program TEST ! column 73 ! | write(*,*) & & ' test ' end ! | ! column 6This is really not standard Fortran 77 since neither "&" nor "!" are in the standardized character set. On the other hand, these constructs are perfect for program segments that are to be included in Fortran 90 program units using the INCLUDE statement (refer to Appendix 3, section 1), sometimes using the old form and sometimes using the new form of the source code. The program segment is then supposed to be written as if blanks were significant.
Comments are an incompatibility problem between Fortran 77 and Fortran 90, but of course not between fixed and free forms of Fortran 90 since the "!" is permitted in both. The exclamation mark is also permitted in Sun and DEC Fortran 77 (both DEC Station ULTRIX and VAX VMS), the Cray compiler CF77, and the Absoft Fortran 77 compiler.
Another important condition is of course that the program really obeys the standard.