g77 offers an ever-widening set of intrinsics. Currently these all are procedures (functions and subroutines).
Some of these intrinsics are unimplemented, but their names reserved to reduce future problems with existing code as they are implemented. Others are implemented as part of the GNU Fortran language, while yet others are provided for compatibility with other dialects of Fortran but are not part of the GNU Fortran language.
To manage these distinctions, g77 provides intrinsic groups, a facility that is simply an extension of the intrinsic groups provided by the GNU Fortran language.