Magnetic Tape:Magnetic tapes are used for large computers like mainframe computers where large volume of data is stored for a longer time. The cost of storing data in tapes is inexpensive. Tapes consist of magnetic materials that store data permanently. It can be 12.5 mm to 25 mm wide plastic film-type and 500 meter to 1200 meter long which is coated with magnetic material. 

Optical Disk:

Optical disks can be divided into the following categories:
Compact Disk/ Read Only Memory (CD-ROM)
Write Once, Read Many (WORM)
Erasable Optical Disk

Magnetic Disk:
A Circular disk coated with magnetic material rotates at a very high speed inside the computer drive. Data is stored on both surfaces of the disk. Magnetic disks are most popular for the direct access storage device. Each disk consists of a number of tracks. Information is recorded on tracks of a disk surface in the form of tiny magnetic spots. The presence of a magnetic spot represents one bit and its absence represents zero bit. The information stored in a disk can be read many times without affecting the stored data. 

Flash Memory

Flash memory is a type of Electronically-Erasable Programmable Read-Only Memory (EEPROM).
Flash memory is non-volatile (like ROM) but the data stored in it can also be erased or changed (like RAM).

Solid State Architecture

Future Molecule Storage using Nano Technology