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Secondary Memory

                 This memory is permanent in nature and is not directly accessed by the CPU. It allows users

                 to store data that may be easily retrieved. It is cheaper compared to primary memory.
                 Secondary memory devices are also called secondary storage devices. They are categorised

                 into three types:
                                                  Secondary Storage Devices




                         Magnetic Disk                    Optical Disc                    Flash Drive




                           Hard Disk            CD    DVD       Blu-Ray Disc      Pen Drive      Memory Card



                 Magnetic Disk

                 A circular metallic disk covered with a magnetic coating, that is used for storing data, is
                 callled a Magnetic disk. You can record and erase data on a magnetic disk any number of
                 times.

                 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 data files.

                 The hard disk comes in a variety of sizes with 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 are the hard disks that
                 can be connected to any computer with the help of a USB port.





                          The  first  hard  disk  was  introduced  by  Seagate  in  1979,  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. The lifespan of an optical disc is longer than a magnetic disk.


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