Hello, I hope this hasn't been answered elsewhere. I've searched the forum, but to no avail. All the info I can find is a little confusing. I have a new 15" Retina MacBook Pro and I'd like to use my old iMac 27" (Mid-2010 running 10.10.2) as a monitor. According to Apple (https://support.apple.com/en-ca/HT204592) this is no problem. Just plug the a MiniDP to MiniDP from the iMac's MiniDP to the MacBook's Thunderbolt. But elsewhere I've seen people saying that doesn't work, or that the new OS doesn't have Target Display Mode properly and so on. So, I'm hoping someone here know's whether or not my new MacBook Pro with Thunderbolt can use my old 27" Mac as a monitor with this cable: http://www.amazon.ca/gp/product/B01979VIRS Thanks very much!!! --- Post Merged, Feb 18, 2016 --- According to this document https://support.apple.com/kb/PH19038?locale=en_US : If you have a 27-inch iMac with a Mini DisplayPort , any other Mac with a Mini DisplayPort or Thunderbolt port can use it as a display. Make sure you have a Mini DisplayPort to Mini DisplayPort cable. So this looks like I'm good to go, unless anyone has experienced otherwise?