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I've run an iMac as an external display for a Mac laptop before, but am wondering if my new setup can work like that. I have:

  • 2011 Macbook Air with Thunderbolt
  • 2009 iMac with Mini DisplayPort
  • mini DisplayPort cable

Can I drive my iMac from my laptop? I've had no success so far, despite manually putting my iMac in Target Display Mode using cmd-F2. I can get the setup to the point where both screens turn blue (as expected) but then my iMac reverts to showing the iMac's desktop, not that of the laptop.

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What size display is your iMac? – Matt Love Feb 12 '12 at 12:28
It's a 27" iMac – lowellk Feb 13 '12 at 19:57
Are you using a Mini DisplayPort cable or a Thunderbolt cable to make the connection? – CajunLuke Feb 14 '12 at 3:12
mini displayport – lowellk Feb 14 '12 at 3:22
up vote 8 down vote accepted

According to this source, this should work. This other source confirms it. These are the troubleshooting steps I would try:

  • Run all software updates on both the iMac and MacBook Air. A lot of times there are firmware updates that address issues like this.

  • Open System Preferences > Displays and click Detect Displays.

  • Reset the PRAM on both the iMac and the MacBook Air by restarting the computer and holding ++P+R on boot but until you hear the POST chime twice. Then you can let go and boot normally. Be sure to do this on both machines.

Try going through these steps and let me know if you're able to resolve the issue.

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Flashing the PRAM worked! – lowellk Feb 14 '12 at 9:02
Great! I've had this issue before when I was at Apple. A lot of display settings are stored in the PRAM and resetting it when you run into issues will usually do the trick. – Matt Love Feb 14 '12 at 15:54

Yep, this should work no problems at all. Here is the relevant support article from Apple on the steps to take.

Actually, no. It looks like Macs with Thunderbolt will only use Target Display Mode with other Thunderbolt equipped Macs. This is according to Macworld and also TUAW

Hope this helps.

share|improve this answer
Thanks, but I read that article before posting here. It mentions nothing about Thunderbolt. – lowellk Feb 14 '12 at 3:20

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