Using Target Display Mode: Turning an Older iMac into an External Monitor
Can an Old iMac Be Used as an External Monitor?
Recently, I found an older iMac for a reasonable price on Karrot Market (a Korean second-hand marketplace) and, after thinking about how I could use it, I tested Target Display Mode. Target Display Mode is a feature that allows you to use iMac models released between 2011 and 2014 as external monitors. The operating conditions were more complicated than I thought, so I've compiled them here.
Conditions for Target Display Mode
To use Target Display Mode, the following conditions must be met:
- Target iMac: iMac models with Thunderbolt ports released between 2011 and 2014 (21.5 inch or 27 inch), with macOS High Sierra or earlier installed
- Host Mac: A Mac using an Intel processor (e.g., MacBook Pro 2018, iMac 2019), macOS Catalina or later versions also possible
- Connection cable: Thunderbolt 2 to Thunderbolt 2 or Thunderbolt 2 to USB-C (Thunderbolt 3) adapter
-
Mode trigger: Command-F2 keys on an Apple keyboard (non-Apple keyboards are less likely to work)
Note that Target Display Mode is not available for Apple Silicon Macs with M1-M4 chips.
Please refer to the
Apple official website link
for more details.
Test Process and Results
First Test: Connecting an iMac 2011 and MacBook Pro 2018
First, I connected a mid-2011 21.5-inch iMac (running High Sierra) to a 13-inch MacBook Pro 2018 with Touch Bar (running Monterey). The necessary items were a Thunderbolt 2 to Thunderbolt 2 cable and an Apple keyboard. I pressed Command-F2 to activate Target Display Mode and, although it didn't connect the first time, it worked after two or three attempts.
After connecting, the iMac screen worked as an external monitor, and the sound output normally. It worked without any issues, even without logging in with the same user account.
Second Test: Connection with iMac 5K
This time, I tried connecting it to an iMac 5K (2019, Monterey). Target Display Mode worked normally even with different user accounts, but the Command-F2 input failed with a third-party keyboard. It worked right away with an Apple keyboard.
Additional Tests and Impressions
Afterwards, I purchased an additional iMac 2011 mid (27-inch) model and conducted additional testing. The larger screen size made the work environment much more comfortable. Of course, there was still a difference in resolution, but there were no major problems with readability.
However, old iMacs were quite thick and heavy, making them difficult to move. Still, the ability to use an Apple-designed external monitor at a low price is a major advantage.
In Conclusion...
Target Display Mode is a great way to use older iMacs as external monitors. Especially for those who use Intel Macs, it can be an opportunity to add a secondary monitor at a low cost (around 100,000 KRW for a 21.5 inch model and 200,000 KRW for a 27 inch model). However, you need to keep in mind that it cannot be used with M1/M2 Macs, and the operating conditions are tricky. The image quality is not comparable to modern monitors but the appearance is great and the combination with other Mac devices is pretty good. (However, the electricity bill is surprisingly high).
If you want to use an old iMac, search for a suitable model on Karrot Market!
