Floppy Disk

The floppy disk, flexible disk, or diskette, was introduced in 1973 to replace punched cards as a medium for data entry, but it can also store programs and data files. Today, diskettes are produced in two sizes, 5¼ inches and 3½ inches. The term microfloppy disks is often used to refer to the 3½" diskettes. Floppy disks are made of plastic and coated with a magnetizable oxide substance. In most respects, they are miniature magnetic disks. Since the diskettes are relatively inexpensive (most sell for less than $1.00), they are popular for use with microcomputer systems and point-of-sale terminals. They are reusable, easy to store, and weigh less than two ounces. Floppy disks can even be mailed. In addition, they can add security to a computer system because they can be removed and stored in a safe place.

Data is stored on a floppy disk as magnetized spots in tracks, as on conventional magnetic disks, and elements are addressed by track number and sector number (see picture below).

The read/write head accesses the disk through the oblong or rectangular opening in the jacket, called the read/write notch (see picture below).

The head moves back and forth to read the data or write data to the disk. Unlike the one used in hard disk systems, this read/write head actually rides on the surface of the disk rather than being positioned slightly above it. The disk rotates at a speed of 360 revolutions per minute (as compared to as many as 5,000 revolutions per minute for hard disk drives).

Magnetic disks have several advantages over magnetic tapes:

• Disk files on magnetic disks can be organized sequentially and processed in the same way as magnetic tape, or they can be organized for direct-access processing.
• The fast access time offered by magnetic disk storage allows data files to be accessed or changed immediately.
• Quick response can be made to inquiries (normally, response is made in seconds).
• With the appropriate software, a single transaction can simultaneously update or change several files stored on disks.

The major disadvantages of magnetic disk storage include the following:

• Magnetic hard disks are a relatively expensive storage medium; their cost may be ten times that of magnetic tape in terms of cost per character stored. However, reductions in disk cost and the introduction of floppy disks are making these storage devices more affordable.
• When data stored on a disk is changed, the original data is erased and the new data is stored in its place. Therefore, magnetic disks do not provide backup files. Data can be lost if there are inadequate provisions for error checking and backup files.
• Disk storage requires more complicated programming to gain access to records and to update files. The technicians who maintain the complicated hardware must be highly skilled.
• The ease of gaining access to data stored on disk files can create security problems.

Last Updated April 19/99