Everyone needs to go to www.apple.com/feedback and tell them to add target display mode back to their iMacs. This feature was available from 2009-to early 2014 iMac models. Apple won't know unless everyone lets them know that was an awesome feature that needs to be added. I am stuck with a 2010 iMac 27 and really can't buy a new iMac without loosing the target display mode on my computer because I connect my laptop to it as well. iMac's are awesome capable computers with beautiful displays that should be used and connected with other devices with the iMac as the target display.