3 display setups for a Mac and PC


I have 2 laptops I am trying to get to work with three 27" external monitors (I only use one computer at a time, no KVM switching). I purchased the TBT4-UDZ with hope and expectation of running 3 external monitors out from the TBT4-UDZ and having one TBT4 cable running out from the front of the TBT4-UDZ into a chosen laptop. I have not yet been successful.

The monitors:
1 Dell U2723QE - DisplayPort USB-C out of monitor to the DisplayPort port into TBT4-UDZ
1 HP Z27n G2 - DisplayPort plug out to DisplayPort port on
1 HP Z27n - only able to get it to work on Mac, via HDMI direct-connect

Windows Laptop:

  • HP Elitebook 840 G8 Notebook, running Windows 11 Biz with Intel Xe Iris graphics
  • 2 USB TBT 4 Type C with USB 4 support
  • 2 USB 3.2 Gen1 Type A ports (1 charging)
  • 1 HDMI 2 (4k)

Result: I can get the two display ports to work through TBT4-UDZ but cannot get a 3rd monitor to work - seems like no config works, even plugging 3rd monitor into direct HDMI port on laptop.

For the Mac laptop:

  • MBP M1 Max running Sonoma
  • 16" Retina built-in
  • 3 TBT 4 USB-C, all support charging, display port, TBT 4 (40G/s) and USB 4 (40G/s)
    Specs for display capabilities for this model:
    Up to 3 external displays with up to 6k/60hz AND one up to 4k/60 hz

Result: Unable to run all 3 through the TBT4-UDZ - I tried variations of 2 Display Port and one HDMI, but only the two Display Ports would work simultaneously.

I look forward to your wise counsel for getting a better outcome…

Ok, one minor breakthrough: after reading your (excellent) blog on downstream TBT4, it occurred to me that I was not using some of the downstream port functionality on the Dell.

I used a Displayport cable (both ends) to chain from Displayport out/downstream on the Dell to the Displayport in on the HP Z27n. For the PC, it is a victory. The control panel shows 4 independent screens. The negative is that the resolution it enables on the HP Z27n is only 1920/1080 and it looks like poor resolution. Only one (even lower res) option in this config… booo!

For the Mac, it seemed like it was going to work great, but what it did was create a child of the downstream HP Z27n that only mirrors the (parent) Dell upstream monitor (and port). It does not see 4 monitors, and when I highlight the Dell in the control panel it makes the edges of both the Dell and the HP Z27n go red. Thus, it’s really just a parent-child relationship. I can’t seem to get any other result. Booo…

This leads me to think I have to find a way to get a downstream signal from the TBT4-UDS, but the only remaining options seem to be data-only (and PD 7.5) from 1 USB C or 2 USB As. There is also the HDMIs, but I have not been able to get anything recognized from those when both Displayport outs are utilized.

Ok, I think I’ve come to understand some of the deeper details about multi-screen support if you want to drive > 2 extended screens:

1.) For Windows machines, you have to be really sure your compute device supports Multi-stream transport (MST). It also seems to mean you have to make sure at least one of your monitors has the ability to be daisy chained with downstream ports for display… correct?

2.) For Mac, the processor architecture matters, but Mac does not support Multi-stream Transport so you will NOT be able to drive 3 independent screens out of the TBT4-UDS. You would have to have more cables using other TBT ports on the Mac… correct?

For many people, adding an additional cable to your computer for a 3rd monitor is not a big deal, but for me it is. I want to be able to just change one cord (TBT4) and have 3 extended monitors running across whichever compute device I’m working on (Mac or PC). I think a lot of the depictions of the 4 screen capability of the TBT4-UDZ seem over zealous, and it resulted in me choosing the wrong dock. What’s most unfortunate is that it seems just the right dock WAS available:
UD-3900C4 (lower power tradeoff)
UD-ULTC4K (this looks like it might be a winner, but now I have to learn the tradeoffs of Alt Mode)

Maybe there is some config of the TBT4-UDZ I did not consider?

I am not a Plugable employee, just a fellow MBP M1 Max owner who has been experimenting with docking stations recently.

It is my understanding that:

  1. MBP Thunderbolt dock can support at most 2 monitors @ 4K. This is why you are unable to get 3 monitors with 1 TB4 connection from the dock to the MBP.

  2. The solution may be to get a USB-C docking station that supports DisplayLink as this may provide the solution you want noting i) DisplayLink does allow M1 MacBooks (i.e., as opposed to M1 Pro and M1 Max MacBooks) to support multiple displays even though the M1 MacBook does not and ii) I have not tried / used DisplayLink.

I hope this is helpful.

Thanks for replying…

Yes, I did kind of land on recognizing that each TBT4 port on the MBP can only provide 2 4k video outs, and this correlates to the two Groups on the TBT4-UDZ. However, I can also just have two TBT4 cables out of the mac then going into a UD-ULTC4K for 3 distinct channels of output, and likewise I can have two TBT cables going out of the PC and into a UD-ULTC4K. I would just tie the cables together because both Mac and PC have side-by-side TBT ports. It effectively creates a single cable (like) solution that is switchable from Mac to PC which then goes through the UD-ULTC4K. That results in what I’m really looking for which is 3 extended displays which can remember their positions and then I can map a bunch of apps to autoload into the same places each time. My work setup is… complex :wink:

Still, the UD-ULTC4K relies on ALT MODE which I know nothing about - especially nothing about how it works across Mac and PC platforms… would love to hear if anyone has experience before spending the money (again).

