How to know witten data266)?

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now i require to know which memory location the data is stored

Why do you need to know that ? If you need to know what is in the file you can read it back and if you need to modify it you can read it, modify it and save it again.

One of the advantages of using a file system is you don't need to know the data's physical address. All you need to know is the name of the file.