I've searched, youtube'd, etc. and just can't find this precise answer. Any help is greatly appreciated. Have 2 2012 iMacs, would like to used one in Target Display Mode as a 2nd monitor with Thunderbolt cable. So after Command f2 to complete the TDM transition to the 2nd iMac ("monitor"), using it for a while then shutting down the computer, does something have to be pressed on the keyboard (keyboard stroke) each and every time the main computer is turned on. And does this require two keyboards each time, one to the computer and the other to the "monitor"? Or is it as simple and turning on the "computer" on both the computer and "monitor" open up identical to the last time it was used?