Help me understand 6 TB ports vs. 3 possible 4k displays, etc.

Discussion in 'Mac Pro' started by gjarold, Jun 10, 2013.

  1. gjarold macrumors regular

    Nov 14, 2007
    Can someone explain how monitor connections work ?

    Background: my 2009 mac pro has 3x gt120 cards, and I have six displays running off of it. Easy.

    With this system, I see that there are six thunderbolt ports, so ... I could attach six displays there, right ?

    BUT, every mention of the graphics cards says "up to three 4k displays" ...

    What does that mean ? Does that mean that a 4k display requires two TB connections ?

    And if that is the case, doesn't that mean if I attach three primary displays at 4k, all I have left is the HDMI port, and then that's it - only four displays ?


    EDIT: OH, and also, if 4k displays take up 2x TB, and since three displays is a very common setup, then you don't have any more TB ports, right ? So you have to choose between triple monitors or fast disk connection ?
  2. JesperA macrumors 6502a

    Feb 10, 2012
    why would you think that a 4k monitor would use 2 tb ports? it will obviously just use one tb connection.
  3. Nermal Moderator


    Staff Member

    Dec 7, 2002
    New Zealand
    That's not obvious at all; if there are six ports and the specs say that you can connect three displays then it's completely logical to think that each display uses two ports.
  4. gjarold thread starter macrumors regular

    Nov 14, 2007
    I have no idea, actually. So a 4k display can be driven by one TB port ?

    But then what explains the "up to 3" 4k displays ? Since there are two cards, you'd think that number would be divisible by 2, right ? Either 2 4k displays or 4 4k displays ?

    So that's the two questions:

    1. where does "up to 3" limitation come from

    2. If I plug in 3 4k displays, can I also drive 3 more regular displays ?
  5. dukebound85 macrumors P6


    Jul 17, 2005
    5045 feet above sea level
    I would wager the limitation lies not with TB, but with the output that can be handled by the GPUs
  6. gjarold thread starter macrumors regular

    Nov 14, 2007
    Ok, fair enough, but then wouldn't it be divisible by 2, since there are two cards ?
  7. JesperA macrumors 6502a

    Feb 10, 2012
    Yes, and there was 4 USB ports to so every usb peripheral need to use 2 usb ports tol with your logic? Current 4k displays from Asus and Sharp only need 1 displayport connection.
  8. Yahooligan macrumors 6502a


    Aug 7, 2011
    Unless you read what Intel posted...

    A single TB2.0 port can drive a 4k display, you don't need two TB2.0 ports to drive a single 4k display.
  9. azentropy macrumors 68020


    Jul 19, 2002
    I'm pretty sure I heard 3 TB controllers in the keynote.
  10. gjarold thread starter macrumors regular

    Nov 14, 2007
    Oh, ok - so there are 6 ports, but 3 controllers.

    So what happens if I plug in 3 4k displays, and 3 more lower res (2560x1600) displays ?
  11. tuna macrumors 6502

    Apr 11, 2010
    I think you guys are overcomplicating it. 3x 4K resolution displays is just one maximum video output profile, there will probably be others for when you don't need three 4K displays. For example, I remember back when I used to shop for graphics cards, the maximum output for a graphics card might have been listed as "1x 2560x1600 and 1x 1280x800 OR 2x 1920x1200". If you wanted to power

    In this case, one maximum will be 3x 4K displays, but another maximum might end up being "2x 4K displays and 2x 2560x1600 displays".
  12. ender78 macrumors 6502

    Jan 9, 2005
    It takes a lot of horsepower to drive 4K displays. The three display limit is likely a limitation of the dual video cards.
  13. Dalton63841 macrumors 65816


    Nov 27, 2010
    This here. It's actually quite simple. It's a sum of total graphics power. If you just have a few regular displays it can probably run about 12 of them. 1080p displays like 6 or 8 of them.

