Why Do Magnets Mess Up Computers?

By G.S. Jackson

Household magnets do not contain enough strength to damage hard drive data.
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A hard drive is the "library" of a computer; it holds most of the computer's data, including data for the operating system and for long-term storage. The hard drive is typically not in danger of damage, since it resides inside the computer. One way to possibly damage a hard drive is through demagnetization. In order to understand how this is possible, you must understand how hard drives store data, how hard drives interact with magnets and how magnets work when reacting with each other.

Hard Drive Basics

Hard drives function through the use of magnetism. Inside a hard drive, a series of platters coated with a magnetically pliable substance containing magnetic particles spin along a central axis. Multiple read/write "heads" detect the positions of the particles in the magnetic substance on the platters to read the data. The positioning of each particle corresponds to either a zero or a one, as storage takes place in binary numbers. Other types of storage, such as flash memory drives or solid state drives do not function this way and are not affected by magnets.

Theory of Magnetic Destruction

The theory behind magnetic destruction of hard drives is that as a magnet comes close to the platters of a hard drive, damage occurs. The idea is that the magnet disrupts the state of the magnetic particles on the platters, thus "scrambling" the data and rendering it irretrievable. Once a series of particles has changed states -- switched from zero to one or vice-versa -- and the operating system or hard drive operating software are not informed, then the data is essentially deleted; no program with scrambled data can run effectively, and no information can be reliably read.

Coercivity and Magnetism

One thing to consider when thinking about magnets and hard drives is the "coercivity" of the magnet. The coercivity of any magnetic field is the amount of magnetic force of the opposite polarity is required to demagnetize that field. The substance on the platters, being a magnetic substance, has a particular coercivity that, should a powerful enough magnetic field exert force on the platter, the platters could lose magnetic force and the data be erased.

Reality of Magnetic Destruction

Hard drive research has focused on maintaining drives in the face of outside forces such as magnets. The coercive factor of modern hard drives far exceeds the force of household magnets: the demagnetization of a modern hard drive requires a super-powered magnet called a "degaussing" machine. In fact, hard drives contain magnets mere centimeters from the spinning plates that run the read/write arms. These magnets do not affect the plates because the plates are so resistant to demagnetization. The risk of damaging a hard drive from magnetization as part of normal usage is very slight.