I want to write a program that can recover deleted files from hard drive ( FAT32/NTFS partition Windows). I don't know where to start from. What should be the starting point of this? What should i read to pursue this? Help is required. Which system level structs should i study?
It's entirely a matter of the filesystem layout, how a "file" actually looks on disk, and what remains when a file is deleted. As such, pretty much all you need to understand is the filesystem spec (for each and every filesystem you want to support), and how to get direct block-level access to the HD data. It might be possible to reuse some code from existing filesystem drivers, but it will need to be modified to process structures that, from the point of view of the filesystem, are gone.