Perhaps the formatted capacity, or the safe capacity, but I can specifically recall being able to format those same floppies up to... I forget, maybe ~2MB? Something like that.
Yeah, the unformatted capacities of 3.5” floppy disks were:
SS-DD - 512KB
DS-DD - 1MB
HD - 2MB
ED - 4MB
LS (floptical) - 21MB
Technically you could format some of the lower density media in the high density drives and get the expanded capacity (although you may have needed to modify the media a little - holepunch to make an HD drive see a DS-DD disc as “HD”), although it wasn’t always very reliable and depended on the physical media and the capabilities of the individual drives.
Different file systems used the 2*80 tracks differently, hence the different formatted capacity, DOS usually had the lowest, Macintosh in the middle, Amiga had the most (although the Amiga HD floppies were a bit of a cludge - the drive spun at half speed due to a limitation of the Amiga floppy controller, which was also the reason you couldn’t just use a “PC” HD floppy in an Amiga without modification).
Same with older floppy disk formats. Using FAT16 (or FAT12 on some systems) you can often format DD 3.5" disks to 830K instead of the usual 720K. On the Amiga the same disks are usually 880K.
