The GNU Fortran language includes a number of features that are part of Fortran 90, even when the -ff90 option is not specified. The features enabled by -ff90 are intended to be those that, when -ff90 is not specified, would have another meaning to g77—usually meaning something invalid in the GNU Fortran language.
So, the purpose of -ff90 is not to specify whether g77 is to gratuitously reject Fortran 90 constructs. The -pedantic option specified with -fno-f90 is intended to do that, although its implementation is certainly incomplete at this point.
When -ff90 is specified:
COMPLEXtype, is the same type as the real part of expr.
For example, assuming `Z' is type
`REAL(Z)' would return a value of type
not of type
REAL(KIND=1), since -ff90 is specified.