I have a late 2013, 27" iMac with a GeForce GTX 780M graphics card, which I'm trying to get to connect to two 4k displays (Asus MG28U) at 60Hz. When I connect them, I am limited to 30Hz (but importantly, the 3820x2160 resolution does work):
I also have an early 2015 MacBook Pro, which supports these displays at 4k60. This confirms that the cables I'm using (Mini DisplayPort to Display port) are not the limiting factor). Interestingly, the preference pane looks different on my MacBook Pro, offering a bunch of scaling options, with no mention of refresh rate (although I can visually confirm it's 60 Hz):
I am trying to figure out why these two computers treat these monitors differently, and show different settings for them.
There is conflicting information about 4k support on this Mac. According to Apple's official technical specifications for this (iMac (27-inch, Late 2013) - Technical Specifications), its limited to only 2560x1600:
Simultaneously supports full native resolution on the built-in display and up to a 30-inch display (2560 by 1600 pixels) on an external display
This is clearly (no longer) correct, given then my iMac is running two of these displays at 3840 x 2160 at 30hz.
Apple's page on Mac 4k support (Using 4K displays, 5K displays, and Ultra HD TVs with your Mac) contradicts this, claiming that 4K60 is supported for SST displays (emphasis mine):
With OS X Yosemite v10.10.3 and later, most SST 4K (3840 x 2160) displays are supported at 60Hz on these Mac computers:
- MacBook Pro (Retina, 13-inch, Early 2015) and later
- MacBook Pro (Retina, 15-inch, Mid 2014) and later
- Mac Pro (Late 2013)
- iMac (27-inch, Late 2013) and later
- MacBook Air (Early 2015)
...
Multi-stream transport (MST) displays
These Mac computers support MST displays at 60Hz:
- MacBook Pro (Retina, 15-inch, Late 2013) and later
- MacBook Pro (Retina, 13-inch, Early 2015) and later
- Mac Pro (Late 2013)
- iMac (Retina 5K, 27-inch, Late 2014) and later
Assuming this information is correct (I'm skeptical given the contradictions) this iMac can support 4k60Hz for SST displays, but not MST displays. In that case, I suspect that these Asus MG28U displays use MST, but I cannot find any information regarding whether they're SST or MST.
Has anyone gotten 4k60 to work with a late 2013, 27" iMac? Is there some setting or something that I am missing? Any help would be appreciated.
10.13.2
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