Target Display Mode on Late 2009 and 2010 iMacs was a pretty neat trick; you connected the iMac to another Mac via the Mini Display Port connector, and the iMac’s display became a second monitor for the first Mac while the system ran “headless” underneath it. When you unplugged the cable, the iMac’s display reverted back to the iMac itself.
The Thunderbolt port in the 2011 iMacs adds a couple of twists to this setup. First, when using Thunderbolt-equipped iMac as a display, you need to hit Command-F2 to switch the display between the iMac and the other Mac. This, however, is a relatively minor inconvenience or even a benefit, depending on how you generally use your iMac.
iMac Compatability List
Most non-retina iMacs from 2009 and later can work in target display mode. This includes:
- iMac (27-inch, Late 2009)
- iMac (27-inch, Mid 2010)
- iMac (21.5-inch, Mid 2011)
- iMac (27-inch, Mid 2011)
- iMac (21.5-inch, Late 2011)
- iMac (21.5-inch, Late 2012)
- iMac (27-inch, Late 2012)
- iMac (21.5-inch, Early 2013)
- iMac (21.5-inch, Late 2013)
- iMac (27-inch, Late 2013)
- iMac (21.5-inch, Mid 2014)
Another wrinkle comes in the form of what computer can connect to which iMac with which cable. To determine this, we ran eight simple tests using the following:
- a 2011 iMac (Thunderbolt)
- a 2010 iMac (DisplayPort)
- a 2011 MacBook Pro (Thunderbolt)
- a 2010 MacBook Pro (DisplayPort)
- a Mini DisplayPort cable
- a Thunderbolt Cable.
We attached MacBook Pros to the iMacs in each combination with each cable. If the iMac was able to be used as a display for the MacBook Pro, it passed.
Here are the results we got:
Utilizing a Mini DisplayPort cable allows a Mini DisplayPort equipped iMac to be used as a display on either a Thunderbolt or Mini DisplayPort equipped Mac.
But when it comes to utilizing a Thunderbolt cable, only another Thunderbolt-equipped Mac can use Target Display Mode with a Thunderbolt capable iMac.
No other combinations were viable.
From our testing, we see a few things.
- The only way to use a Thunderbolt-equipped iMac as a display is to hook it up to a Thunderbolt Mac via a Thunderbolt cable.
- The only iMacs that will work as a display for a DisplayPort Mac is one that also has a DisplayPort.
- DisplayPort iMacs require a DisplayPort cable, though they can work with either DisplayPort or Thunderbolt Macs.
- Only get a Thunderbolt cable if you’re going to connect two ThunderBolt-equipped computers together, it won’t work for anything else.
One final “glitch” that’s popped up seems to be relegated to a particular set of circumstances. On our 15” 2011 MacBook Pro when using a 2010 iMac as a display, we found that the video connection became unstable, as in this video.
The only solution that we’ve found for the moment is to hook the MacBook Pro up to a DisplayPort-equipped monitor (not an iMac). Then we let the video go through its connection there. Once reset, we were able to disconnect the MacBook Pro and reconnect it to the iMac.
What have your experiences with connecting display via Thunderbolt been? Let us know in the comments below.