All algorithms for destruction of data are based on multiple overwrites of data on the hard disk drive sectors, or if from a physical stand point — on multiple switching of recording material over the disk surfaces.
Algorithms used in national governmental standards provide for filling each byte of each hard disk sector with ones, random values, or complimentary values to those written during the previous pass. Wiping implies at multiple passes on the hard disk.
For example, the U.S. national standard offers writing of the following:
- First pass — random values;
- Second pass — complimentary values to those written during the previous pass;
- Third pass — random values;
- Fourth pass — writing verification.