DEFAULT_FILESYSTEM specifies the default file system to be used for all file I/O. The default value is Vision. If you want to use HP COBOL's MPE file system instead, add the following to the cblconfig file:
DEFAULT_FILESYSTEM MPE
This tells the runtime to use KSAM files instead of Vision files. If you specify Vision, the relative and sequential files will be in bytestream format instead of MPE format.