Use your iMac as a display with Target Display Mode
Target Display Mode lets you use the built-in display on a supported iMac as an external display for another Mac.
To use your iMac as a display in Target Display Mode, connect it to another Mac using the correct cable (see System Requirements below). Then press Command-F2 on the keyboard connected to your iMac. When you're done, press Command-F2 again.
You need the following to use Target Display Mode:
A Mac notebook or desktop with a Mini DisplayPort or Thunderbolt port. If your Mac has Thunderbolt 3 (USB-C) ports, you can connect it using the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter.
A Thunderbolt cable or a Mini DisplayPort to Mini DisplayPort cable
A supported iMac with OS X v10.6.1 or later
See the list below for iMac models that support Target Display Mode, the type of cable you need to connect that model of iMac, and the kind of port you need on your other Mac.
iMac models you can use as a display, Cable you need, Port you need on your other Mac
iMac (27-inch, Late 2009), Mini DisplayPort to Mini DisplayPort, Mini DisplayPort or Thunderbolt
iMac (27-inch, Mid 2010), Mini DisplayPort to Mini DisplayPort, Mini DisplayPort or Thunderbolt
iMac (Mid 2011-Mid 2014), Thunderbolt, Thunderbolt
iMac (Retina 5K, 27-inch, Late 2014) and later iMac models can't be used as Target Display Mode displays.
Use Target Display Mode
Follow these steps to start using your iMac as a display:
Make sure that your iMac is turned on, and the other Mac is logged in to a macOS user account.
Connect the Mini DisplayPort or Thunderbolt cable between the two computers.
Press Command-F2 on the keyboard of the iMac that you want to use as a display.
After you press Command-F2, your iMac displays the desktop from the connected Mac.
If Command-F2 doesn't work
If your iMac doesn't switch to Target Display Mode when you press Command-F2, check these things:
Make sure that the iMac you're trying to use as a display supports Target Display Mode.
Target Display Mode works only when your primary Mac is logged in to a macOS user account. For example, if your first Mac is at the FileVault login screen, pressing Command-F2 on your iMac does not enable Target Display Mode. You must first log in to your Mac (using a regular display, if necessary) before you can use an iMac in Target Display Mode.
Make sure that you're pressing Command-F2 on the keyboard that's connected to the iMac you want to use as a display.
In Keyboard System Preferences, if the checkbox is enabled for "Use all F1, F2, etc. keys as standard function keys," the key combination changes to Command-Fn-F2.
Make sure that your Mini DisplayPort or Thunderbolt cable is connected to both computers.
If you're currently logged in on the iMac you want to use as a display, try logging out to return to the login window. Then press Command-F2 again.
Some older Apple keyboards and third-party keyboards might not allow Command-F2 to toggle display modes. If this happens, use the keyboard that came with your iMac to toggle Target Display Mode on and off.
If your iMac is currently started up in Windows, it won't enter Target Display Mode. Target Display Mode isn't supported in Boot Camp.
Exit Target Display Mode
To leave Target Display Mode, press Command-F2 on the iMac keyboard again. Your iMac also exits Target Display Mode if you disconnect the cable that connects the two computers, or if you shut down or sleep either computer.
If the connected Mac goes into sleep mode, the iMac screen turns off until you wake the other computer, or until you take your iMac out of Target Display Mode.
You can control the brightness of your iMac display while it's in Target Display Mode from a connected Mac. Use the Displays pane of System Preferences on the connected Mac, or use the brightness keys on the keyboard of the connected Mac.
To hear audio from a connected Mac using the built-in speakers of your iMac, select the iMac from the Sound pane of System Preferences. You can also use the sound and media keys on the keyboard of the connected Mac to adjust volume and control playback of iTunes and other media.
Connect more than one display
You can use multiple iMac computers as displays as long as each iMac is directly connected to a Thunderbolt port on your computer using a ThunderBolt cable. Each iMac you connect as a display counts towards the maximum number of simultaneously connected displays that your Mac supports.
Avoid trying to connect (chain) iMac computers that are in Target Display Mode to each other. Each iMac in Target Display Mode should be connected directly to a Mini DisplayPort or ThunderBolt port directly on the Mac where you want to use it as a display.
Use apps on your iMac
Any apps that are open on your iMac remain open and active while your iMac is in Target Display Mode. For example, if you begin playing music in iTunes on your iMac and then activate Target Display Mode, iTunes doesn't pause on your iMac.
If you've set your iMac to automatically log out, apps are paused or closed when this happens but your iMac remains in Target Display Mode.
Connect devices to your Mac
A Mac that's connected to an iMac in Target Display Mode can't use the iMac computer's built-in camera, its USB, ThunderBolt, or FireWire ports, or devices connected to those ports. To use external devices with your Mac, connect these devices directly to the Mac that you want to use them with.
Published Date: March 10, 2017