Displayport MST support

Company purchased MacBook pro M2 and with multiple monitors the MAC is lagging behind Windows 11 in support of displays. Did Apple not think users would use multiple monitors with a Mac.


Please add MST so docks work without multiple monitors.

MacBook Pro 13″, macOS 10.15

Posted on Jun 21, 2023 8:10 AM

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17 replies

Jun 21, 2023 10:50 AM in response to Chkyerself

If you want to work on this issue:


Macs support multiple displays on one cable (out of the Mac) only when that cable is a genuine Thunderbolt cable, connecting to a first device that is a genuine Thunderbolt device (Dock Or Display)


ThunderBolt cables have twice as many data pathways as USB-C cables, and can momentarily 'turn around' the inbound pathways when needed for outbound data flows.

Jun 21, 2023 4:30 PM in response to Chkyerself

Apple states that the 13" M2 MacBook Pro supports only one external monitor. Your company could easily have checked that specification before purchasing that model.


The 14" and 16" M2 {Pro/Max} MacBook Pros can drive two (sometimes more) external monitors. I don't know if you can daisy-chain two monitors to a port operating in USB-C (DisplayPort Alt Mode). Daisy-chaining might be supported only for USB-C (Thunderbolt At Mode) monitors. The specifications should be more clear about this.

Jun 21, 2023 4:37 PM in response to Allan Jones

There are workarounds – like DisplayLink-equipped docks and adapters – that might let you attach more than one monitor to your 13" M2 MacBook Pro. These don't add hardware video outputs. They use third-party drivers to create virtual screens on your Mac, and to send out compressed updates to those displays to special decoding hardware in the dock or adapters. Not an ideal solution for playing high-end games, but it might be acceptable for many productivity applications.


https://www.synaptics.com/products/displaylink-graphics


Jun 21, 2023 4:56 PM in response to Chkyerself

Apple-Silicon 2020 M1 13-in MacBook Pro and Air and 2022 Apple-Silicon M2 13-in MacBook Pro and Air and the 2023 MacBook Air 15-in model are extremely-capable entry-level computers. They can support the internal display AND an External display up to the previously unheard of size of the Apple 6K display at billions of colors. But only ONE in addition to the internal display.


This may not match the way older computers forced you to work, since older computers were not able to support a really large external display. But it is NOT a defect. The spec was available long before you could purchase the computer.


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. This requires a hardware rasterizer/display-generator for each fully-accelerated display.


If you need more hardware-accelerated displays than the built-in and ONE external display, and an un-accelerated iPad if desired, you probably need a more capable computer.


If you are only doing program listings, spreadsheets, stock quotes and other slow to change data, there are some other solutions, but they require you to make some strong compromises.


Executive summary: More than ONE additional Hardware-accelerated display can NOT be added to the entry-level 13-in or 15-in M1 or M2 systems.

Jun 21, 2023 4:57 PM in response to Chkyerself

DisplayLink technology creates a "fake" display buffer in RAM, sends the data out over a slower interface to a stunt box with DisplayLink custom chips that put that data back onto a "legacy" interface. It is not a true "accelerated" display, and it can suffer from lagging. Just adding the DisplayLink Driver is not adequate to get a picture -- you need a DisplayLink "stunt-box" or a Dock that includes DisplayLink chips.


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It may be acceptable for a second display showing slow-to-change data such as computer program listings, stock quotes, or spreadsheets, but NOT for full motion Video, not for Video editing, and absolutely not for gaming. Mouse-tracking on that display can lag, and can make you feel queasy.


In a pinch, it may even play Internet videos (as one user put it) “without too many dropped frames".


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. This requires a hardware rasterizer/display-generator for each fully-accelerated display.


If you are only doing program listing and stock quotes and other slow to change data, there are some other solutions, but they require you to make some strong compromises.

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It is really nice to know that you can use a DisplayLink display if you MUST have an additional display for some of the types of data I mentioned. But that is NOT the same as the computer supporting a second, built-in, Hardware-accelerated display.


These displays depend on DisplayLink software, and are at the whim of Apple when they make MacOS changes. There have been cases where MacOS changes completely disabled DisplayLink software, and it took some time for them to recover.


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I think the Big Surprise for a lot of Hub/Dock buyers is that they thought they were getting a "real" display, but actually got a DisplayLink "fake" Display. If you got what you expected in every case, I would not use such pejorative terms to describe DisplayLink.

Oct 3, 2023 7:09 PM in response to cbondcarolina

caldigit dock is a Thunderbolt dock

Thunderbolt cable certified, with the Thunderbolt logo, and Under 0.8 meters for Apple brand, under 0.5 meters for brand X.


so yes, if that dock supports two displays at the resolution you want to run them, AND does not exceed the total thunderbolt cable bandwidth, you can get full motion Video on two displays. But that dock does not have ANY direct HDMI outputs, so you would also need adapters.


>> But NOT on the MacBook Pro 13-in or 15-in with Apple-Silicon, because those models supports only ONE external display with full-motion Video, regardless of what cables, adapters and docks are connected.


Note on the Caldigit web site for that dock: Original Apple M1 based computers can only support 1x external monitor through the Thunderbolt port.

Oct 4, 2023 12:50 AM in response to Servant of Cats

Servant of Cats wrote:

The 14" and 16" M2 {Pro/Max} MacBook Pros can drive two (sometimes more) external monitors. I don't know if you can daisy-chain two monitors to a port operating in USB-C (DisplayPort Alt Mode). Daisy-chaining might be supported only for USB-C (Thunderbolt At Mode) monitors. The specifications should be more clear about this.

