Hard drive files are stored on areas of the disk called sectors, in units called clusters. Clusters can be strewn across the hard disk, or in a continuous line. A windows file system called NTFS or the older FAT system, logically orders data by assigning a file name to point to locations on the disk magnetic surface. The location contains all data pertaining to that file and the file name holds information about how to reorder or reassemble the data. Because the data may be located arbitrarily around the overall disk surface, it becomes very difficult for a data recovery expert to reconstruct the puzzle that is the complete file. So even if filenames could be recovered and the address on disk of the data could be found, there is no guarantee that all the necessary data can be restored to full original condition. So some, not all scenarios have successful outcomes.
According to a paper by Peter Gutman, New Zealand science professor, from 1996, it is proposed that data can be recovered from disk sectors that have been over written. He outlines how read/write disk heads never travel over the same exact area of the disk twice, so by using a scanning electron microscope, one can reveal a “ghost track” of the old sector. This was based on the type of hard disk drives that preceded the IDE or ATA style drives used commonly today.
Now with a massive increase in bit density per square inch, and a decrease in hard disk track widths (down to nano levels), the possibility of recovering data in this way has greatly reduced.
Thomas Feher has claimed that if a disk drive is opened in a hermetically safe, clean environment, specialized equipment can be used to read residual magnetic traces that surround the newly written tracks and extract old data, even if the data has been overwritten numerous additional times. He claims that one of the Companies that can achieve this level of high-tech data recovery is Kuert Information Management.