Some question about forcefield.

Hi, What‘s the difference between CHARMm and Academic charmm (19/22/27/36), I kown CHARMm is the commercial version of charmm, a general-purpose all-atom forcefield with a wide coverage for proteins, nucleic acids and general organic molecules.however I can't figure out what the difference between them. Does CHARMm contains charmm 36? And how do you select them when running molecular dynamics?