2021 iMac as external display?

[neon44]

Any rumors on next iMac having feature of being external monitor? I have 2017 5K iMac and I love this screen but at the same time I can't use my other devices with this screen. I tried creating remote desktop on thunderbold cable from MacBook and it's okish, but lag is visible and compression kicks in when I change contents quickly. It has similar quality to Sidecar on iPad or slightly worse.

 

[CWallace]

I doubt it - doubly so since there are rumors that Apple will offer a new Thunderbolt Display using the same panel as the 2021 iMac.

 

[sharprichnorth]

I doubt it - doubly so since there are rumors that Apple will offer a new Thunderbolt Display using the same panel as the 2021 iMac.

That didn't stop them from having this capability on my late 2013 iMac, which was being produced at the same time as the old standalone display. Unfortunately they removed this functionality in a later version of macOS.

 

[ADGrant]

That didn't stop them from having this capability on my late 2013 iMac, which was being produced at the same time as the old standalone display. Unfortunately they removed this functionality in a later version of macOS.

I thought they removed it when they went to high dpi screens.

 

[CWallace]

That didn't stop them from having this capability on my late 2013 iMac, which was being produced at the same time as the old standalone display. Unfortunately they removed this functionality in a later version of macOS.

That is because the iMac before 2015's 5K model was not Retina. 5120x2880 is too high for one DisplayPort 1.2 channel to handle so the external displays from Dell, HP and others required to DP 1.2 cables - one driving the left half at 30Hz and one driving the right half at 30Hz.

Apple did not want a 30Hz refresh rate for the iMac 5K, so they developed a custom timing chip that bonded the two DP1.2 channels from the AMD GPU to provide a "seamless" 60Hz refresh rate. This meant, however, that Target Display Mode no longer worked (I am guessing because there were no DP channels left or due to the 60Hz refresh rate).

TB3 and USB4 support higher DisplayPort protocols and have the bandwidth to drive a 5K display over a single channel which is why the LG Ultrafine 5K and similar displays need only one TB3 cable.

I presume the iMac 5K and iMac 4K never had their controller chip upgraded since it worked fine. And with so many years passed, I expect they will not re-enable TDM, but I am sure someone will test it with the 2021 4.5K iMac when they get into tech reviewers hands.

I thought they removed it when they went to high dpi screens.

This is correct, as outlined above.

 

[applesith]

No display in support. I chatted with an apple store rep earlier.