5K and dual 4K displays on 15 rMBP 2016

Discussion in 'MacBook Pro' started by w0rd3r, Nov 19, 2016.

  1. w0rd3r macrumors regular

    w0rd3r

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    #1
    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!
     
  2. Brookzy macrumors 68040

    Brookzy

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    #2
    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". :) ]
     
  3. zhenya macrumors 603

    zhenya

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    #3
    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.
     
  4. Brookzy macrumors 68040

    Brookzy

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    #4
    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?
     
  5. w0rd3r thread starter macrumors regular

    w0rd3r

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    #5
    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.

    [​IMG]

    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:
    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
     
  6. zhenya macrumors 603

    zhenya

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    #6
    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.
     
  7. w0rd3r thread starter macrumors regular

    w0rd3r

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    #7
    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.
     
  8. Yoshimura macrumors regular

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    #8
    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.
     
  9. w0rd3r thread starter macrumors regular

    w0rd3r

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    #9
    Would you mean that a three 5K display setup would work with the rMBP closed ?
     
  10. Yoshimura macrumors regular

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    #10
    This, I don't know.
     
  11. JTToft macrumors 68040

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    #11
    - I doubt the GPU could handle all those pixels.
     
  12. Yoshimura macrumors regular

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    #12
    I should have specified that it is the discrete GPU that has 6. The iGPU only has 3.

    Since the 13" has only a iGPU, its options are more limited (one 5k or two 4k).

    More info here: Why Apple is using AMD GPUs
     
  13. Freyqq macrumors 68040

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    #13
    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.
     
  14. maratus, Nov 21, 2016
    Last edited: Nov 21, 2016

    maratus macrumors 6502a

    maratus

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    #14
    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.

    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
     
  15. jimthing macrumors 6502a

    jimthing

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    #15
  16. w0rd3r thread starter macrumors regular

    w0rd3r

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    #16
  17. jimthing macrumors 6502a

    jimthing

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    #17
    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.
     
  18. w0rd3r thread starter macrumors regular

    w0rd3r

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    #18
    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.
     
  19. Outrigger macrumors 68000

    Outrigger

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    #19
    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.
     
  20. w0rd3r thread starter macrumors regular

    w0rd3r

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    #20
    This is exactly why I said with the MacBook closed
     
  21. maratus macrumors 6502a

    maratus

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    #21
    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.
     
  22. w0rd3r thread starter macrumors regular

    w0rd3r

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    #22
    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
     
  23. maratus macrumors 6502a

    maratus

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    #23
    Why 3008 x 1692 and 3360 x 1890 instead of proper resolutions?
     
  24. w0rd3r thread starter macrumors regular

    w0rd3r

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    #24
    Because I'm using scaled resolutions
    Capture 2016-12-27 à 10.17.21.jpg
     
  25. maratus macrumors 6502a

    maratus

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    #25
    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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