The compiler creates an XFD for each indexed file in the compiled program when you specify the -Fx compile-time option. XFDs are fully portable, so no recompilation is necessary if you change hardware.
The compiler option -Fa causes the generation of XFDs for indexed, relative, and sequential files for use with international character mapping only.
The compiler option -F4 generates version 4 XFD files for backwards compatibility with older versions of the runtime.