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Hard Disk
                 The  hard  disk consists of  one  or  more  magnetic disks
                 called platters. Each disk in the pack has top and bottom

                 surfaces on which data is recorded using a magnetic head.
                 It is permanently fixed in the computer system. It is usually
                 used for  permanent mass storage.  The  most important
                 function of the hard disk  is  to store  program  files and
                                                                                                    Hard disk
                 data files.
                 The hard  disk comes in a variety  of sizes  with different

                 storage capacities as high as 5 TB (TeraByte) or even more.
                 The CPU accesses data stored on a hard disk much faster
                 than it can access data on a CD.

                 External  hard disks are  also available. They can be
                 connected to any computer with the help of a USB port.
                                                                                               External hard disk
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                   The first hard disk was introduced by Seagate in 1980, which could hold 5 MB of data.



                 Optical Disc

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

                 Compact Disc (CD)
                 The CD drive reads information stored on a compact disc
                 (CD). CD is an external storage device. The lifespan of an

                 optical disc is longer than a magnetic disk. It can hold up to
                 700 MB of data.
                 CD drive is usually connected inside the CPU box but can                            CD-Drive
                 also be connected using a USB port.

                 Types of CDs:
                 1.  CD-ROM (Compact Disc Read-Only Memory): A CD-ROM is

                    a pre-recorded CD containing data or software that has been
                    written at the time of manufacturing. The data stored 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
                                                                                                           CD
                    or erased later.


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