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Different units of storage of data are:


                                         No. of bits/bytes                       Unit

                                               8 Bits                           1 Byte


                                            1024 Bytes                        1 Kilobyte

                                        1024 Kilobytes (KB)                  1 Megabyte


                                       1024 Megabytes (MB)                    1 Gigabyte

                                        1024 Gigabytes (GB)                   1 Terabyte


                                        1024 Terabytes (TB)                   1 Petabyte

                                        1024 Petabytes (PB)                   1 Exabyte


                                         1024 Exabytes (EB)                  1 Zettabyte


                                        1024 Zettabytes (ZB)                 1 Yottabyte

                                        1024 Yottabytes (YB)                 1 Brontobyte


                                       1024 Brontobytes (BB)                 1 Geopbyte


              Secondary Memory / Auxiliary Memory

              Secondary memory refers to the permanent storage of data. During the operation of a computer, the currently
              used data lies in the temporary memory. It may be lost if the computer is suddenly switched ‘OFF’. For this
              purpose, secondary memory is required, as it provides the necessary backup and storage of instructions or
              data that are permanent & can be retrieved back as and when required. It is also known as backup memory. It
              has a higher storage capacity than the primary storage/memory. There are various types of secondary storage
              devices. Some of them are:

              Magnetic Disks: Magnetic Disks are storage devices that are made up of several disks coated with magnetic
              material.

              The surface of each disk is marked with invisible circular tracks. The data is stored in the form of magnetic
              spots on a disk.

                Hard Disk: It is the most widely used internal storage magnetic disk. It is made a higher of spindles of smooth
              metallic plates coated with a thin layer of magnetic material. Each plate of a hard disk is called a platter. Each
              platter has two (read/write) heads, one on each side. Over the years, hard disks have been available in various
              storage capacities. E.g. 20 MB in earlier days to 160 GB, 320 GB, 500 GB, 1 TB, 5 TB, 6 TB, 12 TB, 16 TB and
              more in recent times.







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