Following new "Using 4K displays..." doc but iMac doesn't work as described

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Level 1

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Following new "Using 4K displays..." doc but iMac doesn't work as described

Recently there was quite a lot of positive chatter as Apple updated its 4K support (see Using 4K displays and Ultra HD TVs with your Mac - Apple Support).

The above document, last amended late-May 2015, appears to supersede the original specs documents regarding resolution support of several Macs including the iMac (27-inch, Late 2013 and later) of which we own several. The document clearly states that the iMac (27-inch, Late 2013 and later) supports the following.

With OS X Yosemite v10.10.3, most single-stream 4K (3840x2160) displays are supported at 60Hz operation.

We own this model of iMac with various GPUs including the maxed out NVIDIA GeForce GTX 780M 4096 MB and in NO CASES can we get it working 4K/UHD @ 60Hz. The very best we've been able to do is to force the monitors to use Multi-Stream Transport where by we can get 4K @ 30Hz (which is barely useable). The main 4K monitor we're trying to use is the Dell P2715Q (which works fine when connected to a MacBook Pro Retina) but not as stated in the document on the iMacs. With single-stream the iMac can only achieve 2560 x 1440 as per its original specs.

Have Apple not released the required update yet for iMacs? Is the document wrong when it comes to the iMac (27-inch, Late 2013 and later) and it therefore should be updated accordingly to avoid confusion? To my understanding it would seem that Thunderbolt 2 would be required connect via DisplayPort 1.2 to achieve 4K @ 60Hz? The iMac (27-inch, Late 2013 and later) are all Thunderbolt 1 (other than the Retina 5K) therefore I don't understand the inclusion of the iMac (27-inch, Late 2013 and later) in the document at all.

Please can Apple clarify as we would love to get this working so we can test our Retina apps.

iMac (27-inch, Late 2013), OS X Yosemite (10.10.3), null

Posted on Jun 1, 2015 10:50 AM

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Answer 1

markwmsn

Level 6

14,999 points

Jun 1, 2015 2:16 PM in response to drschwar

If you want Apple to clarify something, you need to contact Apple, not this user-to-user assistance forum. (We do get a few Apple folk through here, mostly to keep the peace and provide standard answers from canned help documents when a question goes unaddressed for some days. Since your problem is a disagreement between two canned help documents, I don't think the latter group can help you, and the former isn't supposed to try.)

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Answer 2

Jul 9, 2015 11:50 AM in response to drschwar

drschwar,

Unfortunately, I'm in the exact same boat as you...I recently purchased a refurb late 2013 iMac 27-inch (Core i7 3.5GHz, 3TB Fusion, NVIDIA GTX 780M 4GB) in lieu of a r5K iMac after reading the Apple support article you're citing. The reasoning doesn't really...but long story, short...I bought a Dell P2415Q Ultra HD monitor to use at 1920x1080@2x (HiDPI mode) and I can't get it to run at a 60hz refresh rate either. I can set the monitor to run in MST 2 (DisplayPort 1.1) mode which gives me 3840x2160 (@1x) at 30hz using the Dell-supplied mDP to DP cable. I've looked high and low to find anyone else on the internet, YouTube, et al. who has gotten it to work either. I'm not saying it won't, just that my searches have netted me nothing.

I have yet to find any particular reason why the iMac can't drive ONE 4K display at 60z, despite the fact that it only has Thunderbolt 1 ports. The Core i7 CPU supports DP 1.2, the Intel 8-series chipsets support DP 1.2. The only real issue that I see is that the Cactus Ridge Thunderbolt controller only shows as being able to support DP 1.1a. I can't find decent technical specs on DP 1.1(a) on the official DisplayPort website or in the Wikipedia listing.

After doing some digging on Amazon and reading a few reviews, I've ordered an Accell B143B-007J UltraAV Mini DisplayPort to DisplayPort 1.2 Cable to see if this cable allows me to hit 60hz operation. I may also try Apple Tech Support and see if they can help me. It's very frustrating as I like the Dell monitor and HiDPI looks great, but 30hz just doesn't cut it. I'll make sure to report back my success or failure.

Be sure to archive that Apple URL for posterity as it may end up being updated, before all is said and done, and the Late 2013 iMac disappears from that list.

If nothing else work, I do still have a small window available to return the iMac and I may just choose to exercise that option.

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Answer 3

Kerig717

Level 1

8 points

May 12, 2016 2:35 PM in response to zdigital2010

Any luck with the new v1.2 Display port cable? I've got this same problem with my Late 2013 27" iMac. The UHD Dell P2715q works fine on our 2015 Retina iMac, but I can't get 60hz on the 2013 like the document says - only 30hz. Called Apple, but no additional information.

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