2.1.2.3 Preconnected or Implicitly Named Units

Three unit numbers are automatically associated with specific standard I/O files at the start of program execution. These preconnected units are standard input, standard output, and standard error:

• Standard input is logical unit 5

• Standard output is logical unit 6

• Standard error is logical unit 0

Typically, standard input receives input from the workstation keyboard; standard output and standard error display output on the workstation screen.

In all other cases where a logical unit number but no FILE= name is specified on an OPEN statement, a file is opened with a name of the form fort.n, where n is the logical unit number.