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Nowadays, external hard disks are also available. They are small in size and can be
carried anywhere.

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2. CD-ROM : CD-ROM stands for ompact isc- ead nly emory.
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It is popularly known as CD . It is a thin circular disk with a reflective
metal coating. The diameter of a CD ranges from 10 cm to 30 cm. A
typical CD measures 4.7 inches in diameter. One CD can store 600 to
750 MB data on it.
Nowadays, we get two kinds of CDs. They are:

CD-R CD-R stands for Compact Disc-Recordable. In this type of CD, data once written
cannot be changed or deleted.

CD-RW CD-RW stands for Compact Disc-Rewritable. Data in this CD can be erased or
rewritten.

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3. DVD : DVD stands for igital ersatile isc or igital ideo isc. It
is very similar to a CD but can store much more data. It is an optical
disk storage device. Its capacity may range from 4.7 GB to 17 GB.
4. Pen drive : A pen drive is also known as a flash drive . It can be used
to store and transfer data from one computer to another. It can be
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connected to the USB ( niversal erial us) port of a computer. It
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can store a large amount of data like 1 GB, 2 GB or more.

5. Blu-ray disc : A Blu-ray disc is similar to a CD or a DVD in

appearance but it can hold up to 128 GB of data. It uses blue-violet
lasers to read and hold a large amount of data. A Blu-ray reader is
required to use a Blu-ray disc. It is mainly used for storing very high-
quality video files and video games that require large amount of
storage space.

6. Memory cards : A memory card is used to store data in various

electronic devices like mobile phones, digital cameras, mp3 players
and many other portable devices. It is small in size and can store up
to 32 GB of data. We can transfer the data stored in a memory card to
our computer.

Extra Bytes

Floppy disks and Zip disks are also examples of secondary storage devices.
They are outdated and not used now.

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