Several revisions of the language have appeared , including the very well known FORTRAN IV ( the same as FORTRAN 66 ) , FORTRAN 77 and Fortran 90 . The FORTRAN defined by the first standard became known as FORTRAN 66 ( although many continued to refer to it as FORTRAN IV , the language upon which the standard was largely based ) . FORTRAN 66 effectively became the first `` industry-standard '' version of FORTRAN .