Dell P2715Q - 4k rez for Late 2012 iMac, MST = Secondary

Discussion in 'Mac Accessories' started by martinm0, Feb 23, 2015.

  1. martinm0, Feb 23, 2015
    Last edited: Feb 23, 2015

    martinm0 macrumors 6502a

    Joined:
    Feb 27, 2010
    #1
    Originally posted in Dell thread, but wanted to get this out to folks for opinions.

    Had an interesting discovery today messing around with the MST setting on the P2715Q. Neither of my computers officially support 4k resolutions (late 2012 iMac 3.4, 680MX, and Dell E6430 laptop work issued).

    The Dell laptop sits in a dock with DP, DVI and VGA out. I was hoping to use the DP out from the Dell monitor to my older Dell with DP in. Nothing happened when I set MST to Primary, so I flipped it over to Secondary setting and got an image on the Dell 27" monitor. To my surprise, it was a full 3840x2160 (monitor claimed 60Hz, but it was pretty choppy). Still, I didn't think the Intel GPU would do 4k (without MST I can only select 2560x1440 max).

    Hooked up the iMac and set MST to Secondary and BAM, 4k! Again, monitor claims 60Hz, but System Information shows 30Hz.

    Am I missing something about MST here? Is this a magic button for us with older macs that want 4k (albeit crippled)? It just doesn't make sense to me at all.

    EDIT: the Dell monitor is reporting 30Hz, not 60Hz. I was stupidly looking at the max settings, not the actual. Additionally, I hooked up my wife's Macbook Air w/ HD3000. It would not do 4k with MST set to Secondary, but it would to a HiDPI 1080p (no option for 2560x1440). When I turned off MST entirely, I could do 2560x1440.

    This is all really strange, yet very cool. The HiDPI options looks really, really good. The scaling on the iMac also looks great. Though, it seems the DP port provides a better image than the mDP port. Both support the MST setting (or both offer 4k when I set MST to Secondary), but there is some ghosting around text on the mDP. I don't recall the DP port having that and instead looks damn crisp.
     
  2. martinm0 thread starter macrumors 6502a

    Joined:
    Feb 27, 2010
    #2
    Bumping my own thread.

    Anyone able to explain my fndings? Or confirm the same results?
     

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