Target Display Mode let an iMac show the screen of another Mac over a cable. Apple never brought it to the iMacs with a Retina 5K screen or to any Mac with Apple silicon, so on most iMacs still in use the shortcut does nothing. Second Display brings the same idea back as an app.
Where Target Display Mode still works
Apple supports Target Display Mode only on these models:
- iMacs introduced in 2011, 2012, 2013 and mid 2014, with macOS High Sierra 10.13.6 or earlier, connected with a Thunderbolt or Thunderbolt 2 cable;
- 24‑inch and 27‑inch iMacs introduced in 2009 and 2010, with macOS High Sierra 10.13.6 or earlier, connected with a Mini DisplayPort cable.
The other Mac must be from 2019 or earlier, with macOS Catalina 10.15.8 or earlier. So no iMac from late 2014 on, and no Mac with Apple silicon, can use Target Display Mode. Apple: Use iMac as a display with target display mode
What macOS offers instead
- AirPlay. With AirPlay Receiver turned on, a Mac with macOS Monterey or later shows what another Mac sends it over your network. An iMac can receive AirPlay from the 2019 models on, and so can the iMac Pro.
- Sidecar makes an iPad a display for your Mac. It doesn’t work with a Mac as the display.
- Universal Control lets one keyboard and mouse work on several Macs, but each keeps its own screen, so the iMac doesn’t become a display for your Mac.
More, with Apple’s own pages: AirPlay, Sidecar and Universal Control.
Second Display: the same idea, on newer iMacs
Second Display works on any iMac with macOS 12.3 or later: the models from late 2015 on, up to iMac with Apple silicon. The Mac you work on needs macOS 14 or later. Your Mac gets an extra display, as if you had plugged in a monitor, and sends its picture to the iMac:
- over a Thunderbolt cable, lossless at Highest quality when the two Macs keep up with it;
- over Wi‑Fi, Ethernet or a USB‑C cable without Thunderbolt, compressed to suit the connection.
Side by side
| Question | Target Display Mode | Second Display |
|---|---|---|
| iMacs | 2009 to mid 2014 | Late 2015 on, up to Apple silicon |
| The other Mac | 2019 or earlier, macOS Catalina 10.15.8 or earlier | Any Mac with macOS 14 or later |
| Connection | Thunderbolt or Mini DisplayPort cable | Thunderbolt cable, or Wi‑Fi, Ethernet or USB‑C, compressed |
| Start | Command‑F2 on the iMac’s keyboard | An app on both Macs; they find each other on their own |
| Sound | Can play through the iMac’s speakers | Stays on the Mac you work on |
| Back to the iMac’s desktop | Command‑F2 again | Turn the display off in the menu, or quit Second Display on the iMac |
How good the picture is
In our tests a MacBook Pro with M3 Pro sent Highest to an iMac 24‑inch with M1 at 60 frames per second, over a Thunderbolt 4 cable, at 4480 × 2520. The median delay from capturing a frame to that frame being ready on the iMac was about 9 ms; Medium over Wi‑Fi measured about 37 ms on the same two Macs. How we measured the delay
We haven’t measured older and Intel iMacs yet, nor tried the Thunderbolt 2 ports of the late 2015 models. The speed test recommends the quality your two Macs can keep up. Which iMacs can be a display
Good to know before you switch
- The iMac’s own keyboard and mouse don’t control the Mac you work on in this version: use your Mac’s keyboard and trackpad. Keyboard, mouse and sound
- While it waits, the iMac’s screen sleeps like a monitor’s and wakes when your Mac connects. Sleep, wake and the lock screen
- Over Wi‑Fi and Ethernet the picture isn’t encrypted, so use them on a network you trust; on a cable only your two Macs are connected. How your screen travels
Setup takes about a minute: open the app on both Macs, choose a role on each, plug in the cable and follow the steps on the Mac you work on. Set up Second Display on both Macs
More guides: use an old iMac as a monitor, a 27‑inch iMac with Retina 5K as a monitor and an iMac as a monitor for a Mac mini.