Disk status commands return status on the current disk in the opened unit.
These commands may be done with quick I/O and thus may be called within
interrupt handlers (such as the trackdisk disk change handler). See the
"exec: device input/output" chapter of the amiga rom kernel reference
Manual: Libraries for more detailed information on quick I/O.

 determining the presence of a disk 
 determining the write-protect status of a disk 
 determining the drive type 
 determining the number of tracks of a drive 
 determining the current diskchange number