    Saying it can handle 3x 4k displays is their cool way of saying, "This setup can handle pretty much everything you could want to do.
  14. gjarold thread starter macrumors regular

    Nov 14, 2007
    Right, that's the obvious interpretation, BUT, it makes no sense for the number to be 3.

    If there are two cards, then bandwidth limitations would imply a max of 2 or a max of 4.

    A max of 3 makes no sense...
  15. VirtualRain macrumors 603


    Aug 1, 2008
    Vancouver, BC
    Does the Ivy Xeon being suggested for this system also have a GPU on-die?

    If so, does that mean there could be 3 GPU's? (Integrated Intel + 2x AMD?)
  16. ender78 macrumors 6502

    Jan 9, 2005
    The GPUs will be SLId, take total horsepower of both GPUs and associated video RAM, Apple calculated that they could drive three displays. Three displays is likely on or two more than most people will need to drive. This may actually be closer to 6 displays at 2K.
  17. gjarold thread starter macrumors regular

    Nov 14, 2007
    Isn't triple monitor pretty much de facto standard for pro users ?

    Why bother with any of this if you can do your work on a single screen ? Just get the imac, right ?

    Three is, in my opinion, the *minimum* number of displays this device needs to drive...
  18. ender78 macrumors 6502

    Jan 9, 2005
    Three 4K displays at 27"+ take a up a LOT of desk space. In the photography space, two displays is the norm.
  19. ZMacintosh macrumors 65816


    Nov 13, 2008
    well it would make sense to me that its 3 4K displays.
    if there are 3 Thunderbolt Controllers then the highest/max Thunderbolt device will probably consume most of that TB port/controller.

    So it'd be practically one 4k Display per controller.
    leaving the other Thunderbolt ports either for devices such as a pegasus, or non-video device perhaps.
  20. Tesselator macrumors 601


    Jan 9, 2008
    Yeah, he actually called them "Firewire controllers" though. I guess a slip of the tung?
  21. Stetrain macrumors 68040

    Feb 6, 2009

    It's hard to say at this point since we don't have a ton of Thunderbolt 2 information yet, but I think the following scenario is fairly likely considering what we know about TB 2 and how Thunderbolt behaves on the retina Macbook Pros which have two ports:

    There are 3 Thunderbolt controllers (2 ports each).

    Each controller can drive two 2560x1600 displays (either daisy chained from one port or one per port). This is true of the two-ports-one-controller setup on the current retina Macbook Pros.

    Each controller can drive one 4k display. I'm guessing that that is instead of the 2x 2560x1600 displays.

    So 3 controllers, each can drive either 1 4k display or 2 1600p displays.

    Which would let you do the following combinations:

    3x 4k displays
    2x 4k displays and 2x 1600p displays
    1x 4k display and 4x 1600p displays
    6x 1600p displays

    Definitely doing a lot of speculating here but it makes the most sense to me.


    The PCI-E channels are separate from the Displayport channels with Thunderbolt.

    A 4k display will probably consume the whole Displayport channel for one controller chip (set of two ports), but would leave the PCI-E channels fully open for use for things like ports on the back of the display or other TB devices.
  22. gjarold thread starter macrumors regular

    Nov 14, 2007

    Ahh, interesting. Thanks.

    Now, theoretically, 4x pcie (which I think is what the pcie lines in TB are) is enough to drive 1920x1200, right ?

    So even if I maxed out the display portion with 3 @ 4k, I could still do some kind of pcie attached external GPU doohicky ?

    Do those exist ?
  23. adder7712 macrumors 68000


    Mar 9, 2009
    Sandy Bridge-E and Ivy Bridge-E lack on-die GPUs.
  24. theSeb macrumors 604


    Aug 10, 2010
    Poole, England
    Yeah, he said something along the lines of, "6 firewire 2 ports with 3 controllers. You guys that use this know it's great stuff". That was a bit embarrassing and I understand now why some of the sites initially reported 6 x FW2 ports - just blindly typing away.

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