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Primary Memory

        This is the main memory of the computer. CPU can directly access this memory. It is fixed on the
        motherboard of the computer. Primary memory is further divided  into  two types: Random Access
        Memory (RAM) and Read Only Memory (ROM).

        Random Access Memory (RAM)

        RAM is a temporary memory. The information stored in this memory is
        lost when the computer is turned OFF. That’s why it is also called volatile
        memory.                                                                                    RAM

                                Read Only Memory (ROM)

                                Information stored in ROM is permanent in nature, i.e., it holds the data even if
                                the system is switched OFF. It holds the instructions required to start a computer.
                                It is also called non-volatile memory.
            ROM
        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 as compared to primary memory. Secondary memory
        devices are also called secondary storage devices. They are divided in three categories: Magnetic Disks,
        Optical Discs and Flash Drives.

        Magnetic Disk

        A magnetic disk is covered with a magnetic coating. You can record and erase data on a magnetic disk
        any number of times.  The different types of magnetic disks are:

            Hard Disk: It consists of one or more magnetic disks called platters. It is
             permanently fixed in the CPU box. It comes in a variety of sizes with storage
             capacities as high as 5 TB (TeraByte) or even more.
            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.                               Hard disk


        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 fitted in the CPU box,
                                                      reads information stored on a compact disc (CD). CD is an
                                                      external storage device. It can hold up to 700 MB of data.
                                                      The different types of CDs are CD-ROM, CD-RW and CD-R.


                                                        Digital Versatile or Video Disc (DVD):  DVDs are now
                CD                    DVD
                                                      widely  used  to store data. A  DVD is  similar to a CD.  Its
                                                      storage capacity is 4.7 GB, much higher than a CD.




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