Sometimes we need some data or variable values to be retained back even after the system is turned off. So as soon as we again start back the system  we need to know the previous values of some elements to identify the state of the system at shut down. So that now we can resume directly from that state only, not the initial state.  In many cases this is required.



  • In GSM based devices,  To save the custom mobile number of user which is being changed sometimes.
  •  For sensor interfacing examples, if we want to create a log of frequent values then we can also use to store values one by one with some by time delay . And so can get whole data logged.

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