Q: Does the 21.5" iMac support TDM or not?

Thanks. That was helpful. The table in the link does not specify the size for iMacs 2011. Does that mean TDM is supported in screen sizes other than 27", provided the right cable (thunderbolt) is used?

You need to read and comprehend better, misinformation is not helpful.

You are correct, the information IS very clear which iMacs support TDM, that includes ALL Mid 2011, 2012 and 2014 ( with the exception of Retina models), the 21.5" non-Retinas from 2011 onwards DO support TDM; if you cared to read this thread you'd have read that Star Eater has used their 2011 21.5" in TDM successfully.

There is a lot of arrogance in the Apple community, but it is much much worse when the arrogance is based on ignorance.

It is ALL non-Retina iMacs from 2011 onwards, it is a matter of having a Thunderbolt port, and nothing to do with screen size!

There is confusion, and some posters say that no 21.5" iMac can support TDM, despite other posters saying they are already using it!

Reading something and getting confused is fine, but reading something and getting an answer that is the opposite to what is being said is a rare and astounding skill :-)

The website, several people have commented that they are already using TDM on non-Retina 2011 or newer 21.5" iMacs...

To all the folks going "Why are you responding to an old thread; the thread is still relevant, several people have come here for enlightenment regarding the subject, and have left with more confusion because 'intelligent' 'experts' are stating 'facts' that are the reverse of the information the product manufacturers are giving.

Why do people state as fact something that is so obviously wrong?

It's very simple really. Here is the support page for TDM which includes which Macs work and which don't.

Use your iMac as a display with Target Display Mode - Apple Support