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I would like to use my late 2009 "27 iMac as an external display for my 13" 2013 MacBook Air. I've searched the internet and found this thread (and it's sources) that suggests that it is possible to get the setup (as described above) working.

As I said, I have a late 2009 iMac (target) that I connect to my 2013 MacBook Air (source) with a Mini DisplayPort cable. For a moment, the MacBook Air seems to recognize the iMac as the screen on my MacBook air flashes. At the same time the screen on my iMac turns black.

Now, on the MacBook Air, when I have the displays settings window open and click on "detect screens", I am able to select the 2560 x 1440 resulution, which is the resolution of the iMac.

A few seconds later, the screen flashes again on my MacBook Air, and the "detect screens" window has closed. At the same time, the screen from the iMac returns to its original state, showing the desktop of the iMac itself.

Just to be accurate:

  1. I have tried to use the Target Display Mode on the iMac. This automatically turns the screen black and starts the chain of events I described above, with the same results
  2. I've reset the PRAM of both the iMac and the MacBook Air, as this was suggested in this thread. This didn't do anything for me. The chain of events stayed exactly the same as described above.
  3. I made sure both devices were awake when connecting them to one another, with the Mini DisplayPort cable.

As I am reading this thread and its sources, it should be possible to get my setup working correctly, or am I missing something?

I know there are other solutions to get the iMac to work as an external display with an adapter (DVI/HDMI), but this solution won't let me make use of the 2560 x 1440 resolution as DVI/HDMI is max 1920 x 1080.

  • did you try screen sharing ? – Ruskes Jun 18 '14 at 19:04
  • Well, I've tried screen sharing as a solution. But as far as I know, I can't really use the iMac as a second screen (with a different desktop). Screen sharing just shows my iMac desktop on my MacBook or the other way around. What I would like to achieve is to have a second (separate) screen. If this is possible through screen sharing, that would definitely be an option for me. – mrcrazylee Jun 18 '14 at 19:37
  • You’re right, it should work with TDM. – Crissov Jul 9 '16 at 16:14

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