A 3.5-inch diskette was first created by IBM in 1984 with an initial capacity of 720 KB and later 1.44 MB that replaces 5.25" diskettes. These disks were the most commonly used methods to backup and store data in the 1990s, but by 2000 were seldom used or found with the introduction of CD-R discs and later USB thumb drives.
The 3.5-Inch floppy diskettes have dimensions of 8.9cm in width by 9.3cm in height and are referred to as floppies because of the circular magnetic floppy within the hard shell. 3.5-inch floppy diskettes come in sizes of 720 KB low-density, 1.44 MB high density capacity, and IBM even developed an Extended Density disk capable of holding 2.88 MB. The picture is a diagram of a floppy diskette and each of its major components.
Write protect tab
In the diagram above, notice the small write protect tab. This tab enables the floppy disk to be switched from write-protected and unwrite-protected. Move the tab to the top position, creating a hole, makes the disk write protected. Moving the tab to the bottom position allows the disk to be un-write protected, which means the diskette can be written too, erased, or have information deleted from the diskette. Some cheaper disks may be missing this tab. To write information to the diskette you have to place a piece of scotch tape over the hole.
High Density hole
Second, the top-right hand of the back of the floppy you will notice a small hole. If the drive mechanism detects that this hole exists, the computer knows it is a High Density diskette.
Middle of disk
Third, the circular metal disk in the middle of the floppy diskette. This part is used to rotate the magnetic medium within the floppy disk casing.
Read / Write access door
Finally, there is a metal door that can be moved left and then will snap back to its original position. This door is used to allow the read/write head within the floppy drive to have the capability of accessing the magnetic medium within the casing. Once the diskette is removed, this door will snap back into position, helping to prevent anything from getting on the magnetic medium and destroying it. This also makes these types of diskettes more reliable than the earlier 5.25" diskettes.
As seen in the picture below of a clear 3.5" floppy diskette there is a circular cloth that is located on both sides of the floppy; this cloth helps clean and protect the magnetic disk within the diskette.