How Floppies Work
3 ½ drives, like other floppy disks, are a magnetic storage medium. The disk is kept between two sheets of thin, rigid plastic—hardly floppy at all, unlike previous versions of the floppy disk. The 3 ½ inch floppy disk is roughly square, though actually slightly rectangular, with a number of indents, cutouts and arrows that make sure that it can't be inserted incorrectly into the drive.
There is a hole in the middle around which the disk spins. Before any reading or writing goes on, the write protection status of the floppy drive is detected by checking whether a certain hole in the floppy disk is covered. Similarly, there is another hole indicating the density of the floppy disks—more on that later. Conveniently enough, these holes are exactly the same distance apart as the holes in a ring binder, meaning that they could easily be clipped in.
As the disk is spun, a head in the corresponding floppy drive would detect the magnetism of the floppy disk in the various sectors and thus reading the data. Data could be stored at a variety of densities, though there were two main ones for 3 ½ floppy disks: high density (HD) and double density (DD). Different densities were only partially compatible with each other since, if there was any mismatch between the magnetic head and the disk, data loss was quite likely.
The floppy disk had a spring loaded ejection, which meant that floppy disk removal could be forced with relative ease, unlike with today's CDs.