- 184/$B8 holds the file number.
- 185/$B9 holds the secondary address.
- 186/$BA holds the device number.
The SETLFS routine in KERNAL for setting up these parameters, simply "dumps" the values handed to it into addresses 184 thru 186. BASIC's OPEN command uses this routine, but machine code programmers are free to write the required information directly into these addresses instead of calling SETLFS.