Use a 27″ iMac as an external display for another Mac
One of the coolest features of the 27″ iMac is it’s beautiful LED screen with it’s 2560×1440 resolution, and the ability to use that gorgeous display as an external display for another Mac. This is easily done using Target Display Mode and the 27″ iMac’s video input.
What you need to use the 27″ iMac as an external monitor for another Mac
Once you have the hardware, just plug the Mini DisplayPort to Mini DisplayPort cable from the source machine into the iMac and the iMac should automatically enter into Target Display Mode and show video from the source machine. If for whatever reason that doesn’t work, hit Command + F2 to enter in and out of Target Display Mode on the 27″ iMac.
As far as I know this only works on the 27″ iMac, I don’t think the smaller screened iMac’s have this ability in their current revisions.
The CultOfMac has an interesting solution that involves daisy-chaining together standard Mini DIsplayPort to DVI cables to get the same effect, but it’s a lot better to just get the proper cable since they aren’t too expensive. They also have a nice video showing the 27″ iMac being used as an external display for a MacBook Pro and it’s a handy resource if you’re having any troubles.
For more information check out Apple’s Knowledge Base article on the topic.
[ above image via CultOfMac ]