"I/O path" is a data type. Other data types are integer, long, real, complex and string. An I/O path is implicitly declared whenever you use it in a program. It must be initialized with the ASSIGN statement before it is used. Input and Output statements use an I/O path to specify the entity (device, file, pipe, buffer, etc.) that the computer communicates with during the I/O operation. When an input/output statement does not explicitly involve an I/O path, one is created internally, used for the duration of the statement and then discarded.
