Degaussing

Degaussing removes data from magnetic storage by applying a magnetic field strong enough to disrupt the magnetic patterns that record it. It applies to hard disk drives and magnetic tape. NIST SP 800-88 Rev. 2 (2025) treats degaussing as a physical purge technique for magnetic media, a stronger method than clearing, but narrows its use. The degausser has to be matched to the media’s coercivity, meaning how strongly the media resists a change in magnetisation, and Rev. 2 notes that many existing degaussers lack the force for newer high-coercivity drives. It also states that degaussing does not count as destruction, even when it leaves a drive inoperable.

Degaussing commonly leaves a modern hard drive unusable, because it also erases the factory-written servo information the drive needs to position its heads, so it suits drives that will not be reused. An unusable drive is not proof of erasure, though: Rev. 2 warns that degaussing can damage the servo tracks yet fail to sanitise the data. It has no effect on solid-state drives, USB flash storage or optical discs, which do not store data magnetically; for those, cryptographic erase, built-in sanitise commands or physical destruction are the relevant options. Degaussing is one form of purging and is distinct from clearing by overwriting. The wider discipline is media sanitisation, which answers data remanence.

Exam relevance: a scenario is likely to offer degaussing as an option for an SSD or an optical disc, where it does not work. Candidates are expected to match the sanitisation method to the media type, and to note that degaussing usually ends a hard drive’s working life, while an unusable drive is not necessarily a sanitised one.