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Hard disks are available in a variety of sizes with storage capacities
                                       as high as 5 TB (TeraByte) or even more. The CPU can access data
                                       stored on a hard disk much faster than it can access data on a CD.

                                       External hard disks are also available. They are the hard disks that can
                                       be connected to any computer with the help of a USB port.
                 External hard disk


                    Info Byte

                     First hard disk was introduced by Seagate in 1979 which could hold 5 MB data.


                 Optical Disc

                 An optical disc is an electronic data storage medium that can be used to write and read
                 using a low-powered laser beam.

                 Compact Disc (CD)

                 Compact Disc (CD) is an external storage device. It can hold upto 700
                 MB of data. The CD drive reads information stored on a compact disc.
                 CD  drive  is  usually  connected  inside  the  CPU  box  but  can  also  be
                 connected using a USB port.
                                                                                                           CD
                 Types of CDs:
                 1.   CD-ROM (Compact Disc Read Only Memory): A CD-ROM is a CD containing data

                    that has been written at the time of manufacturing. The data cannot be modified or
                    erased.

                 2.   CD-R (Compact Disc Recordable): A CD-R can be used to write data by the user only
                    once. This data cannot be changed or erased.
                 3.   CD-RW (Compact Disc Rewritable): A CD-RW can be used to write data again and
                    again. The data can be erased and modified as many times as required.


                                     Digital Versatile Disc or Digital Video Disc (DVD)
                                     The DVD is almost similar to a CD, even the working is also similar.
                                     The only difference is that it can hold more information than a CD.
                                     DVDs are widely used for storing and viewing movies and other
                                     data.
                       DVD

                 Blu-Ray Disc

                 Blu-ray disc is an optical disc. It is used for storing a large amount
                 of data. The main difference between DVDs and Blu-ray discs is that
                 storage capacity of blue-ray disc is higher than that of a DVD.
                                                                                                      Blu-ray disc





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                                                                         Computers—Storage and Memory Device
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