x2 iMac late 2013 running Catalina - How to use one as an extended screen to the other?

Question

Level 1

4 points

x2 iMac late 2013 running Catalina - How to use one as an extended screen to the other?

Hi,

Hoping someone can help me here.

I have x2 iMac late 2013 running Catalina, I wanted to connect the two together using one as an extended screen to the other, I have a Thunderbolt cable between the two, but I still don't see an option for this. I have checked the 'System Info' 'System Report' and can see that on both iMac that the Thunderbolt entry in hardware shows an active connection - Device Connected, shows cable firmware as 1.0.16 and a valid serial number for the Apple Thunderbolt cable (which cost a small fortune!).

Please, what am I missing?

Thanks in advance.

Posted on Jun 6, 2023 2:50 AM

Reply

Answer 1

Top-ranking reply

dialabrain

Level 10

135,377 points

Jun 6, 2023 3:10 AM in response to xsiv_one

One of the iMacs has to be downgraded to High Sierra.

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

Reply

Answer 2

Jun 6, 2023 3:46 AM in response to dialabrain

RE: One of the iMacs has to be downgraded to High Sierra.

Specifically, the Late 2013 iMac that is going to act as a Thunderbolt TDM display has to be running High Sierra or earlier. Downgrade one iMac to High Sierra, and try to use the one running Catalina as a TDM display, and things still won't work.

Reply

Answer 3

dialabrain

Level 10

135,377 points

Jun 6, 2023 3:45 AM in response to Servant of Cats

Servant of Cats wrote:

RE: One of the iMacs has to be downgraded to High Sierra…

That's explained in the link I posted. Perhaps you could re-read the link?

Reply

Answer 4

dialabrain

Level 10

135,377 points

Jun 8, 2023 8:36 AM in response to xsiv_one

Did you check this section…

"If target display mode doesn't work" from Use your iMac as a display with target display mode

I have no further suggestions. Personally I've never used TDM.

Reply

Answer 5

xsiv_one Author

Level 1

4 points

Jun 8, 2023 8:30 AM in response to dialabrain

I performed a clean install of High Sierra on one of the iMacs leaving the other on Catalina, but unfortunately I'm still no further forward, pressing Command+F2 on the High Sierra iMac still doesn't give me the desktop from the Catalina iMac. Or maybe I'm missing something? All thoughts welcomed.

TIA

Reply