While there may seem to be a bewildering array of compilers to choose from on an IBM system, they can be simply categorized as follows. For example, there is really but a single fortran compiler on the system, and all the variants above reference this compiler albeit with different default options, libraries, etc. The differenct "compilers" are really just scripts that are intended as a convenience to logically group certain options together. The "77", "90" and "95" suffixes are used for programs conforming to the Fortrans 77, 90 and 95 standards, respectively. The "mp" prefix is for message passing code and will link to the MPI libraries. The "_r" suffix indicates reentrant code and is for IBM SMP programming (for example, OpenMP code). Similar observations apply to the C and C++ compilers as well. See the man pages, e.g. “man xlf”, or “cc –help” for further information.

The vendor supplied compilers are recommended. The GNU compilers (g77, gcc, g++) are provided for convenience and compatibility with certain packages.