor over HDMI (and I presume that involves some fairly recent revision to HDM).

I believe that for Thunderbolt 4 certification, a host has to be able to drive at least two monitors via TB / USB-C. That would explain why some Apple Silicon Macs have TB4 and others "only" have TB3.

Alexome wrote:

… but I don't believe that means that every Thunderbolt 4 host has to do so.

The specs do mention USB 4 over Thunderbolt 4!

https://discussions.apple.com/content/attachment/fd5d952a-d402-4757-894e-e97e9aa0c672

I'm referring to supporting 8K (or even higher-resolution) displays using DisplayPort 2.0. The specifications for USB4, Thunderbolt 4, and DisplayPort 2.0 might provide a way by which an implementation could do that – but that doesn't mean that every USB4 / Thunderbolt 4 implementation must support that.

I believe that a Mac mini M2 Pro connected with a "DisplayPort over USB-C" cable for example could support a 6K display with refresh rates above the 60 Hz stated by Apple. See comment 12 and Does DisplayPort Support 144Hz?.

Comment 12 – which isn't a statement by Apple – claims that the M2 Pro Mini will support refresh rates of up to 144 Hz over USB-C (DisplayPort). It does not claim that you can get the 144 Hz at 6K resolution. It may be that you can get 144 Hz for some lower resolutions, but not for 6K.

Yes, two 4 displays, in either of these setups:

one displays over Thunderbolt, and one over another Thunderbolt port

• one display over Thunderbolt, and one over HDMI

• Two displays over a Thunderbolt dock

One display over Thunderbolt / USB-C, and a second display over HDMI, isn't good enough for Thunderbolt 4 certification. That's what the M1 Mac Mini supports, and its Thunderbolt ports are TB3 ports.

The M2 Mac Mini has the same limit on the total number of monitors (two), but it's flexible enough to let both of those be Thunderbolt / USB-C monitors, and its TB ports are TB4 ports.

Can the Mac mini M2 act as a USB4 host? If the Mac mini (M1, 2020) supported it (listed here), the Mac mini M2 does too, I guess.

All of the Apple Silicon Macs have USB4 (Thunderbolt 3) or USB4 (Thunderbolt 4) ports. From what I read, the first batch of M1-based Macs were some of the first computers (maybe even the first computers) to offer USB4.

The question is, how do you engage USB4?

USB4 has some new USB data transfer modes. There are a couple of new "up to 20 Gbps" modes, one of which has a marketing name. There is a USB4 40 Gbps mode that's based in part on technology from Thunderbolt 3. I don't believe there are a lot of peripherals available yet that use these new USB transfer modes.

For a USB4 host, the USB4 "up to 20 Gbps" mode is mandatory, but the USB 3.2 Gen 2x2 "up to 20 Gbps" mode (which Macs apparently do not support) is optional.

For example, if I connect a Mac mini M2 Pro with a "DisplayPort over USB-C" cable to the DisplayPort port of a Dell display, how am I suppoed to know, whether this means DisplayPort over Thunderbolt or DisplayPort over USB4?

Unless the display requires Thunderbolt input, you're making the connection via USB-C (DisplayPort). There are only a handful of displays that require or accept Thunderbolt input, including

• The long-discontinued 27" Apple Thunderbolt DIsplay
• The 27" Apple 5K Studio Display
• The 32" Apple 6K Pro Display XDR
• The 24" LG 4K UltraFine and 27" LG 5K UltraFine Displays
• A 27" Samsung 5K monitor that came out recently
• One or two others that are the exception that proves the rule

Even before the DisplayPort 2.0 stuff came along, USB-C (DisplayPort) was enough to drive up to a 4K monitor.

If you are going through a Thunderbolt hub (like the OWC Thunderbolt hub) that has the ability to split a single TB chain into several, things might get a little more interesting. I believe that then, you might have

• A Thunderbolt connection, with two DisplayPort sessions inside, between the Mac and the Thunderbolt hub
• A USB-C (DisplayPort) connection to monitor #1 (resolution: 4K or less), on downstream TB port #1.
• A USB-C (DisplayPort) connection to monitor #2 (resolution: 4K or less), on downstream TB port #2.

This assumes that the Mac in question can drive at least two displays over Thunderbolt. Here I think we're talking about a way to parcel out native hardware outputs, as opposed to a workaround for adding DisplayLink-type ones.

Note that the M1 Mini can drive a display "with up to 6K resolution at 60 Hz" via Thunderbolt 3. My guess is that when Macs communicate with the 6K Pro Display XDR, they do this by using a pair of DisplayPort sessions within one physical Thunderbolt 3 connection. Each session carries data to refresh half the screen.

This would be consistent with the way that Macs handle 5K displays, and would explain why many Macs with TB3 ports are on the compatibility list for the Pro Display XDR.