Yes the previous iMacs sent a signal. Their current computers don’t receive the signal. This is not about the 5K display, you’re missing the core problem. It stopped working when the silicon line came out. You can’t get any iMac to work in target display mode on silicon Macs.

That’s not a technical limitation, that’s laziness. Go read more about this. It simply doesn’t work anymore without 3rd party solutions.

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GeekyBear an hour ago | parent [-]

There is literally nothing stopping you from using a modern iMac as an external display using a thunderbolt connection today.

If you're OK with video compression artifacts, you can even do it over a WiFi connection.

	▲	Forgeties79 2 minutes ago \| parent [-]
		You cannot grab an iMac, plug it into a silicon Mac, and get a picture in the iMac (without 3rd party software). This is incorrect. Please go look this up. The feature stopped working when silicon Mac’s came out. It only works on Intel Macs.