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Equipment: Early 2015 MacBook Pro - Retina 13" with the Intel Iris 6100 graphics. Two Dell U2414H monitors. One MiniDP to DP cable connecting MBP to monitor #1. DP to DP cable connecting monitor #1 to monitor #2. OS X 10.11.6.

History: According to the specs for the Early 2015 13" MBPr the laptop is capable of supporting "Dual display and video mirroring: Simultaneously supports full native resolution on the built-in display and up to 3840 by 2160 pixels on up to two external displays, both at millions of colors."

According to Apple Support article HT206587 the video card does "support multi-stream transport (MST) displays at 60 Hz".

According to http://www.displayport.org/cables/driving-multiple-displays-from-a-single-displayport-output/ support of MST 1.2 means the laptop should provide "the ability to stream independent video displays from a single desktop or notebook video output".

Lastly, according to https://software.intel.com/en-us/articles/quick-reference-guide-to-intel-processor-graphics the video card is in fact capable of supporting DisplayPort 1.2.

Problem: When I connect both monitors to the MBPr and "Enable 1.2" on monitor #1, the screen from #1 is mirrored on monitor #2. After doing some research, it appears that I need to change a setting to switch from mirrored mode to extended mode in order to have two different screens. I did Enable 1.2 on monitor #2 as a test but there was no change.

Support: I called Apple and was told to call Dell. I called Dell and the tech informed me that it was definitely a problem with the source and explained how on a Dell PC you could switch between mirror and extended modes within the graphics settings. I again called Apple and spoke with a senior advisor. I was first told that it could only be done using Thunderbolt cables. I directed his attention to the support article and said the listed Dell monitors did not have Thunderbolt. I was then told my video card didn't support that feature but explained that he was referencing the AMD Radeon R9 M370X card which is not my card. He said he would escalate the issue.

Question: How do I enable extended mode?

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The first thing you should try is resetting the PRAM/NVRAM.

Resetting your PRAM/NVRAM

Older Macs had what's called Parameter RAM (PRAM), newer Macs use Non-Volatile Random-Access Memory (NVRAM). Here’s how to reset this:

  1. Shut down your machine. Yes, a full shut down, not just logging out.
  2. Press the power button and then press the commandoptionpr keys. You have to make sure you press these keys before the gray screen appears or it won’t work.
  3. Hold those keys down until your Mac reboots again and you here the startup chime.
  4. Let go of the keys and let your Mac reboot normally.

Note: When you log back in you may need to readjust some of your system preferences (e.g. mouse speed, time and date/timezone, etc).

For good measure, you could also reset your SMC.

For MacBook Pros, MacBook Airs, and MacBooks where you can’t remove the battery on your own (i.e. it's a built-in battery), here’s what you do:

  1. Shut down your computer
  2. Keep the MagSafe adapter or power cable plugged in.
  3. Press at the same time shiftoptioncontrol (on the left side of the keyboard) and the power button
  4. Let go
  5. Turn your computer back on with the power button.

After doing these resets, try again to use your displays in extended mode. Let us know how you go.

  • can you explain why you think this will help ? other similar questions have had answers that claim MST support is enabled in OSX at a software level , does this solution attempt to address it or is it a generic answer ? – Amias Apr 12 '17 at 9:22
  • Well, the SMC controls a whole range of power management functions, including some that can affect displays. And the NVRAM contains a whole range of system settings, some of which relate to your displays (e.g. resolution, depth, etc) and since your question is about your displays, I thought resetting these was worth a shot. However, this was meant to be the things I'd do next before doing some other steps. E.g. if you can't enable extended display from the System Preferences > Displays > Arrangement tab, then your next step could be booting into Safe Mode to see if that sorts things out. – Monomeeth Apr 12 '17 at 9:56
  • ok so you are just guessing, please be honest about that otherwise you are wasting peoples time , especially as doing what you said will cause a loss of settings with no benefit on this issue. The issue with MST is a driver level one , apple have not enabled MST chaining in their graphics card drivers , its only used for super high res displays not for multiple independent monitors. – Amias Apr 12 '17 at 13:38
  • With respect, I disagree. While the OP talks about MST, the question title was How do I enable extended mode with dual monitors in OS X 10.11.6? and the actual question at the end was How do I enable extended mode? So, it seems to me that we've interpreted the OP's question differently. I'm trying to resolve the question as asked, and you're reading in between the lines as to what the OP may have been trying to do. And, on that point you may be totally correct. :) – Monomeeth Apr 12 '17 at 21:49
  • Regardless, troubleshooting is a process of elimination and since the OP was given the runaround by both Apple and Dell, it was time to eliminate possibilities one by one. I started with the Mac side first and the reason my last sentence was Let us know how you go was so we could proceed to multiple other steps, one by one. Eventually we may have ended up with the Dell monitors, the actual cables, etc to resolve the issue. Or we may have ended up with a clarification of what the OP was trying to do. As I never heard back, I assume (and hope) the OP resolved their issue. – Monomeeth Apr 12 '17 at 21:49

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