Storage Devices of the Computer

Storage devices are used to store data and programs permanently. These devices are used to store large volume of data and program. Storage devices are also called backing storage devices, secondary storage devices, or auxiliary storage devices. Two important instructions or information from storage medium to memory. Writing is a process of coping the data, instructions or information from memory to a storage medium.

Types of Storage Devices
Different types of storage devices are as follows:

1. Magnetic Tape
Magnetic tape is a flexible plastic tape coated with magnetic material. It is widely used when large amount of  data  is to be processed sequentially. An advantage of magnetic tape is that it is very cheap and economical storage medium. Its major disadvantage is that it is very slow and it is only sequential.

2. Magnetic Disk

Magnetic disk is the most widely used storage media. A magnetic disk is a thin, circular metal plate / platter coated with magnetic material. Information can be recorded on or read  from the magnetic surface. A disk must be formatted before it can be used. The formatting process prepares the disk so that it can store data. Formatting process creates tracks and sectors on disk. Each track on a disk is divided into sectors. Each sector  holds a specific number  of characters. A sector is the smallest physical storage unit on a disk. Its size is normally 512 bytes. The magnetic disk is a random access storage media. It means that any part of the disk is directly accessible.

Types of Magnetic Disk
Different types of magnetic disks are as follows:


a. Floppy disk or Diskette                            

Floppy disk is also called diskette. It consists of a thin plastic disk coated with magnetic material. This disk is enclosed in a plastic jacket. It  can store a small amount of data. Data access speed of floppy disk is slower than hard disk. It is inexpensive storage media. The standard size of floppy disk is 3  1/2 inch and its capacity is 1.44MB. The circular piece of plastic on 3  1/2 inch disk is enclosed in a shell. A piece of metal covers the reading and writing area. It is called shutter. When the disk is inserted into a disk drive, the shutter opens to read the stored data with floppy disk drive. The read / write head in floppy disk drive is used to read and write data on floppy disk.

b. Hard Disk

Hard disk is a type of magnetic disk. It is also called fixed disk  because it is fixed in the system unit. A hard disk  consists of several circular disks called platters sealed inside a container. The container contains a motor to rotate the disk. It also contains an access arm and read/write head to read and write data to the disk. The platters are used to store data. A platter in a hard disk is  from 320GB and more. It is much faster than floppy disks. The data stored on hard dis is safer than floppy disk. 

c. Zip Disk

Zip disk is a portable disk. It has more storage capacity than floppy disk. Its storage capacity is up to 1000 MB. Zip disk can be read / written by using Zip drive. It is used for taking the backup of large data.


Optical Disk

Optical disk uses laser technology to read and write data. The LASER stands for light Amplification through Stimulated Emission of Radiation. Laser beam writes on the surface by creating small pits (hole) in the disk.Optical drive reads data by focusing laser beam on the surface of the disk.A laser detects the presence of a pit.The presence of pit indicates 1and absence of pit indicates 0. Laser beam converts these pits into digital data.Optical disk storage capacity is from 600 MB to over 1 GB

Categories of Optical  Laser Disks:  

Different categories of laser disks are as follows: 

• CD-ROM:                                                                                                                                          

CD-ROM stands for compact disk read-only memory.The data stored on CD-ROM can only be read.It can cannot be deleted or changed.It is a portable storage device.It can be used to transfer data easily. It can store about 650MB of data . It is used to distribute new application software and games. Information can be stored on CD-ROM for many years.

• CD-R

CD-R stands for CD recordable. The user can write data on CD-R only once but can read it many times.The data written to CD-R cannot be erased.CD-R drives are known as CD burners and are typically used to create custom music CDs . The process of putting information on CD is burning the CD.CD-R is also called WORM(Write Once Read Many).

• CD-RW

CD-RW stands for compact disc rewritable.The user can write data on CD-RW many times by erasing the existing contents.Such disks are normally used for applications using large volumes of storage with little update activity.

• Digital Video Disk (DVD)

 DVD stands for Digital Video Disk.It is similar to CD-ROM. It uses a laser beam with short wave length. The short wave length reads smaller holes on the disk. Data storage capacity of the disk is increased if the hole size is small.So the storage capacity of DVD ROM is much greater than CD-ROM.It can store up to 17 GB of data.
Solid State Storage Devices
 The solid state storage devices or flash memory devices are unique among all storage devices.Some solid state storage devices are non volatile and some are volatile.These devices are portable and provide fast access to data.They use very little power.They are very useful to store data on mobile devices and transport data from once device to another.They are widely used in digital camera, MP3 music players, notebook computers and cell phones.
 Types of Solid State Storage Device

Different types of solid - state storage are as follows:
1.USB  F Lash DRIVE
 USB flash drive is also knows as pen drive or key chain drive. It provides much greater storage capacity than floppy disk or Zip disk.A flash drive can store 64 GB or more data.It can be plugged into any USB port. It is small and lightweight storage device. USB flash drive requires no card reader .The size of USB flash drive is similar to the size of highlighter.It is durable and can be carried on a key ring.

2.Flash Memory Cards.
Flash memory cards are widely used in PDA, digital  camera, cell phones and notebook computers. Generally, these card are not interchangeable.