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5K and dual 4K displays on 15 rMBP 2016

w0rd3r

w0rd3r

macrumors regular
Original poster
Jun 4, 2014
145
51
France
Hello everyone,
I'm not sure anyone would actually be able to test this before I do, but if at least the theory agrees with me I hope I'm good.

I want to use one 5K display (LG UltraFine) as well as 2 4K (3840*2160) displays with my 15" rMBP 2016.
If I understand everything correctly, I'll be able to do that without any issues. But I wanted to make sure before purchasing.

I looked for informations on Apple website without any luck unfortunately. The only thing they advertise is the ability to drive 2 5k or 4 4k displays. If anyone can confirm or infirm my thoughts, that'll be great. Thanks everyone!
 
My interpretation is that this is not possible. As you say, the tech specs say "or" and I think this is the key word. Up to two 5K display or up to four 4K displays. If it was possible to do what you want to they would have added "or one 5K display and up to two 4K displays".

In terms of the total number of pixels driven, your setup would have slightly fewer total pixels than the that of two 5K displays, because your 4K screens are actually UHD (lower resolution than "true" 4K). This makes me think that perhaps it is possible.

However calculating the pixels of a "true" one 5K, two 4K setup, it is more pixels overall than two 5K displays, and it is clear that two 5K displays is the limit.

In summary: two true 4K displays + one 5K display is definitely not possible because it would be more total pixels than the MBP can drive, and two UHD displays + one 5K is almost definitely not possible.

[Aside: Just sell the UHD displays and treat yourself to two 5K displays! Haha. Seriously though, mixing UHD and 5K will make for a bad experience because the scaling will be horribly off as not all the displays are the same DPI. See here for a representation - the UHD monitors are in the "bad zone". :) ]
 
I think you'll be fine because the 13" can drive 1 5k display OR two 4k displays. The way these machines are configured is that the 13" model has 1 Alpine Ridge daughter card for Thunderbolt 3, and the 15" has two of those cards. So each card is capable of driving 1 5k or 2 4k displays. On the 15" if you wanted two 5k displays, one would have to be plugged in to each side. For your setup, plug the 5k into one side, and the 2 4k displays into the other.
 
zhenya said:
I think you'll be fine because the 13" can drive 1 5k display OR two 4k displays. The way these machines are configured is that the 13" model has 1 Alpine Ridge daughter card for Thunderbolt 3, and the 15" has two of those cards. So each card is capable of driving 1 5k or 2 4k displays. On the 15" if you wanted two 5k displays, one would have to be plugged in to each side. For your setup, plug the 5k into one side, and the 2 4k displays into the other.
Click to expand...
If this works I would be astonished. Your reasoning is sound but if you had to plug each 5K into opposite sides surely Apple would have documented this somewhere?
 
Brookzy said:
My interpretation is that this is not possible. As you say, the tech specs say "or" and I think this is the key word. Up to two 5K display or up to four 4K displays. If it was possible to do what you want to they would have added "or one 5K display and up to two 4K displays".

In terms of the total number of pixels driven, your setup would have slightly fewer total pixels than the that of two 5K displays, because your 4K screens are actually UHD (lower resolution than "true" 4K). This makes me think that perhaps it is possible.

However calculating the pixels of a "true" one 5K, two 4K setup, it is more pixels overall than two 5K displays, and it is clear that two 5K displays is the limit.

In summary: two true 4K displays + one 5K display is definitely not possible because it would be more total pixels than the MBP can drive, and two UHD displays + one 5K is almost definitely not possible.

[Aside: Just sell the UHD displays and treat yourself to two 5K displays! Haha. Seriously though, mixing UHD and 5K will make for a bad experience because the scaling will be horribly off as not all the displays are the same DPI. See here for a representation - the UHD monitors are in the "bad zone". :) ]
Click to expand...

Alright, thank you for your answer, let me just talk to you about my setup+experience.
I used a 2013 Mac Pro with 2 4K Displays @60Hz. Apple said the only way I could use 3 was to plug the third via HDMI, so it'll work only @30Hz. I bought my third 4K display, and plugged it on a thunderbolt port via Mini DisplayPort. Worked like a charm @60Hz, not 30.

