The matrix is simple - matched icons on the ports is a winning combination.

Video in requires matching cable and port on the sending mac. (If all don't match, it won't work.)

Display mirroring (where an iMac can receive video input) only works thunderbolt to thunderbolt or displayport to displayport and isn't backwards compatible where a displayport monitor will work when connected to a thunderbolt mac.

The matrix is simple - matched icons on the ports is a winning combination.

Video in requires matching cable and port on the sending mac. (If all don't match, it won't work.)

Display mirroring (where an iMac can receive video input) only works thunderbolt to thunderbolt or displayport to displayport

The backwards compatibility between the formats only works when a displayport monitor is connected to a thunderbolt mac.

The matrix is simple.

If the icons on the port match, it will work with the proper matching cable. (If all don't match, it won't work.)

Display mirroring where an iMac can receive video input only works thunderbolt-thunderbolt (and of course displayport-displayport works)

The matrix is simple - matched icons on the ports is a winning combination.

Video in requires matching cable and port on the sending mac.   (If all don't match, it won't work.)

Display mirroring (where an iMac can receive video input) only works thunderbolt to thunderbolt or displayport to displayport and isn't backwards compatible where a displayport monitor will work when connected to a thunderbolt mac.