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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                   The human brain can hold about 2.5

                     is  not  directly  accessed  by  the  CPU.  It           petabytes of information, equivalent
                     allows  users  to  store  data  that  may  be               to a TV show being played for
                                                                               approximately 342 years non stop.
                     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.

                                                                                       Data Storage and Memory     9

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