what is the exact differnce between nAttai and gambira nAttai?for someone once told me that they are actually the same raaga but some ppl like to call it as gambira nAttai while others prefer the former.

thanks in advance!!!

Gambira Nattai and Nattai are not the same. They are both janya ragas derived from chalanattai(melakartha).
Gambhira Nattai - S G3 M1 P N3 S, S N P M G S
Nattai - S R3 G3 M1 P D3 N3 S, S N3 P M1 R3 S