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Magnetic Disk

                 A hard disk coated with a magnetic layer is called a magnetic disk. You can record
                 and erase data on a magnetic disk multiple 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 where data is recorded using a magnetic head. It is

                 permanently fixed inside the computer system. It is usually
                 used for  permanent data  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 (Terabytes) 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

                  Clickipedia




                   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.







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