Overwriting
Writing new data, such as a fixed pattern of zeros, over the locations that held old data on storage media, so the original contents can no longer be read back by ordinary means.
Overwriting replaces stored data by writing a pattern, commonly zeros, ones or random values, over the locations that held it. When software on the host writes over every user-addressable location, NIST SP 800-88 Rev. 2 treats it as a clearing technique. The guideline observes that overwriting typically hinders recovery even with laboratory techniques, and states that multi-pass schemes, such as the patterns once taken from DoD 5220.22-M, are not needed. An overwrite run by the drive itself, through a dedicated sanitize command that also reaches areas the host cannot address, can qualify as purging.
Overwriting depends on the media. On solid-state drives, wear levelling and spare capacity mean a host-based overwrite may never touch some cells that still hold old data, so cryptographic erase or a firmware sanitize command is the usual alternative. Write-once optical media cannot be overwritten at all, and a failed drive may not accept writes; in those cases physical destruction is the fallback.
Exam relevance: a scenario may propose overwriting for a solid-state drive or a CD-R and ask whether it is adequate. Candidates are expected to accept overwriting for magnetic drives that stay under organisational control, and to reject it where the media cannot be reliably or physically overwritten.