Setup-mi-2016-3.jpg


I sold my Mac Pro and now use a 5K iMac between 2 UHD Displays, so I'm quite aware of the difference between 5K and UHD (which is noticeable, totally agree with you on that). Thing is, I don't like having an even number of displays. I'd rather have a main one, so the 5K on this example, and 2 side ones I can put thing I want to see but not catching all my attention.

To go back on the topic, I am definitely positive it should work on a 2016 rMBP because it actually has 2 full Thunderbolt 3 drivers. Cf: The main difference between the two models is that the 15-inch MacBook Pro has two drivers.

That being said:
zhenya said:
I think you'll be fine because the 13" can drive 1 5k display OR two 4k displays. The way these machines are configured is that the 13" model has 1 Alpine Ridge daughter card for Thunderbolt 3, and the 15" has two of those cards. So each card is capable of driving 1 5k or 2 4k displays. On the 15" if you wanted two 5k displays, one would have to be plugged in to each side. For your setup, plug the 5k into one side, and the 2 4k displays into the other.]
Click to expand...
This is exactly my understanding. One driver will push the pixels to the 5K display, and the other one will take care of the 2 UHD ones.

TL;DR: I can't see why Apple would say 'up to two 5K and 4 4K displays' and 1 5K + 2 4K won't work. As far as graphics goes, I guess one 5K is ± the same as 2 4K.

Thanks again for your insights guys.

Bob
 
Brookzy said:
If this works I would be astonished. Your reasoning is sound but if you had to plug each 5K into opposite sides surely Apple would have documented this somewhere?
Click to expand...

Yeah, we will see, but we already know that in certain situations the ports have differing capabilities. My previous post needs a bit of an edit because it's actually just the 13" non-TB model with just 1 Alpine Ridge card. The 13" TB models also have 2 Alpine Ridge cards but because of the number of PCI-Express lanes available on the CPU full bandwidth is only available through the card on the left. I'll be generous and say that sometimes in Apple's quest to leave spec sheets simple, they don't always paint a full picture. But they usually have excellent supporting documentation.
 
Alright guys, got an official answer from Apple.
As zhenya said, this is totally doable.

One 5K and 2 4K displays is supported for the 15 inches MacBook Pro, making me a happy man. Thangs again for all the answers, and I'll report in a few weeks when I got everything set up to let you know all is good.
 
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GPU has 6 DisplayPort connections. Each display need one cexcept for 5k displays that needs 2.

So maximum of 5k displays is two. (2 x 2 for the external displays + one for the build-in display).
Maximum of 4k displays is four because there are only 4 USB-C port.

But you could also do two 5k and one 4k or one 5k and three 4k.
 
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Yoshimura said:
GPU has 6 DisplayPort connections. Each display need one cexcept for 5k displays that needs 2.

So maximum of 5k displays is two. (2 x 2 for the external displays + one for the build-in display).
Maximum of 4k displays is four because there are only 4 USB-C port.

But you could also do two 5k and one 4k or one 5k and three 4k.
Click to expand...
Would you mean that a three 5K display setup would work with the rMBP closed ?
 
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technically this should work, as long as you put 2 4k on one side and 1 5k on the other side. Each side (thunderbolt controller) has just enough bandwidth for this.
 
Yes, it's possible. Each TB3 port supports up to 1x 5K or 2x 4K daisy chained or separately connected. Each TB3 controller also supports up to 1x 5K or 2x 4K screens (I need to double check this limitation)

One 5K monitor is treated by dGPU like two screens.

One 4K monitor is treated by dGPU like one screen.

Built-in display is treated like one screen as well.

The maximum number of separate screens connected to dGPU is 6.

The maximum number of 4K screens connected to dGPU is 4 + built-in. The maximum number of 5K screens connected to dGPU is 2x + built-in.

Freyqq said:
technically this should work, as long as you put 2 4k on one side and 1 5k on the other side. Each side (thunderbolt controller) has just enough bandwidth for this.
Click to expand...

