How to use old iMac 5K as a second screen

[iMore Question]

Is there a way to use my old 5K late 2014 as a second display with my new iMac 5K 2019

 

[pkcable]

I'm not sure if it would work, BUT maybe with a thunderbolt to thunderbolt cord? I'm not sure how you could tell the old computer to just let itself be used as a monitor though. You probably would need some sort of software for this, which may or may not exist.

 

[Golfdriver97]

If this is an all in one PC, is it possible to turn on the display without turning on the PC itself?

 

[Lee_Bo]

Doing a quick web search, I came across this article:

https://support.apple.com/en-us/HT204592

Hope it helps.