Games : Do Pokemon Fire Red/Leaf Green use the new or the old EV/IV calculations?

A friend who got me into Pokémon told me about EV and IV's. He was saying how Pokémon R/B/Y and G/S/C have a different IV formula then the generations after that.

But do FR/LG and HG/SS go by the newer IV formula or the original one?

Also wondering is someone could maybe explain the process a little better than he did and can suggest a calculator.