The MacPro6,1 and iMac15/17 perform special functions on their specific OEM GPUs/Displays. The MacPro6,1 unloads 1 GPU (with no ports) and leaves one functional for it's pseudo CrossFire function. The iMac15/17s apply a special EDID for their 5K displays. The following snippet is taken from /System/Library/Extensions/AppleGraphicsControl.kext/Contents/PlugIns/AppleGraphicsDevicePolicy.kext/Contents/Info.plist: Code: ... <string>com.apple.driver.AppleGraphicsDevicePolicy</string> <key>Config1</key> <dict> <key>GFX1</key> <dict> <key>unload</key> <true/> </dict> </dict> <key>Config2</key> <dict> <key>GFX0</key> <dict> <key>EDID</key> <dict> <key>0610ae02</key> <data> AP///////wAGEAOuAAAAAAwYAQS1 PCJ4IsgFp1VLoCYMUFQAAAABAQEB AQEBAQEBAQEBAQEBAAAAEAAAAAAA AAAAAAAAAAAAAAAAEAAAAAAAAAAA AAAAAAAAAAAA/ABpTWFjCiAgICAg ICAgAAAAAAAAAAAAAAAAAAAAAAAA Ai0CAx6BcPoQAAASejH8eL3MApCI UdNo+hAA9fn6//8AAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAknATeQMAAwAUgG4BhP8TnwAv gB8APwtRAAIABAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAMeQ </data> <key>0610ae06</key> <data> AP///////wAGEAeuAAAAABsZAQS1 PCJ4IAAAAAAAAAAAAAAAAAABAQEB AQEBAQEBAQEBAQEBAAAAEAAAAAAA AAAAAAAAAAAAAAAAEAAAAAAAAAAA AAAAAAAAAAAA/ABpTWFjCiAgICAg ICAgAAAAAAAAAAAAAAAAAAAAAAAA AaZwE3kDAAMAFIBuAYT/E58AL4Af AD8LUQACAAQAf4EY+hAAAQEAEnYx /HixmQIQiGLT+vj4/v//AAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAA AAB3kA== </data> <key>0610ae0a</key> <data> AP///////wAGEAuuAAAAABoZAQS1 PCJ4IAAAAAAAAAAAAAAAAAABAQEB AQEBAQEBAQEBAQEBAAAAEAAAAAAA AAAAAAAAAAAAAAAAEAAAAAAAAAAA AAAAAAAAAAAA/ABpTWFjCiAgICAg ICAgAAAAAAAAAAAAAAAAAAAAAAAA AaNwE3kDAAMAFIBuAYT/E58AL4Af AD8LUQACAAQAf4EY+hAAAQEAEnYx /Hix/wIQiGLT+vj4/v//AAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAA AAARkA== </data> <key>index</key> <integer>0</integer> </dict> <key>unload</key> <false/> ... <key>ConfigMap</key> <dict> ... <key>Mac-42FD25EABCABB274</key> <string>Config2</string> ... <key>Mac-65CE76090165799A</key> <string>Config2</string> ... <key>Mac-B809C3757DA9BB8D</key> <string>Config2</string> ... <key>Mac-F60DEB81FF30ACF6</key> <string>Config1</string> <key>Mac-FA842E06C61E91C5</key> <string>Config2</string> ... For non-Apple hardware, This can cause your GPU not to send a signal to your monitor (black screen) at boot while using the MacPro6,1 (Mac-F60DEB81FF30ACF6 board-id), or iMac15 (Mac-42FD25EABCABB274 or Mac-FA842E06C61E91C5 board-ids), or iMac17 (Mac-65CE76090165799A or Mac-B809C3757DA9BB8D board-ids) system definitions. If this is happening to you, your system will still be responsive but have no signal coming from the GPU's ports to the monitor. How to verify that your system is functional except for video: 1. Share the screen from another Mac on your network to control the system and verify that it is functional and responsive (you must have Screen Sharing enabled). NOTE: You should be able to boot using nv_disable=1 to enable screen sharing if you have a Nvidia GPU. 2. Use a keyboard shortcut to verify that the system is responsive: • On a Apple keyboard, the eject key will open and close my optical drive. • On a Apple keyboard, the play button will launch iTunes and hitting it a 2nd time will start playback depending on what state the app was in when I quit it last. • On a Apple keyboard, control + eject will bring up the the "Shut Down" dialog window with the default button being "Shut Down". When you hit enter/return it causes the default button to activate and the system will shut down properly. • Holding down control + option + command and then pressing the power button on your case or mobo quickly (less than 1 second) will cause open apps to quit and the system will shut down properly. NOTE: Holding down the power button for 5 seconds will cause the system to hard power off and this is not proof of response from OS X (this is how you force a frozen system to power off). If your system is unresponsive (frozen) with a black screen, the fixes outlined here probably won't help you. Fixes: PikeRAlpha outlined a fix for MacPro6,1 in his blog post on May 1st, 2014 where he changed Config1 to none in the above mentioned info.plist. This seems to work for the iMac15/17s as well by changing Config2 to none. Many people have been