• RSI only support calls to C on most platforms
  
  
• RSI support Fortran on some platforms (eg Solaris)
  
  
• RSI did not know how to interface VC++ with DVF
  
  
• RSI supply a standard routine called CALL_EXTERNAL for this purpose
  
  
• CALL_EXTERNAL ensures that a IDL is portable at the source code level from one platform to another
  
  
• There is a wide range of alternative implementations of CALL_EXTERNAL for platforms such as IRIX, AIX, Linux
  
  
• RSI were helpful and interested in what we were doing