Once the disk clusters that were occupied by a deleted file have been overwritten with new data, the file is gone forever. In fact, the old data may still be present on the magnetic media, as a kind of wiggle in the waveforms that represent the data. Using intricate, high-tech equipment, technicians first copy the exact waveform recorded on an area of the disk, without translating the signal into bits and bytes. They then generate a perfect waveform representing the corresponding data bits, subtract the perfect waveform from the actual waveform, and amplify the differences. Theoretically, you can even repeat the process, obtaining yet an earlier chunk of data.
Physical limitations preclude more than seven repetitions of the recovery process.
That doesn't mean you can recover seven layers of data, only that you can't recover more than seven. This level of recovery must be performed by experts, and is painstaking and expensive. In most cases, recreating the lost data from scratch is more cost-effective. Recovery Prevention Utilities. Even if you deleted the files or formatted the disk, a bored student with computer skills could have recovered your business files or personal data from the hard drive.