from a personal computer point of view there there only 3 sizes of floppy disk in common use: 8", 5.25" and 3.5". smaller sized floppy disks emerged late in the game which got used for things like music players and cameras. but these formats never found a foot hold in computing. almost everything about a floppy disk is the same no matter how large they were. disks use physical detections for practically everything: read/write capable, track zero detection, and sometimes sector position. 3.5" drives had density detectors. this meant the the floppy inside the drive define how it was read. you can see how easily a drive could become "out of alignment" making media impossible to read in other drives.