Connect Multiple Displays with One Cable (MST Support)

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Connect Multiple Displays with One Cable (MST Support)

I have been an Apple user for 20 years and only ever needed one external display. I now need a second external display. To my astonished disappointment, it appears macOS does not support connecting multiple displays *over a single cable* using the MST (multi-stream transfer) protocol. This means external USB-C/Thunderbolt hubs don't work. Daisy-chaining even the fanciest monitors in the world won't work. Sure, you'll see an image, but every monitor will show the same image. And this isn't something you can fix by turning off display mirroring. The ONLY way to effectively use multiple external monitors is to connect each of them directly to the computer. An enormously annoying pain in the neck.

To compound the frustration, I have learned that MST has been baked into the DisplayPort protocol that Apple claims to support for OVER A DECADE. Literally every modern Windows computer supports this functionality right out of the box.

And what's more--the Apple *hardware* DOES support MST! You can run Windows in BootCamp and daisy-chain or dock-connect multiple displays over a single cable all day long. So my beautiful, powerful MacBook Pro could do the job if Apple would just support MST. This is literally a software-only issue that Apple could fix with a couple lines of code in macOS.

I have researched a work-around to exhaustion and run into dead-end after dead-end. It even seems Apple has written macOS to specifically prohibit third-party display drivers that might offer a solution.

Apple is supposed to be the "IT JUST WORKS" brand. This should just work.

Apple, how--HOW--have you willfully ignored this otherwise universal display standard for so long? It seems like you just don't care. And after all the years of sticking up for the Apple ethos, it feels personal. You have to fix this. If you don't, the next laptop I buy will be a Windows. And I won't come back.

My question for the Apple community: for the love of God, have you found a solution to this?

Posted on Dec 15, 2022 09:28 AM

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Answer 1

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MRM615 Author

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Dec 15, 2022 09:56 AM in response to John Galt

Not helpful. That article only confirms the issue I described: multiple monitors must be connected directly to the computer. They cannot be daisy-chained together or connected via a hub.

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Answer 2

Dec 15, 2022 10:30 AM in response to MRM615

if you use a genuine ThunderBolt Dock, or your first display is a Thunderbolt Display, you can connect everything beyond that with whatever display protocols you wish for the rest of the chain.

The technical challenge is that these displays interfaces are switching very close to the physical limits of digital logic. You need an interface that can run at 40 G bits/sec AND reliably 'turn around' the inbound lanes and use them for outbound traffic to get enough bandwidth to support multiple large-sized displays.

Apple made the decision to support that only where it had a usable future (ThunderBolt) NOT where it would quickly hit the wall (USB-C) with no-longer-exotic 4K displays.

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The Apple standard for its built-in hardware-accelerated displays, makes them suitable for full-motion video for production/display of cinema-quality video with NO dropped frames, and NO dropouts or partial-blank scan lines due to memory under-runs or other issues.

The Windows standard is that you set the display resolution any way you like, and you live with whatever garbage or dropouts result.

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Answer 3

Dec 15, 2022 10:05 AM in response to MRM615

MacOS does indeed support daisy-chaining displays on models after about 2018.

The additional requirement is that the first connection must be via genuine ThunderBolt cable, and the first device (Dock or Display) must be a genuine ThunderBolt device.

In addition, to reach the required speeds and still maintain the Apple standard of display excellence, cables in such a setup are limited to 0.8 meters length, maximum.

MST over ordinary USB-C is NOT supported.

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Answer 4

MRM615 Author

Level 1

10 points

Dec 15, 2022 10:20 AM in response to Grant Bennet-Alder

Thanks for info. Do you have any suggested Thunderbolt displays? From what I see, Thunderbolt displays are *quite* expensive and far exceed my display-quality needs. Also, is it possible to use a Thunderbolt dock with HDMI or DisplayPort displays? Seems like that would require MST.

And WHY in the world isn't MST supported in the first place? It's technologically simple to do and compatible with existing Apple hardware.

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