The XL Fortran compiler helps you to port or to migrate source code among Fortran compilers by providing full Fortran 90 and Fortran 95 language support and selected language extensions (intrinsic functions, data types, and so on) from many different compiler vendors. Throughout this book, we will refer to these extensions as "industry extensions".
To protect your investment in FORTRAN 77 source code, you can easily invoke the compiler with a set of defaults that provide backward compatibility with earlier versions of XL Fortran. The xlf, xlf_r, xlf_r7, f77, and fort77 commands provide maximum compatibility with existing FORTRAN 77 programs. The default options provided with the xlf90, xlf90_r, and xlf90_r7 commands give access to the full range of Fortran 90 language features. The default options provided with the xlf95, xlf95_r, and xlf95_r7 commands give access to the full range of Fortran 95 language features.
To protect your investments in FORTRAN 77 object code, you can link Fortran 90 and Fortran 95 programs with existing FORTRAN 77 object modules and libraries. See Linking New Objects with Existing Ones for details.