All magnetic Disks are round platters. They come in different sizes, use different types of packing, and are made of rigid metal or flexible plastic. Based on these differences, there are many types of magnetic disks available today. However, all of them are classified broadly into two types-floppy disks. Floppy disks are packaged individually in protective envelopes or plastic cases, whereas hard disks are packaged individually or in multiples in cartridges or contamination-free containers. Depending on the type of packaging, hard disks are classified further into Zip/ Bernoulli disks, disk packs, and Winchester disks.
A floppy disk is a flat, circular piece of flexible plastic coated with magnetic oxide. It is encased in a square plastic or vinyl jacket cover. The jacket gives handling protection to disk surface. Moreover, it has a special liner that provides a wiping action to remove dust particles, which are harmful to disk surface and read/write head. Floppy disks are called because they are made of flexible plastic plates (not hard plates) that can bend. They are also known as floppies or diskettes. IBM introduced them in 1972. Until recently, they were one of the most popular and inexpensive portable secondary storage medium used in small computer systems. Two popularly used sizes of floppy disks were 3(1/2)-inch and 5(1/2)-inch. However, portable hard disk, optical, and pen drive have now replaced them because these storage devices outperformed floppy disk in storage capacity, access speed, and reliability.
Hard disks are the primary on-line secondary storage device for most computer systems today. They are made of rigid metal (frequently aluminum) platters and come in many sizes ranging from 1 to 14-inch diameter. Most commonly used sizes are 1.0-inch, 2.5-inch, and 3.5-inch.