As an option, you can specify the record length in your high-level language program.
The system needs to know the length of the record your program will be processing, but it is not required that you specify the record length in your program. The system automatically determines this information from the attributes and description of the file named in your program.
If the file that is opened contains records that are longer than the length specified in the program, the system allocates a storage area to match the file member's record length and this option is ignored. In this case, the entire record is passed to the program. (However, some high-level languages allow you to access only that portion of the record defined by the record length specified in the program.) If the file that is opened contains records that are less than the length specified in the program, the system allocates a storage area for the program-specified record length. The program can use the extra storage space, but only the record lengths defined for the file member are used for input/output operations.