recovery your data

To understand we must remember what a hard drive looks like.

Briefly, it consists of a stack of rotating circular plates between which move readwrite heads controlled by an arm Usually in aluminum these trays are covered with a thin magnetic layer where data is stored and organized.

Each plate is divided into concentric tracks each byte containing 8 bits. Called cluster the smallest unit of disk space occupied by a file made up of at least one sector. It is the address of the clusters that gives the exact position of the data on the disk. 

They are listed by the file allocation table FAT, a kind of general index of the hard drive, which also defines their status: available, reserved busy or defective. When a cluster is declared available, the system is allowed to use the space it occupies. In write mode, the read-write head equipped with an electromagnet then sweeps the surface of the plate so as to generate in this sector a positive or negative local magnetic field that is translated, within each bit by 1 or 0. 

To get a better idea seen in the microspheres magnetic force, the surface of a hard drive is a bit like a landscape of mountains with magnetic peaks and valleys.