If you are opening an existing file, most file systems linked into the run time system are searched for the named file. If, however, you are creating a new file, you must tell the run time system which file system to use. You accomplish this with the following ACUCOBOL-GT runtime configuration file variable:
This variable designates the file system used for newly created files that are not individually assigned. If this variable is not given a value, the EXTFH file system is used.
means that all new files are be DB2 files unless individually assigned to another file system.
means that all new files are be Oracle files unless individually assigned to another file system.