Diskettes, or floppy disks, are small, round platters encased in a plastic jacket. The platters are made of a tough Mylar plastic and coated with a magnetizable substance.
As in the case of hard disks, each side of the diskette contains concentric tracks, which are encoded with 0 and 1 bits when you write data and programs to them. The jacket is lined with a soft material that wipes the disk clean as it spins.
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Unlike their counterparts in hard-disk systems, read/write heads touch a diskette’s surface. Also, while hard disks often spin continuously even when not in use, a diskette spins only when a read or write command is issued to its drive.
Both of these facts, as well as their removability and flexible surface, account for the diskette’s relatively slow rate of speed (400 to 600 rpm) and lengthy access time.
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Types of Diskettes :
There are dozens of types of diskettes commercially available. If one were to cite a single properly, however, that most distinguishes one of these products from another, that property would likely be size.
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Diskettes are widely available in three sizes (diameters)- 3.5 inches, 5.25 inches, and 8 inches. Historically, the 8-inch diskettes came along first, then respectively, their 5.25 inch and 3.5 inch counterparts.
The 8 inch and 5.25 inch diskettes are encased in flexible, plastic-coated cardboard jackets, whereas the 3.5 inch diskettes are contained in rugged plastic cases that can fit into a shirt pocket.
Eight-inch diskettes are more commonly used with small minicomputers and 5.25 inch and 3.5 inch sizes with microcomputer systems. Strange as it may seem, 3.5 inch diskettes can store more data than 5.25 inch ones.
Despite their small size, diskettes can store a respectable amount of data. Common capacities are 360 kilobytes for 5.25 inch diskettes and 720 kilobytes, 800 kilobytes, or 1.44 megabytes for 3.5 inch diskettes.
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A 360 kilobyte diskette can store over 100 typewritten pages of information; thus, 3.5 inch diskettes can store about 400 pages. Mega floppies- diskettes that can carry 2, 4, or 10 megabytes of data- are also available, although not commonly found in practice.
It is highly possible that the next generation of microcomputers will use a mega floppy format.
To protect data, diskettes also contain a write-protect notch or square. This prevents the user from accidentally writing on the disk. Covering the notch on 5.25 inch diskettes makes it impossible to write on the surface.
The convention on 3.5 inch and 8 inch diskettes is the opposite: Exposing the notch or square makes writing impossible.