Late 2013 iMac doesn't support 4k like the support doc says.

kappy, i think you are the one, who is missing the point.

the old document, saying that the imac 27" late 2013 does "support up to max. 2560 pixels" is outdated, because it is too old. at this time, they were not aware of the technique in 2017.

so could anyone / anybody please confirm seriously, if the imac 27" late 2013 (mine), would support / display a UHD resolution of 3840 pixel or better 4096 pixel?

if yes, up to which size, max. 27" or max. 31,5"?

I have the iMac 27" late 2013 as well and It supports my 4K dell display but only 30hz. This is frustrating because apple indeed said that it supports up to 60hz. And i'm using mDP to DP cable. arrrrggg

Maximum supported resolution on an external monitor:

is it 27" or 21" ?

The spec sheet for the 27" 2013 model iMac shows:

Video Support and Camera

• FaceTime HD camera
• 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
• Support for extended desktop and video mirroring modes
• Support for Target Display Mode via the Thunderbolt port using a Thunderbolt to Thunderbolt cable (sold separately)

Asked and answered, if you were more attentive. 4K is not supported on that model with or without Yosemite.

In the Samsung setup, try setting it to AV mode instead of PC. TV vs. PC mode may

deliver different monitor info to the iMac, there by causing the problem

Also, try powering down the iMac and display. Then power up the display.

Then boot the iMac doing a PRAM reset.

Your right about the specs being out of sync.

Using 4K displays and Ultra HD TVs with your Mac - Apple Support

You can use 4K displays and Ultra HD TVs with these Mac computers:

• MacBook Pro (Retina, Late 2013 and later)
• Mac Pro (Late 2013)
• iMac (27-inch, Late 2013 and later)
• Mac mini (Late 2014)
• MacBook Air (Early 2015)
• MacBook (Retina, 12-inch, Early 2015)

Thunderbolt ports and displays: Frequently asked questions (FAQ) - Apple Support

5. Which Macs have Thunderbolt 2 ports?

The following models are Thunderbolt 2 capable:

• MacBook Pro (Retina, Late 2013 and later)
• Mac Pro (Late 2013)
• iMac (Retina 5K, 27-inch, Late 2014)
• Mac mini (Late 2014)

So it isn't just a case of Late 2014 iMac's having TB 2 ports at least for 4K.

Try this fabulous utility Retina display menu http://www.reddit.com/r/apple/comments/vi9yf/set_your_retina_macbook_pros_resolu tion_to I use it to run my 21.5" iMac at 1280 x 720 HiDPI, text looks amazing sharp and all apps work fine at this resolution. It also works with external displays.

I have a late 2013 27' iMac and it does support 3840x2160 on a Dell P2715Qt. The only problem is that it supports it in 30Hz only and I haven't been able to get it working in 60hz.

What port / cable are you using? I've heard that to get 60Hz you should use mini displayport to displayport.

Wow, not helpful.