Required Source Mac: Any Mac with DisplayPort or ThunderBolt port. Required Target iMacs: Mid 2011, Mid 2012. Required Target 27-inch iMacs: Late 2009, Mid 2010. Then press CMD + F2 on the target iMac to switch its display to the source Mac. To activate TDM, have both computers running, not sleeping, and connect the required cable to each Mac. With the right cable, you can connect the MacBook Air to the iMac and use that iMac as either a second display or a mirrored display, giving you a lot more room to work. At home you have one of the qualifying iMacs (see the table below). Let's say you have a MacBook Air with a small display that you use for travel.

The applicable document here is: ' Target Display Mode: Frequently Asked Questions (FAQ).' That Apple document goes into great detail, so I won't repeat it here. However, specific hardware and cables are required. It's not well known, but, for example, a MacBook Pro/Air can connect to and drive a 27-inch iMac display either as an additional display or mirror mode using what's called Target Display Mode (TDM).

Mac mini mid 2010 dual display