Maleficent magnets and mangled megabytes

Personal computers have become common-place in physicians' practices and their use in cardiac pacing for programming and follow-up is increasing. The most commonly used media for mass data storage are ferromagnetic. That the toroidal and bar magnets used to activate reed switches pose a threat to such data is well known but the degree of care necessary in handling magnets around storage media, especially the vulnerable floppy diskettes, is not generally appreciated. The basic principles of magnetic data storage discussed herein elucidate the mechanism of data alteration by extraneous magnetic fields. The properties of the surface coatings, the requirements of applicable industry standards, and the field strengths of the pacemaker magnets suggest that data on diskettes should be secure if kept at least 6-7 cm from an isolated pacemaker magnet. Experiments with typical bar and toroidal magnets demonstrated that data recorded on representative diskettes actually remained unaltered until the magnets were placed < 1 cm from the recording surfaces.