MP 1,1-5,1 3-Display-Setup -- MacPro 5,1 + Radeon 7870

[TrumanLA]

MacPro is unable to drive 3 Displays using a GPU with 4 outputs​

Machine-Type: 12c Mac Pro (True 2010 5,1)
MacOS Version: 10.13.6
GPU / Adapter: AMD Radeon HD 7870 Dual-X 2GB
GPU Outs: DVI-D • DVI-I • HDMI • DisplayPort (full size, not miniDP)

Is "an active adapter" required to run 3 HD (1920 x 1200) LCDs with a Mac Pro..?
(I'd been under the impression it was an issue for higher resolution, with the 30in Cinema Displays for instance..?)

2-Display Setup that works:​

Either DVI port + HDMI works to drive 2 displays.​

​

** The 2 DVI ports cannot be used simultaneously.​

** The DP never works (even alone; is this an OS X issue or should he replace the cable and re-try the port..?)​

All displays only use HDMI inputs.​

IF the DisplayPort should work under OSX, I'll order a new DisplayPort --> HDMI cable​

 

[zedex]

If you had a Radeon HD 7950 with standard (Mac) port layout, you would be able to power 3 displays. It is the irregular (PC only) port layout that renders certain display outputs useless. There is more information on this unusual parameter in the early threads on 'activating AMD hardware acceleration'. IIRC it has something to do with "Radeon frame buffers" - that might be a useful search term if you want to research it further. In short - the solution is to obtain a HD7950 with same port layout as HD7950 Mac Edition.. 1xDVI, 1xHDMI, 2xmDP.. though in truth I'd dispense with the plan to acquire a cheap HD7950 and just look for a cheap RX580. Price difference on 2nd hand market is negligible.