Storage Devices

                              

 

Storage Devices

Storage devices are used to store data and instructions permanently. Storage devices are also called secondary storage devices / backing storage devices / external storage devices or auxiliary storage devices. Examples of storage devices include Hard Disk, CD and DVD etc.

Why Secondary Storage Devices are Used?

Secondary storage devices are used because:

1. Primary memory(RAM) is volatile and temporary. When computer is switched off, all data in ram is erased.
2. Storage devices can store large amounts of data and instructions permanently whereas Primary memory has less capacity of storing data.

Types Of Storage Devices

There are three main types of storage devices:

1. Magnetic Tape 2. Magnetic Disk 3. Optical Disk

1. Magnetic Tape



Magnetic tape is the oldest storage device. It is made of plastic coated with magnetic material. Data is stored on magnetic tape in the form of magnetic spots. Tape drive is used to read and write data on tape. Magnetic disk is sequential access device. It is slower device than magnetic disk or optical disk. Magnetic tapes are used in reels of different lengths, for example 200, 600, 1200 feet etc.

2. Magnetic Disk

A magnetic disk is a thin circular metal or plastic disk coated with magnetic material. Data is stored in the form of magnetic spots. Magnetic disk is random access device. It is faster than magnetic tape. There are three main types of magnetic disk:
a. Hard Disk b. Floppy Disk c. Zip Disk


a. Hard Disk

The hard disk is also called fixed disk. It consists of one or more metal plates. The plates are fixed in the drive. Metal plates are coated with magnetic material to store data. A motor rotates disks. There is also an access arm and read / write heads to read and write data on disks.
Following are major characteristics of hard disk:
- The storage capacity of hard disk is much greater than floppy disk.
- Now a days hard disks of size 40 GB, 80 GB or more are available.
- Hard disk is covered in a hard jacket and there are less chances of disk damage due to dust and mishandling.
- Now days Operating system and application programs are installed on hard disk.
- Before using a magnetic disk we use operating system to format the disk. Operating system divides the disk into circles called tracks. Each track is divided into pie-shaped areas called sectors. Data is stored in sectors. Each sector can store 512 bytes.

b. Floppy Disk

Floppy disk is a small plastic plate coated with magnetic material. Data is stored in magnetic spots. Main advantage of floppy disk is that it is used to transfer data from one computer to another. Floppy disk drive is used to read and write data on floppy disk.
Floppy disk is available in two sizes:
· 3 ½ INCH Floppy Disk
It is also called micro floppy disk. Its diameter is 3½ inch. It is covered in a hard plastic cover. Read/Write window is covered with a metal shutter. When disk is inserted into disk drive then shutter is automatically opened. It can be write protected by a notch. Storage capacity of micro floppy is 1.44 MB.
· 5¼ Inch floppy disk.
It is a 5¼ inch diameter plastic plate coated with magnetic material. Its storage capacity is 1.2 MB. It is not used in modern computers.

c. Zip Disk

Zip disk is similar to 3 ½ inch floppy disk. But it can store 100 MB or more data. Zip disk drive is used to read and write data on a zip disk.

3. Optical Disk

LASER technology is used to read and write data on Optical disk. LASER stands for Light Amplification through Emission of Radiation. Laser beam writes on the surface of optical disk by creating very small holes. The presence of hole represents a One and absence of the hole represents a Zero. There are following main types of optical disk.
1.CD-ROM, 2. CD-R or WORM, 3. CD-RW
4.DVD-ROM, 5. DVD-R, 6. DVD-RW

 1. CD-ROM



CD-ROM stands for Compact Disk-Read Only Memory. The data stored on Cd-Rom can only be read. It cannot be deleted or changed. It is a portable storage device. Data can be easily transferred by CD Rom from one computer to another. Commonly it can store 650 MB / 700 MB/ 750 MB data. It is used to store large amounts of data like Software or audio/video data.We purchase Software, movies, dramas, lectures, books, wallpapers and other data on Cd-Rom.

2. CD-R (CD Recordable) Or WORM (Write Once Read Many)

CD-R stands for Compact Disk -Recordable. Initially, it is a blank disk. User can store data on it only once. This is why it is also called WORM(Write Once Read Many) disk too. Because we can write data on it only once and later we can read many times. The devices to store data on CD-R are called CD Writers or CD Burners. We can write data on CD-R only once, but can read data many times. Because of this write once read many quality, CD-R is often known as WORM(write once read many).

3. CD-RW ( CD Rewritable )

CD-RW stands for Compact Disk Rewritable. This is a special type of CD. User can write data on it, if there is an error in writing data, he may erase the contents and rewrite again. CD-Writers are used to store data on CD-RW.

