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
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.
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
I haven't tried it, but Turn any Mac or iPad into a second display...
Review by NAK005, you may not be happy with it…
https://discussions.apple.com/thread/251259038?answerId=252422503022#252422503022
Unfortunately, Target Display mode is not supported on 2015 5K iMacs nor on 21.5" imacs after 2014.
See here: Use your iMac as a display with target display mode - Apple Support
Read about some streaming usb boxes for gaming streamers which could in theory work but if it did likely at a much higher cost that purchasing a new monitor, also a monitor use a lot! Less power than an iMac if you care about the envioment of your electric bill
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.
Is there a solution other than TDM? And I feel like people have stated they’ve gotten it to work... 🤷🏼♂️
I shouldn’t have to spend money for a feature that should be standard! C’mon @apple... can you make this a feature again??!!
That’s because Target Display Mode is no longer available on 2015 and later iMacs and requires 10.13.6 or earlier! iMacs are computers, they are not external displays, it is that simple.
I know... I guess I was just venting. Sorry. Thank you for the helpful suggestions.
Understand , but sometimes it is worth it to spend $150 for an inexpensive display and you are done.
Using a 2nd iMac as an external display
