If I remember this from my mainframe days, the capacity is 2MB
unformatted and 1.44 mb of formatted data. I remember from the old IBM
3350 drives, a track could hold a max of 19069 bytes if you use one
sector per track. Each extra sector per track takes away some space for
"landing" zones. Fixed format drives (like floppies) have *lots* of
landing zone space. Add in track addressing and that's where the
difference in capacities goes.