Can the iMac 5k support 2 external screens at 4k + 1440p?

Discussion in 'iMac' started by chmac7, Sep 18, 2015.

  1. chmac7 macrumors newbie

    Apr 17, 2013
    I have an iMac 5k. Currently I'm running 2 external screens, 1440p + 1080p. If I swap the 1080p screen for a 4k screen, will the iMac be able to drive all those pixels? I have the 4GB graphics card version if that makes any difference.

    My proposed setup would be:
    • iMac 5k at default resolution
    • 2560x1440 Dell U2713HM at full resolution
    • 3840x2060 new screen, probably scaled to "retina" 1440p
    Despite my searching I haven't found an answer so far...
  2. xmichaelp macrumors 68000


    Jul 10, 2012
    All those different screen sizes and resolutions would drive me crazy.

    As for the question.. most likely, I don't see why not. The 5k iMac can run a 5k Dell display so I don't see why it couldn't run a 4k and 1.5k. You only need one port for each.
  3. chmac7 thread starter macrumors newbie

    Apr 17, 2013
    Thanks, I guess you're right, it "most likely" can. :) Was hoping to hear of somebody who had successfully achieved it, but I hadn't seen the 5k Dell on the retina iMac. That gives me a lot more confidence that it'd work. Thanks.
  4. aliensporebomb macrumors 68000


    Jun 19, 2005
    Minneapolis, MN, USA, Urth
    I can tell you about my experience:

    I've got the iMac 5k i7 4 ghz model; I've got a 2650x1440 external 31" display and another 24" dell 1920x1024 LCD connected and they all work fine. I thought about getting a 4k external to replace the 31" but I'm still paying for the iMac so possibly later.
  5. chmac7 thread starter macrumors newbie

    Apr 17, 2013
    I have the same setup (with a 27" instead of 31"). One can never have too many pixels... :)
  6. chmac7 thread starter macrumors newbie

    Apr 17, 2013
    I borrowed a Samsung U28D590D 28 inch 4k monitor. Connecting this to my iMac Retina looks great. At the retina 2560x1440 resolution, the panel looks pretty good. The picture is a bit washed out, but it's a cheap panel.

    However, it is not possible to plug in an additional monitor. Digging into the apple docs, it seems like only MST (Multi Stream) 4k displays support one 4k plus a second monitor. This is stated here:

    It looks like MST is only supported on specific displays, and this Samsung is not one of them.

    At this point, it's not 100% clear to me whether the iMac would support any second monitor at 2560x1440 or if it will only support an Apple Thunderbolt Display as the 3rd screen. I'll post more if I'm able to run more experiments...
  7. ericv macrumors regular

    Mar 31, 2015
    I don't normally run this way, but I do have some monitors sitting around.

    I am able to run my iMac @ 5k, Asus PB287Q @ 4K/60hz, cheap samsung @ 1080P 60hz or 1600x90 60hz.

    Not your exact setup, but close.
  8. skyline r34 macrumors 6502

    skyline r34

    Oct 10, 2005
    San Diego
    Thinking about getting rid of my 2013 Mac Pro to get a few displays for my 5K iMac, can you connect two displays on one iMac to use it a triple display?All I need to get is a couple of display port cable's right? I want a few 5K displays from Dell but if i'm going to pay $2500 each I might as well get two more 5K iMac's and just use them as displays.
  9. ericv, Oct 4, 2015
    Last edited: Oct 4, 2015

    ericv macrumors regular

    Mar 31, 2015
    Yes you can hook up 2 displays to the iMac 5k. I've read somewhere that the iMac 5k cannot currently be used as a monitor. Might be old information, just be sure before you buy them.
  10. colodane macrumors 6502a


    Nov 11, 2012
    I'm sure you already know this, but there isn't a huge difference for most people between 5K and 4K displays. If you were to get two 4K Dell displays you would spend about $1000 total instead of the $5000 you are thinking about and have $4000 in your pocket plus make life easier for your GPU.

    You can already guess what I would do, but you may have some specialized need that can only be satisfied with three 5K displays?
  11. ericv macrumors regular

    Mar 31, 2015
    I agree. I have a 4K sitting right next to my 5k. Because they both output a scaled resolution to 2560x1440, everything is the same size. I cannot tell the difference between 4K and 5K.
  12. edjrwinnt macrumors member

    Mar 8, 2008
    North Ridgeville, Ohio
    My setup:

    iMac 5K i7 w/M290X
    Dell 28" LCD 4K on Thunderbolt 1
    Asus 24" LCD 1920 x 1200 on Thunderbolt 2

    I just cranked up the iMac itself and the Dell to the highest resolution and everything still works. I normally run both the Dell and iMac 5K at lower then their max resolutions. Once in a while when I go to wake up my machine the Asus shows no signal. I just recycle the power and comes back on. I'm running El Capitan and I also have two additional smaller LCD's hooked up via USB.
  13. panag macrumors newbie


    Oct 4, 2015

    What type of cable are you using to connect the Dell 4k;
  14. edjrwinnt macrumors member

    Mar 8, 2008
    North Ridgeville, Ohio
    Mini DisplayPort
  15. chmac7 thread starter macrumors newbie

    Apr 17, 2013
    Awesome. Thanks for the confirmation that it's possible, there is hope... :)

    @edjrwinnt Is your 28 dell the p2815q?

    @ericv & @edjrwinnt - Did you have to set the 4k display to MST?

    From my reading of Apple's support pages, it seems like it's only possible to use the second thunderbolt port for a monitor if the first is running on MST. The display I tested with doesn't support MST, so I wasn't able to verify, but using SST I could not connect an additional screen. I'm still running Yosemite though, so maybe El Capitane introduces some changes...

    Sadly I have to second the advice of @colodane and @ericv. The difference between retina 5k and half retina 4k is pretty minimal. If I'd realised that, I might now have a new MacBook Pro Retina 13 and 2 4k screens, for about the same price as my iMac. The only real gain from the iMac is that I have 24GB memory, and can upgrade to 32 if needs be...

    Thanks for all the replies folks, really appreciate it.
  16. Balckoutgr macrumors newbie

    Aug 9, 2014
    Can i use my Samsung U28d590 4K at retina mode (scaling to 2560x1440) using a mini display port to hdmi cable ?
    if yes, can i do the same with mac mini and macbook pro ?
  17. chmac7 thread starter macrumors newbie

    Apr 17, 2013
    I don't think the current version of HDMI can support 4k at 60Hz. I think you can only run it at 30Hz. Why not use a miniDP to DP cable though, the monitor and the laptop should support that better...
  18. Balckoutgr macrumors newbie

    Aug 9, 2014
    oh i see , even though the res is 2560x1440 or 1920x1080 retina mode we still need a display port conection for 60Hz..
  19. edjrwinnt macrumors member

    Mar 8, 2008
    North Ridgeville, Ohio
    Yes. Looked like crapped before on Windoze but actually works good on a good operating system.
  20. JeffyTheQuik macrumors 68020


    Aug 27, 2014
    Charleston, SC and Everett, WA

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