Simply put, floppy drives/disks come in two different sizes which include: 5 1/4" and 3 1/2". These drives/disks can be double density or high density. The 3 1/2" also comes in extended density.

The high density floppy disks hold more data than the double density. Finally, new technologies has given us Zip and Jaz drives with much larger storage capacities than traditional floppy drives.