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 most recent formal standard for the language was published in 1997 and is known as Fortran 95 . By 1965 , Fortran IV was supposed to be the `` standard '' and in compliance with American Standards Association X3 .4.3 FORTRAN Working Group .