Most computer users have experienced major failure leading to data loss at least once in their lives. The fault may lie with defective hardware, such as a seriously scratched hard disk, or corrupted software, whether due to a particularly strong virus or worm, or a pre-existing software bug. Fortunately, data recovery is possible in most cases.

Computer data consists of files and sectors. The operating system reads the files, while the hard disk reads the sectors. A file system bridges these two computer data components. Think of a file system as a two-column table, at its simplest: one column has the file name, while the other has the sector numbers.

When you create a file, the file system searches for empty rows in the table and fills the columns with the necessary information. If you search for a file, the system looks up the file name and matches it with the hard disk’s sector numbers. When you delete a file, it doesn’t completely disappear; the file system simply marks the part of the table where that file used to be as “available”.