Intel® Fortran Compiler 16.0 User and Reference Guide
In Fortran's I/O system, data is stored and transferred among files. All I/O data sources and destinations are considered files.
Devices such as the screen, keyboard, and printer are external files, as are data files stored on a device such as a disk.
Variables in memory can also act as a file on a disk and are typically used to convert ASCII representations of numbers to binary form. When variables are used in this way, they are called internal files.
For more information, see the individual topics in this section.