Currently Being ModeratedSep 3, 2013 11:34 PM (in response to MJSfoto1956)
You have the Mini DisplayPort version of the 27" display. Compare it with the pictures in:
The Thunderbolt display is a separate product, not an upgraded Mini DisplayPort display.
Both versions are still for sale by Apple
With the display connected, run System Profiler (or System Information) from the Utilities folder (in the Applications folder). Look in the Thunderbolt section. If the display were Thunderbolt it would show there.