From the programmer’s point of view, a PAR parameter is a communication channel between an application and the outside world. In a traditional application you would probably use Fortran input-output statements to prompt the user, or read from a text file for the additional data needed by your programme. The concept of a PAR parameter is similar to this, but instead of passing the information through a logical-unit number, PAR uses a named communication channel. This has advantages over normal methods. A name is more memorable both to the user and to the programmer, especially if it describes the parameter’s function. PAR also allows more sophisticated ways of controlling the behaviour of an application than the traditional Fortran I/O, and performs data-type conversion automatically.