DEFAULT-HOST* - When the application program is opening an existing file or creating a new file, you need to tell the runtime which file system to use. You accomplish this with one of two configuration variables: DEFAULT-HOST or filename-HOST.
DEFAULT-HOST filesystem
designates the file system to be used for files which are not individually assigned. If this variable is not given a value, and if you have not individually assigned a file system (with filename-HOST), then the Vision file system is used.