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I'm referring to the 2015 Macbook Pro, 15-inch, with the AMD Radeon R9 M370X with 2GB GDDR5 memory. Can this drive two Ultra HD monitors (3840 x 2160) at 60FPS each? If so, would you be able to simultaneously use the built-in display?

To be clear, I'm referring to SST (single-stream transport) monitors, not MST (multi-stream transport).

You'd have to plug each monitor into a Thunderbolt port, since HDMI supports only 30FPS. Are both Thunderbolt ports on different Thunderbolt buses, or the same? In the latter case, there may not be enough bandwidth.

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According to this document https://support.apple.com/en-us/HT204154 The MacBook Pro (15-inch and 17-inch, Early 2011) and later have Thunderbolt2 and can handle two thunderbolt displays (2560x1440).

According to this document https://support.apple.com/en-us/HT202856 The MacBook Pro (Retina, 15-inch, Late 2013 and later) can handle one MST 4K display at 60Hz.

You can run one 4K monitor off of the Thunderbolt display at 60z and a second off HDMI at 30Hz. the two thunderbolt ports are connected. Once you try to connect a second 4K monitor to the other port, you will go over the bandwidth and the second monitor will go dark.

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  • I clarified the question to say that I'm talking about SST monitors, not MST. Do you have a source for "you will go over bandwidth"? Or is it from personal experience?
    – Kartick Vaddadi
    Jul 21, 2015 at 1:46
  • 4K@60Hz is required up to 16Gbps. Thunderbolt2 is comprised of PCIe2.0 and displayport1.2 wrapped into one. The bandwidth of Thunderbolts 2 is 20Gbps. Math... it's a killer.
    – ZOMGnerd
    Jul 21, 2015 at 11:23
  • Right, I meant to ask: is there a source to back up your claim that both ports are on the same Thunderbolt bus? Thanks for your help.
    – Kartick Vaddadi
    Jul 23, 2015 at 13:50
  • There is only one thunderbolt controller for the MacBook Pro
    – ZOMGnerd
    Jul 23, 2015 at 13:54
  • And one controller means only one bus?
    – Kartick Vaddadi
    Jul 24, 2015 at 13:01
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I was only able to get 60 fps at 2560 on my MacBook 13" from 2015.

You should try hacking around in the Terminal with cscreen. See: https://tomachi.co/60fps-2560x1440-resolution-aoc-u2868-macos/

First just type in cscreen at the terminal to get the ID of your monitor, in my case 78ca19c6:

cscreen
DisplayID Index Depth Width Height Refresh
78ca19c6 1 32 2560 1440 60
use -h to display all usage options

Then issue the command again, this time with the monitor unique ID and the parameters:

cscreen -d 32 -x 2560 -y 1440 -r 60 -i 78ca19c6

Swap 78ca19c6 for the value of your own monitor.

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