n is either 1 (true) or 0 (false). The default value is 0.
OpenMode specifies the default read/write mode to use when opening sequential files with the OPEN command. The options are Read-Write (1) or Read (0).
Changing This Parameter
On the Compatibility page of the Management Portal (System Administration > Configuration > Additional Settings > Compatibility), in the OpenMode row, click Edit. Choose a mode, Read (0) or Read-Write (1).
Instead of using the Management Portal, you can change OpenMode in the Config.Miscellanous class (as described in the class reference) or by editing the CPF in a text editor (as described in the Editing the Active CPF section of the “Introduction to the Configuration Parameter File” chapter in this book).