Many PCs have a Thunderbolt 3 port that supports only one display. The LG UltraFine 5K and Apple Pro Display XDR 6K require a Thunderbolt 3 port that supports two displays to support 5K or 6K resolution. Apple refers to this as dual-link SST.
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Learn about the LG UltraFine 5K Display and how to use it with your Mac or iPad.
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It is the same as dual-cable displays.
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No, the 5K is already tiled. The Thunderbolt cable is carrying two single-link SST DisplayPort 1.2 signals like your dual cable display. You're asking the iMac Pro to power the 6K display with four tiles but the 6K display only has two DisplayPort inputs from the Thunderbolt cable. There is no reason that such a display having four tiles could not be made in the future but I don't know if the drivers in macOS or Windows can handle that. The tiling info is in the DisplayID part of the EDID. That info in the EDID is usually enough for Windows to work with the display. For some strange reason, macOS also requires an mtdd override file. There are several mtdd files for the Apple Pro Display XDR (6 different product IDs) - I don't know why there are 6 of them.
AMD graphics only supports 6 displays, so a tiled display requiring 4 inputs would leave only two DisplayPorts free.
What display is that? Does it do 4K 144Hz in macOS? I have an Asus XV273K display with similar dual cable mode but creating the mtdd override file in macOS is not enough to get it to work.
You are talking about dual-link DisplayPort over Thunderbolt which is two DisplayPort signals:
- single-link SST DisplayPort 1.2: 4K60Hz 10bpc
- dual-link SST DisplayPort 1.2: 5K60Hz 10bpc
- single-link SST DisplayPort 1.4: 5K60Hz 8bpc
- dual-link SST DisplayPort 1.4 (Titan Ridge Thunderbolt): 6K60Hz 10bpc
- dual-link SST DisplayPort 1.4 (not Thunderbolt): 8K60Hz 8bpc
A non-Thunderbolt host can convert two DisplayPort 1.4 signals to Thunderbolt 3 using a GC-TITAN RIDGE Thunderbolt 3 add-in card to support 6K on the XDR. No-one has tried it yet. It might not work if the XDR requires some special signal but people have done this with the LG UltraFine 5K.
Apple used AMD GPUs that support DisplayPort 1.4, but Apple connected the DisplayPort 1.4 outputs of the AMD GPU to Alpine Ridge Thunderbolt 3 controllers which cannot accept DisplayPort 1.4 signals (8.1 Gbps per lane). Alpine Ridge can only accept DisplayPort 1.2 signals (5.4 Gbps).
For 6K to work, you need a Titan Ridge Thunderbolt 3 controller at each end of the Thunderbolt chain. On the GPU end, the first Titan Ridge controller takes the two DisplayPort 1.4 signals and converts them to Thunderbolt. In the middle, Alpine Ridge and Titan Ridge Thunderbolt devices will pass along the Thunderbolt DisplayPort packets. At the end, the Titan Ridge Thunderbolt controller inside the XDR display converts the two Thunderbolt DisplayPort streams back to two DisplayPort 1.4 signals. A Thunderbolt controller has only one dedicated DisplayPort output. The downstream Thunderbolt port is used for the second DisplayPort output, so the XDR display cannot have a downstream Thunderbolt port to chain other devices (same as the LG UltraFine 5K display).
No, that display has fewer pixels than the LG UltraFine 5K.
There were two types of Target Display Mode hardware supported by the old iMacs: DisplayPort (2009, 2010) and Thunderbolt (2011-2014).
I don't know about the Target Display Mode hardware, but for TDM DisplayPort version to work on a 5K iMac, it would need to support two DisplayPort 1.2 inputs. Does a 5K iMac use two DisplayPort signals for it's internal displays? Output from the following command will tell how the display is connected (DisplayPort version, lanes, ports, EDID).
Code:
/System/Library/Extensions/AppleGraphicsControl.kext/Contents/MacOS/AGDCDiagnose -a > AGDCDiagnose_a.txt 2>&1
I don't think there's enough bandwidth for TDM Thunderbolt version. I believe TDM Thunderbolt version requires transmitting Framebuffer pixels using special Thunderbolt packets (like Thunderbolt Network connection). This may take some CPU cycles. Thunderbolt allows more bandwidth for DisplayPort than it does for other packet types so there probably is not enough bandwidth for 5K60Hz. Maybe 5K30Hz would work. I don't know if TDM Thunderbolt version required special hardware. I don't think so - I believe it could work like Sidecar (but without compression?).
The XDR has 5K and 6K tiled modes. The Dell only has an 8K tiled mode. You can't force it to accept a 5K tiled mode.
There is no difference between the links of the Dell 8K and the XDR except the links are transmitted over Thunderbolt 3 for the XDR. Actually, Thunderbolt 3 only has enough bandwidth for two DisplayPort 1.4 signals up to 6K. You can see the info for the links using the AGDCDiagnose command above.
The 2016 MacBook Pro uses Alpine Ridge and therefore is limited to DisplayPort 1.2 which is not enough for the 8K mode of the Dell 8K. Anyway, Apple's drivers won't allow DisplayPort 1.4 dual-link SST 8K60Hz on the Dell 8K display even though the display has been out for a long time. A DisplayPort 1.4 single-link 8K 30Hz mode works in macOS. The 60Hz mode works in Boot Camp proving that the problem is with the Apple drivers and not with the Apple hardware. I guess they want you to buy the 6K instead of the 8K.
Upload the file created by the AGDCDiagnose command (see above) so we can see how computer thinks the display is connected.
