FORTRAN-20 is a FORTRAN compiler for TOPS-20. It supports the FORTRAN-77 standard (ANSI X3.9-1978 American National Standard Programming Language FORTRAN) with extensions and additions.

!2345+---^---------^---------^---------^---------^---------^---------^--........
      program hello
      write(5,*) ' Hello, World!'
      stop
      end

Digital Equipment Corporation. (1987, February). AA-N383B-TK FORTRAN Language Manual [Online]. Available: http://bitsavers.trailing-edge.com/pdf/dec/pdp10/TOPS20/fortran/AA-N383B-TK_FORTRAN_Language_Manual_Ver_10_May85.pdf.

P. H. Hargrove, S. T. Whitlock, E. Boman. (1997, December). Fortran 77 Tutorial [Online]. Available: http://www.stanford.edu/class/me200c/tutorial_77.