4. DVD - Digital Video Disk (DVD-ROM)

DVD stands for Digital Video Disk. A laser beam with a short wave length is used to create very very small holes on the surface of disk. So there are much more tiny holes on the surface of DVD as compared to that of CD. Therefore, storage capacity of DVD is much larger than CD. It can store up to 17 GB or more data. DVD-ROM is pre recorded and it can contain data like movies, videos and software etc. User cannot change or delete data from DVD-ROM. It is read only.
5. DVD-R (DVD-Recordable)

DVD-R stands for Digital Video Disk Recordable. Initially it is a blank disk. User can store data on disk only once. Then it becomes read only. It is normally used to store high definition video movies. DVD-Writers are used to store data on DVD-R.

6. DVD-RW ( DVD Rewritable)

DVD-RW stands for Digital Video Disk Rewritable. User can write data on disk many times by erasing the old data.

What is CD?

CD stands for Compact Disc. Compact Disk or CD is a popular storage device. It is a portable storage device. It can store about 700 MB (Mega Bytes) of data.

Advantages of Compact Disk

• It can store large amounts of different types of data. It can store information in the form of sound, videos, programs or software, pictures and other graphics, documents and many more formats of data.

• We purchase games and software stored on CDs. CD can store audio/ video songs and videos, too.

• It is very inexpensive way of storing large amounts of data permanently.

• It is used for backing up of important data, that can be recovered in future if any data is lost from our PC's hard disk.

• Compact Disks are easy to use and easy to carry.

• Compact Disks are durable and reliable. CDs can store data for many years without losing a single byte.

Different Types of Compact CDs are:

CD-ROM (Compact Disk Read Only Memory)

CD-ROM comes with already stored data on it, like games or software. As the name CD-ROM says, data can not be deleted or edited on CD-ROM. We can only read or copy data from CD-ROM.

CD-R (Compact Disk Recordable)

Compact Disc Recordable is a blank disk. We can store data on it with the help of CD-Writer only once. Then it becomes CD-ROM. So, we can only read data. We cannot change or delete data.

CD-RW ( Compact Disk Rewritable)

CD-RW disk is more useful type of Compact Disk. We can write data on CD-RW many times. We can read data, write data, erase data and rewrite data on CD-RW for many times.

What is DVD?

DVD stands for Digital Video Disk or Digital Versatile Disk. The basic difference between CD and DVD is that DVD has much more data storage capacity. DVD can store data up to 17 GB (Giga Bytes).

Advantages of DVD

• DVD can store much more larger amounts of different types of data as compared to CD. It is used to store HD movies. It can store information in the form of sound, videos, programs or software, pictures and other graphics, documents and many more formats of data.

• We purchase high quality movies, games and software stored on DVDs.

• It is very inexpensive way of storing large amounts of data permanently. Although it is more expensive than CD but it can store much more data.

• It is used for backing up of important data, that can be recovered in future if any data is lost from our PC's hard disk.

• DVDs are easy to use and easy to carry.

• DVDs are durable and reliable. DVDs can store data for many years without losing a single byte.

Different Types of DVDs are:

DVD-ROM (Digital Video Disk Read Only Memory)

DVD-ROM comes with already stored data on it, like movies, games or software. As the name DVD-ROM says, data can not be deleted or edited on DVD-ROM. We can only read or copy data from DVD-ROM.

DVD-R (Digital Video Disk Recordable)

Digital Video Disc Recordable is a blank disk. We can store data on it with the help of DVD-Writer only once. Then it becomes DVD-ROM. So, we can only read data. We cannot change or delete data.

DVD-RW ( Digital Video Disk Rewritable)

DVD-RW disk is more useful type of DVD. We can write data on DVD-RW many times. We can read data, write data, erase data and rewrite data on DVD-RW for many times.

Here we tabulate the main differences between CD and DVD.

Sr. No	CD	DVD
1	It stands for Compact Disk	It stands for Diital Video Disk or Digital Versatile Disk.
2	CD can store about 700 MB of data. So, data storage capacity is much smaller than that of DVD.	DVD can store about 17 GB data. Therefore, data storage capacity is much larger than that of CD.
3	Technology to read/write on CD uses a laser beam of larger wave length that makes larger pits (tiny holes) on CD. Each pit represents a binary 1.	Technology to read/write on DVD uses a laser beam of shorter wave length that makes smaller pits (tiny holes) on DVD. Each pit represents a binary 1. Therefore, there will be more pits on DVD surface than that of CD. So there will be more data storage capacity of DVD than that of CD.
4	CD is cheaper than DVD.	DVD is more expensive than CD.
5	CD has slower data transfer rates.	DVD has faster data transfer rates.
6	Different types of CD include: CD-ROM, CD-R and CD-RW.	Different Types of DVD are: DVD-ROM, DVD-R and DVD-RW.