Thanks again for the reply-

Nope. I got that wrong. It could work, but there would need to be two input ports for the Mac/PC TBT4 cables on the docks, and there is only one.

An interesting problem created by Apple’s decision to only allow two video outs per port. I suspect I am an edge-case problem that would not make sense for Plugable to support with multi-in capability. Bummer.


Pleasure, let’s see whether I can shed some more light on this.

I can also just have two TBT4 cables out of the mac then going into a UD-ULTC4K for 3 distinct channels of output, and likewise I can have two TBT cables going out of the PC and into a UD-ULTC4K

I do not think this is correct as the UD-ULTC4K appears to only have 1 USB-C connection and that is to the host. I do not see where you can connect two TB cables (by the way, this is a USB-C dock, not a TB dock) from the dock to the MBP.

That results in what I’m really looking for which is 3 extended displays which can remember their positions and then I can map a bunch of apps to autoload into the same places each time.

I agree that this is doable with the UD-ULTC4K because it relies on DisplayLink which essentially has a chip in the dock which “generates” the additional displays. It should work!

DisplayLink has been around for a while and works on all platforms because it relies on the chip in the dock rather than the capabilities of the laptop / MacBook. I have never used DisplayLink but from the video on YouTube and elsewhere it seems extremely simple (i.e., connect the dock, install a driver and you are good to go)!

Personally, I would order one from Amazon and see whether it works. If yes then problem solved. If not then return it a no cost to you.

I hope this helps.

I will both agree / disagree with you.

The problem is not Apple allowing only two video displays per port. The problem is the 40Gbps limitation of Thunderbolt 3 / 4 (i.e., there is not enough bandwidth for more than 2 displays @ 4K). With the pending release of Thunderbolt 5 there is a real possibility it will accommodate 3+ monitors @ 4K (and fewer at 5K, 6K, etc.) as it is a bandwidth issue.

Thus, the solution is DIsplayPort because it provides additional capability built into the dock for those MacBook owners who need more than two external displays per Thunderbolt port!

Why not give DisplayPort a try, what do you have to lose? I see only upside for you!

Thanks for all of the feedback - it does seem you are right, Displaylink seems to be the winning solution for what I want to do. At least until there is a Mac available with TBT5+

Only downside seems to be (more) $

Good summary here:

Thanks again!

Happy it was helpful.

In terms of TBT5, it may not be the panacea you think because you would need i) TBT5 MacBook ii) TBT5 docking station and iii) DisplayPort/HDMI → TBT5 dongles as it is extremely unlikely that at TBT5 dock will have 3 DisplayPort / HDMI inputs.

There is no point considering / worrying about TBT5 until your docking station is TBT5 compatible, your MacBook is TBT5 compatible and all your monitors (except maybe 1) are TBT 3/4/5 compatible.

Your best bet is to go get a DisplayLink docking station which will do what you want.

Good luck (and please let me know how DisplayLink works out for you).

Apologies, the TBT5 reference was really tongue-in-cheek… I’ve worked in bigtech for decades.

I had an old dock that was supposedly Displaylink enabled, I tried it and it must be so out of date it doesn’t get recognized by the systems. However, I did spend some time perusing the user forums for Mac and seeing that there some major issues with Sonoma I am just going to hang back and live with my Mac having all 4 screens (HDMI) and the PC not. This seems to be the best way to get all of the performance out of all - compute, dock and screens. I will wait to see what the Plugable folks have to say about our agreed answer.

Many thanks!

One last thing.

The MBP will not recognize DisplayLink until you add the driver to macOS. You need to find the model number of the dock, download the correct DisplayLink driver (they are dock specific) and then try to use it. You will also need to adjust the Privacy / Screenshare settings to enable DisplayLink.

With that, fingers crossed that it works for you!


Thank you to ‘The206’ for posting, and to ‘JoelBC’ for adding to the discussion.

In regard to the issue at hand, the maximum number of displays possible when the TBT4-UDZ is connected to a Mac is two. It will not be possible to use three or four external displays when a Mac is connected to the TBT4-UDZ, and we do our best to call this out in our product listings.

If you require a docking station that will allow you to use three external displays with your Mac, then an alternative model docking station will be required.

‘The206’, may I ask you to please send an email to our direct support email address → support@plugable.com with ‘For ticket #- 431037’ in the subject line that contains the Amazon Order ID number for your TBT4-UDZ purchase?

For your reference, that information is typically available from here → https://amazon.com/orders

That information will help us to determine the next steps, as well as provide an alternative docking station model recommendation.

*** Please do not post the Amazon Order ID number here in our public forum (it contains personally identifiable information) ***

Thank you for giving us the chance to help!

Plugable Technologies

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