In VMS, null devices have the names "NL:", "_NL:", "NLA0:", and "_NLA0:". A null device fulfills every input request by returning a null string and setting $ZEOF. A null device discards all output. GT.M maintains a virtual cursor position for null devices as it does for terminals. Use null devices for program testing and debugging, or for jobs that permit I/O to be discarded under certain circumstances. For example, JOB processes must have input and output devices associated with them, even though they do not use them. Null devices are low overhead never-fail alternatives.