Degaussing is the process of reducing a magnetic field. It can be used to reset the magnetic field of a CRT monitor or to destroy the data on a magnetic storage device.
A CRT monitor displays images by firing electrons through a cathode ray tube (CRT) onto the screen. The electron beams are focused by a plate near the screen called a shadow mask. If this plate becomes unevenly magnetized by surrounding objects or simply the earth's magnetic field, it can cause discoloration on the screen. Therefore, CRT monitors often include a "Degauss" command that resets the magnetic field when run. Since it is impossible to eliminate the magnetic charge inside the monitor, the degaussing process realigns or randomizes the magnetic field, which provides consistent colors across the screen.
Degaussing may also be used to destroy the data on a magnetic storage device, such as a hard drive or tape drive. A hard drive degausser, for example, includes a chamber where you can insert a hard drive. When you run the degausser, it uses a process called capacitative discharge to decrease the drive's magnetic field, making any data on the drive unreadable. The cycle time, which is the time it takes for the data to be erased, varies between degaussers, but is usually between ten seconds and one minute. Companies and government organizations may use degaussers to eliminate the data on storage devices before reprovisioning or discarding them.