AFAIK you may be able to connect 2x 5K screens and 4x 4K screens to one side..... There's enough bandwidth for that from one Alpine Ridge controller, but...... although you definitely have 2x DP1.2 streams from a single TB3 port (otherwise 5K would be impossible) and that's enough to drive two 4K in daisy chain..... It may be impossible to use the second port for DP1.2 at all if two streams are taken by the first port if only 2x DP1.2 links are going from dGPU to each Alpine Ridge controller. But I couldn't find any information that states this explicitly. It appears that Ap
 
Last edited:
w0rd3r said:
No way, those ports output data only, not video.
Click to expand...
You say that, but who knows for sure though?
With no full specs listed anywhere yet (camera resolution unknown, for example), and no one in possession of the LG 5K to actually try it, it's all speculation at this stage.
 
jimthing said:
You say that, but who knows for sure though?
With no full specs listed anywhere yet (camera resolution unknown, for example), and no one in possession of the LG 5K to actually try it, it's all speculation at this stage.
Click to expand...
Fair enough. The dGPU will treat the 5K display as a 2 screens, thus maxing out the capabilities of the port. Therefore, I can't see how you'll be able to output to another display. As far as I understand it, the USB-C out ports are data only.

But you're right, none of that has been verified yet.
 
w0rd3r said:
Would you mean that a three 5K display setup would work with the rMBP closed ?
Click to expand...

No, this would not work. the max number of 5K is 2. each 5k is taking 2 x 1.2 dp and the 15" only supports a total of 6 including its own.
 
w0rd3r said:
This is exactly why I said with the MacBook closed
Click to expand...
You can't because there're only two streams of DP1.2 routed to each Alpine Ridge TB3 controller. When you close the lid, the DP1.2 for built-in display is just left unused. Another (sixth) DP1.2 stream isn't used at all.

To maximize the capabilities of Pro 450/455/460 you'd need three AR controllers with 3x (single port) or 6x (dual port) TB3 ports in total instead of two AR controllers with 4x (dual port) like now.
 
Alright, here I'm back with the setup I wanted from the beginning.
15" 2016 MacBook Pro with :
LG 5K UltraFine + 2 x LG UHD 27UD88-W

36 518 400 pixels.

Just 3 USB-C cables, and the MacBook both has power and video.
Behind the 5K display I plugged in a USB-C to ethernet+USB adapter, works like a charm, got ethernet, wired keyboard as well as a USB hub, all this from a single cable.
Everything works @60Hz of course.
5K MacBook Pro.jpg


Here is a pic as well as the system report for you guys. Feel free to ask me anything, and if this can help anyone figuring out how the 2016 MacBook can handle pixels, that's perfect.
system report.jpg
 
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w0rd3r said:
Alright, here I'm back with the setup I wanted from the beginning.
15" 2016 MacBook Pro with :
LG 5K UltraFine + 2 x LG UHD 27UD88-W

36 518 400 pixels.

Just 3 USB-C cables, and the MacBook both has power and video.
Behind the 5K display I plugged in a USB-C to ethernet+USB adapter, works like a charm, got ethernet, wired keyboard as well as a USB hub, all this from a single cable.
Everything works @60Hz of course.
View attachment 680180

Here is a pic as well as the system report for you guys. Feel free to ask me anything, and if this can help anyone figuring out how the 2016 MacBook can handle pixels, that's perfect.
View attachment 680179
Click to expand...
Why 3008 x 1692 and 3360 x 1890 instead of proper resolutions?
 
w0rd3r said:
Because I'm using scaled resolutions
View attachment 680181
Click to expand...
If scaling is affecting this, then it's not a HiDPI scaling but just a different resolution. Your screens physically aren't running at full resolution. You can try and change the scaling and double check this (I may be wrong of course)

Also, if you want full 5K resolution, you can't connect any other screen to the same side (same controller). You need 5K on one side, and two 4Ks on the other side.

Also, I don't understand why two USB cables go into the hub and two USB cables are going from the hub to displays. It doesn't make any sense.
 
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