Current OS X 10.10.3 seems doesn't support Dell UP2715K in 5K resolution.

No Mac officially supports 5K resolution on an external monitor. The only Mac that officially supports a 5K resolution is the 27" iMac using its built-in screen.

Note: This also includes the new Mac Pro which cannot do 5K. It can only do 4K but can do 4K to this particular Dell monitor.

Unofficially you can use an old i.e. 'classic' Mac Pro with an Nvidia GTX 980 card. This requires connecting two Displayports from that video card to the Dell monitor, half the pixels are done via one connection the other half by the second connection. This will give you the full 5K resolution.

See http://barefeats.com/mpt5k.html

I disagree with your statement, I’m right now writing you on 5K@60Hz on Dell UP2715K and Mac Pro (Late 2013).

OS X 10.10.3 Yosemite enabled it. I rejoiced.

I think your cable setup is wrong.

Mine are plugged at the first top left (facing the port) mDP port and the second just below.

The monitor reports correctly 5120x2280, 60Hz in OSD.

(and boy, it’s gorgeous!)

And this confirmation.

The post on Netkas in actually mine too😉

As this one is, maybe more telling:

http://forums.macrumors.com/showpost.php?p=20971991&postcount=23

🙂

Which ports on nMP are you using?

You may need to get them on separate TB buses.

For me was super easy, and I have the D300 version.

Both DP cables plugged in to separate TB buses, hit power button and wait. The boot screen never shows but when display pops up, there it is, full 5K.

Make sure both cables are plugged in to correct 5K input and you have Dell in 5K mode.

When I did it I had the right hand mDP cable on 2nd rung down, but that shouldn't make a difference.

Are you certain that the Dell is in 5K mode?

You should see an icon with 2 @ DP cables in upper right corner on occasion.

Also, when you tried in 10.10.2 did you see a 2nd display listed at 848x480 res?

When you switch from "Best for this display" to "scaled", hold "option" key and you should see all possible resolutions.

Also, you may need to power cycle the display. Pull the power plug while computer running. Plug back in after 10 seconds or so and see what happens.

If it is running at 2560x1440 and you unplug the 2nd DP cable, does it cause display to flicker? (Called "hot plug detect"?)

Yay !

Glad this helped.

When I first unboxed my 5K I had same scare, thought I got a dud.

Using the power button didn't work, I had to actually yank the plug.

Sometimes I still have to, it gets in a state.

Hopefully a future firmware update fixes it, but glad to have helped.

hello

unfortunately for me, same machines (mac pro late 2013 and dell up2715k), but no luck, cannot get the full resolution 5120-2880.

i Only have 2560-1440.

though i have dual dp cables connected...

is there anything i am missing.

and i cannot change the resolution under settings >display...

any help appreciated ! :-)

cheers

I'm having all kinds of strange issues. Im running Sierra have. a top spec Mac Pro late 2013, with dual AMD D700 Cards. If I run the display in "default" which is massive I don't have issues. If I run it at full top res at 5k 5120 x 2880 no issues. But any of the scaled resolutions in between and my screen is intermittently flickering. Even the I'm not doing anything, there is distortion and scaliness across the display.

Ive just had the Mac in for replacement graphics cards, graphics board and a thorough checkup.

Im hugely dissapinted with the lack of display effort for this computer. Especially for us professionals. It's shocking the lack of good monitors.

Any advice appreciated.

Cheers

David