I expected daisy chaining to work on my Macbook Pro M2Pro 14" through a Thunderbolt 4 cable, but unfortunately this does not work. My setup is as follows


Both monitors support daisy chaining through DisplayPort MST. First monitors comes with Thunderbolt 4 connection. As soon as I connect the second monitor through DisplayPort to the first monitor, the first monitor shows me that it wants to run at the same resolution and refresh rate (2560x1440@90Hz) as the second monitor. This means that OS-X seems only to support mirroring through MST which is IMHO completely useless.


Only way to get both monitors working properly is if I connect the first monitor through TB4 (which also charges my mac, and LAN) and the second monitor through the HDMI connector.


This means that generally the MacBook Pro 14" M2Pro model supports Dual Monitor support AND MST. But it seems to be a limitation in OS-X which prevents having two different screens running via MST. I hope Apple fixes this quickly because it's quite embarrassing that my Windows colleagues don't have this issues.

Oct 4, 2023 8:02 AM in response to AlexM_

<<. As soon as I connect the second monitor through DisplayPort to the first monitor, the first monitor shows me that it wants to run at the same resolution and refresh rate (2560x1440@90Hz) as the second monitor. This means that OS-X seems only to support mirroring through MST which is IMHO completely useless. >>


In general [√] Mirror Displays is a User-changeable SETTING on the Mac.



this pane shows [_] Mirror Displays turned OFF.

Oct 4, 2023 3:03 PM in response to AlexM_

Nether of the displays you posted is a genuine Thunderbolt Display.


the first display does appear to be a USB-C display, but Thunderbolt has twice as many data pathways, and when I say first device must be genuine ThunderBolt, USB-C is Not acceptable as the first display on multiple display cable on a Mac.


Windows may do things differently. You are welcome to switch back to Windows whenever you like.

Oct 5, 2023 1:41 AM in response to Grant Bennet-Alder

I'd love to understand your definition of genuine Thunderbolt Display.


FYI: The US page for the first display says

1 Thunderbolt™️ 4.0 (40Gbps signaling rate) with SuperSpeed USB Type-C®️ 5Gbps signaling rate (Up to 100W USB Power Delivery, Alt Mode DisplayPort™️ 1.4)

The 32" display is connected through the Thunderbolt cable, and it shows Ethernet networking via Thunderbolt. What does not work with my Macbook Pro 14" M2Pro is MST (Multi Stream Support) which works with Windows machines, and AFAIK even with 300 EUR Chromebooks.

Oct 5, 2023 5:19 AM in response to Chkyerself

A side note about USB-C (DisplayPort Alt Mode).


Dell's description of the 27" 4K U2723QE says (emphasis mine):


"Experience uncompromised picture quality by daisy chaining two 4K monitors. U2723QE is the world’s first 27" 4K monitor which allows daisy chaining of an additional 4K monitor at full resolution via USB-C—enabled by Display Stream Compression (DSC)."


https://www.dell.com/en-us/shop/dell-ultrasharp-27-4k-usb-c-hub-monitor-u2723qe/apd/210-bdpf/monitors-monitor-accessories


I doubt if Macs would support USB-C daisy-chaining with this monitor. But the statement is interesting, because it suggests that USB-C (DisplayPort) MST daisy-chaining of 4K displays has not been a thing on any computer – due to lack of bandwidth to do the daisy-chaining properly.


Oct 5, 2023 6:08 AM in response to Servant of Cats

Got ya.


I actually managed to get it working because thanks to your post I tried to find some more resources, including the docking station I ordered through my companies IT department a couple of weeks ago. I was quite frustrated because I didn't get it working. But today I found this Youtube video and this works now for me perfectly.


https://www.youtube.com/watch?v=0tvlSGlaQq8&t=211s


I connected the large screen via Thunderbolt pass through, and the other screen via DisplayPort (the one next to the HDMI port, but both were working, and the HDMI port would have worked too). Really happy now with the setup (see attached screenshots). All working through the one TB4 cable + LAN + USB Hub ...



Oct 5, 2023 7:36 AM in response to AlexM_

<<. I'd love to understand your definition of genuine Thunderbolt Display. >>


i am not fluent in German, and when I used the link your provided, I could not get the complete technical specs to appear.


When I entered "HP X 32K G3 Specs" in a web search, this US-english HP support page appears, and I was able to get their inscrutable specs page to appear. The devices is sold in the US as:

"HP Z32k G3 4K USB-C Display"


so it already looked bad for genuine Thunderbolt input.


Most display-makers list their input interfaces under a heading so that a reader can be sure this display features the ones the buyer wants Then there's HP.


A browser Find on that page does turn up the world "Thunderbolt". But only under 'cables included'. On all other issues the word does not appear.


Based on that manufacturer-provided evidence, I took it to mean this was a display whose input was USB-C, and NOT genuine ThunderBolt.


This is the US support page I was using to view that information, and come to those conclusions:


https://support.hp.com/us-en/product/product-specs/hp-z32k-g3-4k-usb-c-displays/model/2101244006


Based on that incomplete and misleading specification, a reasonable person could easily come to the same conclusion -- that this does not appear to be a Genuine Thunderbolt Display.


Displayport MST support

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