4K, 3840 x 2160 Resolution (UHD) at 60hz?

Discussion in 'MacBook' started by rogynskyy, Mar 17, 2015.

  1. rogynskyy macrumors newbie

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    Jul 9, 2008
    #1
    Hi,

    I'm thinking of buying the new macbook but the only reservation I have is whether it will work with my 28 inch 4K, 3840 x 2160 Resolution (UHD) Samsung screen.

    Apple website states:
    Intel HD Graphics 5300
    Dual display and video mirroring: Simultaneously supports full native resolution on the built-in display and up to 3840 by 2160 pixels on an external display, both at millions of colors

    However, they are not specifying whether that max resolution will be supported at 60hz or less.

    Any ideas?
     
  2. EnderTW macrumors 6502

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  3. JTToft, Mar 17, 2015
    Last edited: Mar 17, 2015

    JTToft macrumors 68040

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    #3
    - Perhaps the new MacBook is excluded from that article simply because it hasn't come out yet, and not because it doesn't support 60 Hz?

    EDIT:
    Actually, the MacBook specifications lists "Native DisplayPort 1.2 video output", and since DP 1.2 supports 4K @ 60 Hz, it's reasonable to expect that the MacBook will, too. Unless the iGPU puts some constraint on it, which might actually be the case (according to this article)

    There's another thread here about the issue. It seems it might be stuck at a lower rate because of the lack of active cooling.
     
  4. ctyrider macrumors 6502a

    ctyrider

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    #4
    There is no way it will support 4K at 60Hz, simply because there isn't enough bandwidth over USB3.1 gen-1 port. 5Gbps isn't enough to output 4K at 60Hz - matter of simple math.
     
  5. JTToft, Mar 17, 2015
    Last edited: Mar 17, 2015

    JTToft macrumors 68040

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    #5
    - The USB limitation doesn't apply. Apple has implemented native DisplayPort 1.2 which supports 17.28 Gbit/s.

    According to this VESA article, it will "support up to 4K (4096 x 2160) display resolutions at a 60Hz frame rate with up to 30-bit color."
     
  6. ctyrider macrumors 6502a

    ctyrider

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    #6
    Of course it does. USB 3.1 is the physical interface, which is used to carry DP output. It doesn't matter that DP 1.2 can support up to 17Gb/s - the physical USB 3.1 interface can only support up to 5Gb/s in aggregate output.

    http://www.apple.com/macbook/specs/

     
  7. JTToft macrumors 68040

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    #7
    - Please see the link I added to my post.
     
  8. zhenya macrumors 603

    zhenya

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    #8
    You need to consider that the usb spec allows for the bundling of data lanes for higher bandwidth resolutions. Specifically, they can bundle up to 4 of those lanes to transmit video, while leaving one lane dedicated for uninterrupted data transmission.

    http://www.anandtech.com/show/8558/displayport-alternate-mode-for-usb-typec-announced

    My guess is that the MacBook will be able to drive a single 4k display at 60hz.
     
  9. ctyrider macrumors 6502a

    ctyrider

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    #9
    That VESA article is referring to USB 3.1 gen-2 spec, which support full 10Gb/s lanes. MacBook will ship with gen-1 spec, which is only 5Gb/s lanes.

    Happy to be wrong on this one, but don't think it's enough for 4K/60Hz purely from bandwidth perspective. That's not even considering GPU and cooling issues that will be inherent to the CoreM.
     
  10. zhenya macrumors 603

    zhenya

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    #10
    On the tech specs page for the MacBook, they reference Displayport 1.2 which has a maximum resolution of 3840x2160 as part of the standard.

    Further, they state under the Video section: Dual display and video mirroring: Simultaneously supports full native resolution on the built-in display and up to 3840 by 2160 pixels on an external display, both at millions of colors
     
  11. iRun26.2, Mar 17, 2015
    Last edited: Mar 17, 2015

    iRun26.2 macrumors 68000

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    #11
    That would be very impressive!
     
  12. zhenya macrumors 603

    zhenya

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    #12
    I'll admit that they do not specify 60hz, even though that is what it should be if it's to spec. Displayport has certainly been a bit of a mixed bag in recent years though.
     
  13. iRun26.2 macrumors 68000

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    #13
    I think it is only 30Hz.
     
  14. ctyrider, Mar 17, 2015
    Last edited: Mar 17, 2015

    ctyrider macrumors 6502a

    ctyrider

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    #14
    The Apple's only official list of Macs that support 4K at 60Hz is this: https://support.apple.com/en-us/HT202856

    It does NOT list the new 12" rMB, while it lists 2015 rMBP (which came out at the same time). I would not bet a dime on 12" rMB supporting 4K at 60Hz (but again will be happy to be wrong).

