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5.25" Media Construction
The first floppy disks were actually not 3.5" or 5.25" at all--they were 8" in size. (And what beasts they are, if you've ever seen them. They are still in use on some very old non-PC equipment.) The 5.25" is the younger cousin of the original floppy and retains, for the mostpart the same basic design as that media, in a smaller size.
The 5.25" disk is comprised of two basic pieces: the actual, round disk media, sometimes called a "cookie", and the protective jacket. The actual disk is made from a thin piece of plastic and is coated with a magnetic material. It has a large hole in its center that is used by the drive to grasp the disk and spin it--the jacket of course does not spin. A slot is cut in the jacket to expose the disk for the read/write heads; it is wide enough for the heads and long enough to allow the actuator to move the heads over all of the tracks on the disk. A notch at the side of the disk acts as a write-protect control; it is somewhat crude however in that you must use tape over the notch to write-protect the disk.
The 5.25" disk earns its name: "floppy". These disks are notoriously fragile. The jacket provides inadequate protection for the disk itself; this, combined with the large size of the disk, makes it very easy to bend. Special care must be taken not to damage them accidentally; basically, they need to be kept inside a plastic box most of the time to avoid destroying them. They do not take kindly to being sent in the mail unless in a larger box. The read/write "window" of the disk is exposed and for this reason the disks can be easily damaged if not kept in their protective paper "pockets". They can even be damaged by writing on the jacket with a ball-point pen, because the jacket is so thin that the pen can cause an impression in the disk media itself.
The lack of durability of the 5.25" media helped contribute to the downfall of the 5.25" floppy disk drive, compared to the 3.5" disks.
Next: 3.5" Media Construction