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I have a desktop computer with an Nvidia 9700 GTX graphics card. I'm using the DVI port on the desktop with the Mini-Display Port DVI adapter to plug in to my mid-2011 iMac Thunderbolt port.

I boot the computer in Target Display Mode (holding T at startup), and all I get is the thunderbolt/firewire screensaver, not my desktop.

I'm assuming their might be a different adapter, or that I need a different graphics card? I'm willing to shell out the money, just haven't found a concrete answer on the internet. Thanks.

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2 Answers 2

The Thunderbolt iMacs can only act as a display for other Thunderbolt-equipped computers (Macs only at this point, but once there are Windows PCs with Thunderbolt they should work too). Thunderbolt ports can output a DisplayPort signal, but the input ports (i.e. anything that's a monitor - Thunderbolt Display and iMacs in Target Display Mode) can only take Thunderbolt, not DisplayPort or DVI.

The Apple KB article on the subject: iMac (Mid 2011): Target Display Mode does not work with Mini DisplayPort cable

iMac (21.5-inch, Mid 2011) and iMac (27-inch, Mid 2011) support Target Display Mode via Thunderbolt to Thunderbolt cable (2 m) when the source is another Thunderbolt-equipped computer.

(Emphasis mine)

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Holding T at startup isn't Target Display Mode, it's Target Disk Mode (which turns your computer into a very expensive external hard drive for another computer).

Target Display Mode is activated by hitting Command+F2 when the computer is on.

Some notes:

  • You have to be logged in to the computer being used as a display. If the screen is locked, Command+F2 won't work.

  • If the computer acting as a screen turns on a screen saver which requires a password, Command+F2 won't immediately disable target display mode. To disable Target Display Mode, you'll have to either: (1) disconnect the cable; or (2) move the mouse, type in your password, then hit enter (the same as you would if you could see the screen, even though you can't), THEN hit Command+F2. The first option is far safer from a security standpoint (i.e. what if you computer's screen saver DIDN'T turn on and somebody sent you an IM? You would have just typed your password to them).

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