Barfeats.com broke a great story not too long ago. The second Mac able to run 5K was none other than the Classic Mac Pro. Apple had to do some Tech Gymnastics to get their 5K iMac to work, as the parts to do so did not exist during it's development.
To some extent, the parts to run 5K STILL don't exist. (DisplayPort 1.3) Dell's UP2715K sidesteps this issue by combining two separate DP 1.2 ports into one feed. Not only does the display need to do this, but the drivers need to as well. And this is where the "Big Breakthrough" came. Nvidia has added the function to their drivers, all we have to do is turn it on. The beauty of this is that it does NOT require turning on "kext dev mode". So your OS is still fully protected by the built-in security features.
Please note that the Dell UP2715K has two choices for input. You can either use a single mDP input for SST 4K mode at 60Hz or the Dual DP input mode which allows for 5K @ 60Hz.
Which GPUs are supported? Any Nvidia GPU from Kepler series (GTX 6xx and GTX 7xx) or later AS LONG AS IT HAS TWO DP OUTPUTS. This leaves most older Kepler cards off the list. A Quadro K5000 Mac Edition is capable. We have also shown that a GTX 760 with Dual mDP ports can run this display to it's full capability. With the newer Maxwell cards Nvidia has included three DisplayPorts or Mini DisplayPorts in each series design. I strongly advise that when purchasing a new Maxwell GPU that you overlook any shiny features or flashy decals and concentrate on getting a card with the full three DP or mDP ports. These will be much more "future proof" and give you a greater array of choices going forward. Several manufacturers have created cards with fewer DP ports to save money, avoid these.
To enable 5K support requires using the Dual DP cable included with the Dell UP2715K. Sadly, using this function disables boot screen support via our EFI cards.You will note that one DP cable is "Primary". This cable alone carries 4K support. If a boot screen is needed, you can use the single DP port in 4K mode and you will get a 4K boot screen. Note that switching between these modes requires use of the buttons on lower right bezel to check and/or change modes.
So, let's begin. You just unboxed your Dell UP2715K and are eager to get it up and running. First order of business is to have the GPU running perfectly. Using a legacy display is easiest for this.
1. You MUST be running OS X Yosemite. As of the date of this writing, the latest version is 10.10.2. You will also need to run the beloved "Security Updates", get them both installed before going forward. (2015-002 and 2015-003)
2. Once you have Yosemite up to latest version it is time to install your Nvidia Web Drivers. We have them linked from the FAQ pages. Note that OS X Build Number is what the driver is keyed to. We will have a separate page dealing with this in the future, just note for now that the driver download page has the Build Number that each driver is designed for.
3. If you get a prompt to update to 10.10.3 or a future Security Update... WAIT ! Come check with us first as clicking "Install" on one of those before an updated Nvidia Driver has been released will result in a miserable experience. 10.10.2 with Update 2015-003 and Web Driver 343.02.f04 was working just fine, no need to instantly click that "install" button.
4. Once you have installed the Nvidia Driver for your OS Build number, verify that it is loaded and running. The easiest way to do this is to click the Nvidia logo in the task bar at the top of your screen. Under this you will see 2 drivers to choose from, one will have a check by it. You want to be sure that the check is by "NVIDIA Web Driver". When the checkmark is by "OS X Default Graphics Driver" you will find that Maxwell GPUs will only have very limited function courtesy of the EFI drivers loaded at boot. With non-EFI cards you will see nothing.
5. If you haven't installed your Maxwell card, now is a good time to do so. If you are still on a "legacy" display you should see a lovely boot screen followed by your desktop. Verify again that the Nvidia Web Driver is running.
6. Here is where it gets interesting. By default 5K support is turned off, you'll need to turn it on. You will need to open the "Terminal" application. It is in the "Utilities" folder inside the "Applications" folder. I keep an icon in the dock for quick access. If you type nvram -p you will see contents of NVRAM. The "boot args" section should show "nvda_drv=1". This is what tells OS X at boot time to load the NVIDIA Web Driver instead of the OS X Default Driver. You need to add to this to turn on 5K mode. Type this command as it appears below:
sudo nvram boot-args="kext-dev-mode=1 nv_spanmodepolicy=1"
After you hit Enter, you will be prompted for your admin password. Type it and hit Enter again.
7. To verify that you did this correctly, once again type nvram -p. You should now see:
8. Now it is time to try 5K! Turn off the machine and connect the Dual DP cables. Any of the DP ports on the GPU should be fine, if you find otherwise please let us know. Verify that the monitor is in Dual DP 5K mode via the onscreen display.
9. Boot your Mac Pro. You will NOT see a boot screen, if everything has gone well you will see the desktop appear. At this point check what displays it thinks are attached. I suggest Display Menu, an inexpensive app that makes this easier. I will be updating this post with images from that app. If all has gone well, you will see that the Dell has appeared not once but twice. One instance will be the one you see, running somewhere between 1920x1080 and 3840x2160, the other instance will be a small, oddball monitor that is 848x600 or so. This is a GOOD SIGN ! You are almost there. I suggest having a 2nd display connected at this time if possible.
10. Reach the control buttons on the Dell and push the power button to turn display off. Wait 5 seconds or so and hit it again, turning on the display. If all has gone well you will come back to a glorious 5K image at a full 60Hz. If instead you see a smeared image that only holds top right corner of desktop you will need to unplug the display and wait for a full minute before powering back up. I had this issue the first time I tried this and was convinced I had a bad unit.
11. You will find that 5K on 27" means TINY text. You will either need to scoot right up to the screen or use a "Retina" mode. Display Menu makes this easier as it shows the Retina modes in white and the regularly scaled modes in black. I frequently use 2560x1440 as it looks perfect.
12. If you need to do diagnostics, or install updates I suggest that you switch to 4K mode and use a single DP cable. (mDP into monitor) This allows 4K boot screens for "under the hood" type work. Note that 4K boot screens only appear on Maxwell series cards. Older Kepler cards like the GTX760 Dual DisplayPort card and the Quadro K5000 will NOT display 4K boot screens. This obviously also applies to any other previous DP card. We may at some point look into adding 4K boot screens to some past cards.
This is the first of many MacVidCards blog posts. Please feel free to point out any mistakes or any suggestions that could inprove clarity.