how do i make IA64 the default compiler in VS2013 while compiling Fortran programs ?
vs2013 doesn't support ia64 (Itanium) development. Microsoft discontinued support for Itanium about the time Intel introduced Intel64 Nehalem.
If you mean you want a new project to default to x64, there's a discussion at
For more complete information about compiler optimizations, see our Optimization Notice.