    Another interesting datapoint - the newly released MacBook Airs' specs state maximum 2560 x 1600 external display support. That's despite them having more powerful U-series Broadwell, more powerful HD6000 GPU and 20Gb Thunderbolt-2.

    Explain to me how is it possible that rMB supports 4K/60Hz, while MBAs do not? I think someone at Apple went "marketing happy" when writing rMB spec page!
     
  15. JTToft macrumors 68040

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    #15
    - The Retina MacBook hasn't come out yet (it will on April 10). The 2015 13" Retina MacBook Pro has. Therefore they did not come out at the same time...

    I, too, doubt the rMB will support 4K/UHD at 60 Hz, but I'm not sure its not being included in the cited article proves that. It's quite conceivable that the article is only supposed to include currently available products.
     
  16. ctyrider macrumors 6502a

    ctyrider

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    #16
    Fair point. We will wait and see :)
     
  17. JTToft macrumors 68040

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    #17
    - Indeed. :)

    The 5300 graphics does support 60 Hz, but Intel recommends active cooling for that - which is where I'm guessing the limitation will lie. We'll most likely see 24 or 30 Hz, if you ask me.

    (I'm still rather certain that the DisplayPort output itself can handle 4K at 60 Hz, though.)
     
  18. PhillStew macrumors member

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    #18
    So since it does DP 1.2 what are the chances of being able to drive two external displays?
     
  19. EnderTW macrumors 6502

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    #19
    The 2015 Macbook Air with a non M processor doesn't support 4k at 60hz MST per the spec page. I'm not sure how the 2015 retina Macbook will be able to, unless I'm missing something.
     
  20. Nicky G macrumors 6502a

    Nicky G

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    #20
    I don't believe that's how USB Type-C works, and the ability for Apple to send out native DisplayPort is due to USB Type-C as the physical interface, not the USB 3.1 Gen 1 bus. If I understand USB alternate mode correctly, it uses the pins some of the USB 3.1 lanes would utilize if you're plugging in USB peripherals, but when using a DisplayPort device, it's native DisplayPort off the GPU, not "DisplayPort over the USB bus." I don't think the 5Gbps of the USB 3.1 Gen 1 bus applies at all to the bandwidth available to the DisplayPort signal coming off the USB Type-C interface in USB alternate mode.

    http://www.anandtech.com/show/8558/displayport-alternate-mode-for-usb-typec-announced

    However, 1) I could be wrong and 2) the GPU itself could well limit refresh rates of the external display.
     
  21. ctyrider macrumors 6502a

    ctyrider

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    #21
    I don't think you are wrong. However, DP 1.2 driving 4K display would take over all 4 lanes of USB-C, thus leaving no lanes for high-speed data.

    This basically means that if you drive 4K display over DP 1.2 - you won't be able to use high-speed USB devices. over the same port You should still be able to carry power and "slow" USB2 support over the same USB-C interface.

    This is going to change in the future when DP 1.3 over USB-C is introduced. DP 1.3 increases per-lane bandwidth, and can drive 4K via just 2 lanes, freeing up the remaining 2 lanes for high-speed USB 3.1 data.

    So in summary - I agree that USB-C gen-1 is not likely to be the limiting factor for 4K.. But GPU/cooling issues may well be. Time will tell.
     
  22. JTToft macrumors 68040

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    #22
  23. matt2053 macrumors 6502a

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    #23
    Im expecting this will only work if the 4k display is the only display (meaning the MB lid is closed). However there is currently no way to do 4k video out with the lid closed. Lid closed mode requires the MB to be on power source to do video out. And because of only one port, and the fact that Apple's adapter won't do DisplayPort out (only HDMI, over which 4k is NOT supported on the MB), it won't work.

    Hopefully soon we get an adapter with DisplayPort out.
     
  24. ctyrider macrumors 6502a

    ctyrider

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    #24
    Well, despite Apple's listing 4K/60Hz support for rMB - some early reports are to the contrary.

    From Ars Technica review:

     
  25. JTToft macrumors 68040

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    #25
    - That's actually not true. Apple has apparently updated the specifications for the adapter, now citing support for 4K at 30Hz.

    - That's just plain odd. And Ars even tested it on 10.10.3 (which supposedly brought the improvement)...

    I suppose your "we will wait and see" statement still holds.
     

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