There are three methods for "sanitizing" a hard drive: 1. Clearing: Overwriting the entire drive with new data so that the old data is no longer readable by a computer, although it may be possible to retrieve some data in a laboratory using signal processing equipment and specially trained personnel. 2. Purging: Removing the data at a more fundamental level, either using the drive's own controller electronics to carry out the task, or by degaussing (placing the drive in a machine that generates a strong magnetic field). Purging should remove all traces of data so that it is impossible to recover even if the storage medium is analysed in a laboratory. 3. Destroying: Physical destruction can be accomplished using a variety of methods, including disintegration, incineration, pulverizing, shredding, and melting. This article covers common tools and processes used for each method.