The lists
The Old Movie List runs to 1999, the Mid Movie List from 2000 to 2012 and the New Movie List from 2013 to 2026, as on the menu of the old TamilO! portal.
The eras
Two eras in the Old list, three in the Mid list and five in the New list.
The rule
The sixteen most voted Tamil films of each era on TMDB; all twenty before 1990.