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Extending a screen between two iMac

I have an old (late 2012) iMac 27'' running El Capitan and would like to use it as a second screen for my newer (2020) iMac running Monterey. I managed to have the El Capitan iMac to mirror my Monterey screen but got stuck to make the setup of an extended display.

Any ideas of what could I try?

Thanks in advance!

Alumīnija iMac

Posted on Jul 28, 2023 1:19 PM

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Question marked as Top-ranking reply

Posted on Jul 28, 2023 1:30 PM

Unfortunately, that's not possible. Both Macs are too new. This Apple document describes what is needed for Target Display Mode: Use your iMac as a display with target display mode - Apple Support


9 replies

Jul 29, 2023 9:31 AM in response to Agris

Are you trying to do this with with Target Display Mode (TDM)? If so, the 2012 is capable but the Mac sending the video signal must be 2019 and older and running no higher macOS than 10.15 "Catalina."


The very restrictive hardware and OS requirementf for TDM are here: Use your iMac as a display with target display mode - Apple Support


When I had two fully TDM-capable Macs (a 2012 Macbook Pro sending to a 2010 iMac 27, I could not get extended desktop as a option, only mirroring. I alway counted that among TDM's numerous deficits.


If you need extended desktop on your 2020 iMac with no image lag, a proper external monitor is the best and most cost-effective way to get it. The Thunderbolt cabling and adapters required for setting up TDM on even supported newer Macs can, at US$60-90, approach the cost of a decent external monitor.


Jul 29, 2023 10:10 AM in response to Agris

A 27" Late 2012 iMac supports Thunderbolt Target Display Mode. Unfortunately, the newer Mac cannot use the 27" Late 2012 iMac as a TDM display. So there's no point on spending $80 on a Thunderbolt hookup ($50 for a TB3-to-2 adapter, $30 for a TB1/2 cable) to see if it would work. You'd just be out $80.


Reference: the very restrictive requirements in this support article:

Use your iMac as a display with target display mode - Apple Support


Jul 29, 2023 3:14 AM in response to Old Toad

Well, I get that the Target display mode is not the way to go. I just want to make the AirPlay Display mode to work properly.

In the Displays preference pane on my old iMac, the AirPlay Display shows up and I can select my newer iMac from a pull-down list of AirPlay displays. The point I am struggling with is the actual connection. Which is strange because I already have the newer iMac's display mirrored on the old one.

Extending a screen between two iMac

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