looking for a Clover "on the fly" info.plist patch to be done at every boot but it fails because Clover's info.plist patches are only visible in the kext caches and it doesn't change the actual info.plist file. It seems that more than one kexts are reading the ConfigMap from the info.plist in it's actual file path, so putting "none" in the kext cache changes nothing. This also makes it impossible to use the dummy kext method. Even if you get a dummy kext with a patched info.plist to load instead of the original kext, the info.plist will still be read from the original kext's file path. Pike came to the rescue (sort of) again on November 23rd, 2015 with a Clover "on the fly" binary patch for the AppleGraphicsDevicePolicy.kext Code: <dict> <key>Comment</key> <string>AppleGraphicsDevicePolicy (board-id) Patch (c) Pike R. Alpha</string> <key>Find</key> <data> Ym9hcmQtaWQ= </data> <key>Name</key> <string>AppleGraphicsDevicePolicy</string> <key>Replace</key> <data> Ym9hcmQtaXg= </data> </dict> This patch changes board-id to board-ix in the binary file but only seems to give the desired result if you have 1 discreet GPU. I have have 2. With 2 GPUs, one always unloads and it's unpredictable which one will work. Some people with only 1 GPU also have issues with this patch. EDIT (03/01/2017): vit9696 offered a new solution for those who want an easy fix. I haven't tested this but it sounds like it bypasses the offending functionality of Apple Graphics Display Policy. Because it is a separate pair of kexts, it should not require any actions (re-patching) after updates. Install the Lilu.kext & NvidiaGraphicsFixup.kext in /Volumes/EFI/EFI/CLOVER/kexts/Other. It says it's for MacPro6,1 but omrij confirms it works for iMac15 and pastrychef confirms it works for the iMac 17 board IDs as well. My last easy solution is a AppleScript app (AGDPfix.app) that patches the OEM kext's info.plist via shell scripts. OS X updates usually cause the kext to be overwritten/updated so the app must be run again after updating OS X, but it's a lot easier than manually patching the info.plist every time. I originally created v1.0 for MacPro6,1 only but have now updated it to v1.1 for use with iMac15/17 sys defs as well. Feel free to download and use the app attached below. NOTE: You will need to use the boot argument kext-dev-mode=1 for 10.10 Yosemite, disable SIP or use kext-dev-mode in 10.11 El Capitan and 10.12 Sierra. My preferred method. For those of you using MacPro6,1 and willing to get a little more geeky, assigning the name GFX1 to your GPU in your ACPI tables (DSDT or SSDT) will also work without the need to patch any kexts and you won't need to worry about re-patching anything after OS X updates unless Apple changes the device policy again (credit : dgsga and furter). In this pic from IORegistryExplorer you can see the AppleGraphicsDevicePolicyControlClient loaded on my second GPU (GTX 980) installed in PCI slot 4 (NPE7): In this state, it will not send a video signal from any of it's ports. In the next pic you can see that I have injected my GTX 980 as GFX1 in NPE7 and AGDPCC is no longer loaded to it: Now all ports are functional. It's also worth noting that I have my 1st GPU (GTX Titan X) injected as GFX1 as well. If you currently have GPU injection via DSDT or SSDT, it's as easy as changing the name. Open your DSDT or SSDT in your editor of choice (I prefer MaciASL) and change GFX0, PXSx, PEGx, or whatever it's name currently is to GFX1. Click compile and save it. If you don't currently have have your GPU injected in your DSDT or a SSDT, see this Guide to create one or more SSDTs for your GPU/s. If your ACPI tables assign specific names to PCI devices when they are installed, It is also possible to rename your DSDT's/SSDT's current GPU device name using clover's ACPI patching function. However, some ACPI table sets don't have a dedicated names for installed PCI devices and when the GPU loads, it gets the name "display@0" under IOPP. See RehabMan's excellent guide here. You should also read this post if you feel you might be having other Nvidia Web Driver related issues: Solving NVIDIA Driver Install & Loading Problems However, The solutions outlined here will solve problem 4.