The floppy disk format is a thin, circular and flexible magnetic disk that can store digital information. The floppy disc structure consists of two principal layers. Most of the thickness of the disk is due to the base which is made of polyester plastic. On both sides of the polyester plastic substrate is a thin magnetic coating or binder layer. The magnetic coating binder is a polymeric material that contains magnetic oxide and some other additives such as lubricants.
It is the magnetic oxide that holds a magnetic signal and is where the digital information is stored. Finally, because in the floppy disk format the magnetic heads of the floppy drive are in contact with the disk surface when the disk is read or written, a lubricant is added to the binder surface. This lubricant layer acts to reduce friction and wear of the binder material and the magnetic heads in the drive.
For the 8 and 5.25 inch formats, a circular hole of about 2.5 cm or one inch in diameter is cut in the center. The hole is present so that the disk can fit firmly in the drive platter so that the disk can be spun. For the 3.5 inch disk, the hole has a metal hub glued onto the disk and thus, it sits a little different in the drive than the other floppy diskette formats.
Floppy disks are not used as bare disks. They are housed in flexible vinyl jackets for the 8 and 5.25 inch formats and in a rigid plastic jacket for the 3.5 inch format. The vinyl jackets have openings so that the diskettes can be read, whereas the rigid plastic jacket has a sliding gate that opens in the drive to expose the magnetic floppy disk surfaces. The vinyl jackets have a notch on the side. This is the write-protect tab and as long as the notch is present, information can be written to or erased from the disk. To prevent additional writing on the disk or files from being erased, a piece of tape can be used to cover the write-protect tab. For 3.5 inch floppy disks, the plastic jacket has a little plastic piece that you can slide up or down in order to move the disk from a non-write protected state to a write protected state.