what is floppy disk

The principal advantage of the floppy disk, or diskette, over the magnetic tape, cassette or cartridge is that the disk can be accessed directly. Any item of data or program stored on it can be accessed without accessing information stored previously. Floppy disk consists of a piece of magnetically coated Mylar enclosed in a plastic or cardboard jacket. Floppy disks are generally available in either a 5.25 inch diameter or a 3.5 inch floppy diskette. The 5.25 inch diameter floppy disk, is sometimes referred to as a mini-floppy. The 3.5 inch disk is called a micro-floppy. Other than their outward appearance they are very similar.

The floppy disk is held in the center of a disk drive by a motor-driven shaft that spins the disk within its protective jacket at 300 to 360 rotations per minute (Figure 5.2). Data are read from or written onto the disk by a read/write head. This head moves in or out over the head access slot in the jacket to access different tracks on the surface of the disk.

Like the magnetic tape cassettes, floppy disks can also be file protected.

Floppy disks are organized into sides, tracks, and sectors referred to as the format are used with 3.5 and 5.25 inch diskettes. The surface of some micro diskettes are subdivided into 80 concentric circular areas or tracks and each track is divided onto 9 or 18 pie-shaped segments or sectors. Each sector contains two fields: i) a sector address field containing track, side, and sector numbers etc. and ii) the data field containing the user data.

A number of steps are followed to access an item of data from a specific track and sector. The average access time for this process for soft sectored mini-floppy is generally around 200 milliseconds. But this is slow when compared to access times on the microsecond and nanosecond range for RAM storage devices, but quite fast compared to the sequential access with cassettes.

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