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Using a 2nd iMac as an external display

I have a 27", 5K Retina iMac (late 2015) to which I would like to connect my 21.5", 4K Retina iMac.

Both iMacs are running OS 10.15.6 Catalina

I would like to connect them with an Apple Thunderbolt 2 cable


I have tried *literally all* of the suggestions for TDM (Target Display Mode) with no success. Any assistance would be appreciated.

iMac, macOS 10.12

Posted on Aug 20, 2020 9:55 AM

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12 replies

Aug 20, 2020 1:06 PM in response to yv_band

Your only option would be Screen Sharing via ethernet

or some third party VPN.

Share the screen of another Mac - Apple Support


Depending on what you are doing that may work well enough.


If you truly want to use it to extend your desktop, there is

one possibility though I have never used it:

https://astropad.com/product/lunadisplay/


I have heard others mention it here recently.


Aug 22, 2020 8:13 AM in response to yv_band

if it should be standard or not is a judgment call it never worked with any of the laptops

and only a select few iMacs really


Compatible Macs 

iMac Model *

Port Type

Compatible Mac Source*

2009 - 2010 27-inch iMac Mini DisplayPort Mac with Mini DisplayPort or Thunderbolt

2011 - 2014 iMac Thunderbolt Mac with Thunderbolt

2014 – 2015 Retina iMacs Thunderbolt No Target Display Mode support

* Mac must be running OS X 10.6.1 or later

https://www.lifewire.com/use-imac-as-monitor-with-target-display-mode-2260906


so the feature you feel should be standard had a 5 year timespan on some select iMac models

seems it was removed when the 4k and 5k iMacs came to be so maybe a technical issue in that department


at any rate


This is a user helping other users with tech questions forum, you are not addressing apple here  just  fellow users


you can suggest apple bring it back maybe with their new arm based Macs?

using their feedback channel

https://www.apple.com/feedback/imac.html

Aug 22, 2020 8:50 AM in response to rkaufmann87

I know... I guess I just want there to be some additional functionality. I'm a teacher and have two iMacs in my classroom but really need more desktop "real estate" so it would be nice to have the option of using that 2nd iMac as a 2nd display when necessary and as a 2nd computer when necessary. I'm merely trying to use the resources I have without spending any more $$$ right now. Thanks for your reply.

Using a 2nd iMac as an external display

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