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Read Only Memory (ROM)

                 Information stored in ROM is permanent in nature, that is, it holds the data

                 even if the system is switched off. It holds the starting instructions that
                 are required to start a computer. It is also called non-volatile memory.

                 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       Solid State     CD     DVD       Blu-ray Disc      Pen Drive     Memory Card
                                   Drive (SSD)

                 Magnetic Disk

                 A circular metallic disk covered with a magnetic coating, that is used for storing data, is called
                 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 hard disk 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 12 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 hard disks that will
                 be connected to any computer with the help of a USB port.





                          The first commercially available hard disk drive was the IBM 350 Disk File, which
                          was introduced by IBM in 1956. It had a storage capacity of about 3.75 MB.




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