How are data stored?

A storage device is anything which is used to store computer data. Floppy disks, hard disks, optical disks,
CDs and magnetic tapes are types of storage device.
Physical storage refers to how data are actually kept on the storage disk. The most commonly used medium for storage is magnetic storage. With magnetic storage the computer stores data on disks and tape by magnetising selected particles of an oxide-based surface coating. The two most popular types of magnetic storage media are hard disks and diskettes.

Hard drive or hard disk storage provides faster access to files than a diskette. It is the storage area within the computer itself, where megabytes of space are available to store bits of information. A hard disk platter is a flat, rigid disk made of aluminium or glass and coated with a magnetic oxide. A hard disk consists of one or more platters and their read-write heads. A read-write head is the device that reads the data from the disk platter into the computer. It also writes data onto the platters. Hard disk platters in microcomputers are typically 3½ inches (about 10 centimetres) in diameter: the same size as the circular mylar disk in a diskette. However, the storage capacity of a hard disk far exceeds that of a floppy disk. The access time of a hard disk is also significantly faster than a diskette. Like diskettes, hard disks provide random access to files by positioning the read-write head over the sector that contains the requested data.

Diskette is a small, removable, flexible mylar plastic disk covered with a thin layer of a magnetizable substance, onto which digital data can be recorded and stored. Diskettes are also called floppies. Although today’s microcomputers typically use 3½ inch (about 10 centimetre) disks, we may still find 5¼ inch (about 15 centimetre) disks that were popular many years ago. Finding a disk drive to read 5¼ inch disks may be very difficult. Diskettes are generally used for transporting or shipping data files or for making duplicate copies of data files for back-up purposes. The storage capacity of a diskette varies but is considerably smaller than that of a hard drive.
Other types of storage devices are:
Magnetic tape: It is a continuous plastic strip covered with magnetic oxide, the tape is divided into parallel tracks onto which data may be recorded by selectively magnetising parts of the surface, or spots, in each of the tracks. The data can then be stored and reused.
Back up: It is used to copy a computer files to another medium, usually on a diskette or magnetic tape, so that the data are safe in case the original file is damaged or lost. Backups are usually copied to storage devices that can be removed from the computer and kept separately from the original.
Optical disk: A storage device that uses reflecting surfaces and laser technology to read and write data on a disk is optical disk which is also known as a laser disk. Some types of optical disks are CD-ROM, CD-RW.