The original paper ends with the conclusion that: In fact, this paper was misinterpreted and become the source of the 35-pass urban legend. Many tools have built-in settings to perform up to 35 write passes – this is known as the “Gutmann method,” after Peter Gutmann, who wrote an important paper on the subject - “ Secure Deletion of Data from Magnetic and Solid-State Memory,” published in 1996. This has led some people to theorize that, even after overwriting a sector, it may be possible to examine each sector’s magnetic field with a magnetic force microscope and determine its previous state.Īs a solution, many people advise writing data to the sectors multiple times. On a traditional mechanical hard disk drive, data is stored magnetically. SSDs have a limited number of write cycles, and wiping them will use up write cycles with no benefit. You also shouldn’t wipe SSDs – just deleting the files will do. This means that file-recovery tools won’t work on SSDs. On a solid state drive, it takes longer to overwrite a used sector rather than writing data to an unused sector, so erasing the sector ahead of time increases performance. When an operating system deletes a file from an SSD, it sends a TRIM command to the drive, and the drive erases the data. Newer solid state drives supporting the TRIM command behave differently. The above is only true for traditional, mechanical hard drives. When you “wipe” a drive, you overwrite all data on it with 0’s, 1’s, or a random mix of 0’s and 1’s. It doesn’t take any longer to overwrite a used sector, so there’s no point in wasting resources overwriting the data – unless you want to make it unrecoverable. A 10 GB file can be marked as unused very quickly, while it would take much longer to write over 10 GB of data on the drive.
Why doesn’t the operating system delete the data completely? That would take additional system resources. However, if you run a file-recovery utility, you can recover data from these sectors, assuming they haven’t been overwritten yet. The operating system marks the sectors containing the data as “unused.” The operating system will write over these unused sectors in the future. When you delete a file using Windows, Linux, or another operating system, the operating system doesn’t actually remove all traces of the file from your hard drive.
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