I used to work with a system that had replaceable disk packs -- think 18" diameter removable hard drives transported in a plastic dome. They had read heads tha

I used to work with a system that had replaceable disk packs -- think 18" diameter removable hard drives transported in a plastic dome. They had read heads that were driven by a linear motor, which was an absolutely huge electromagnet. Extended use would sometimes "walk" the equipment out of position (much like an out-of-balance washing machine), so it was common to put rubber doorstops under it to prevent this. One of the drive tests performed during maintenance was a random seek. Normally, the head position was controlled by a servo with a feedback loop, but this one time the servo failed and the magnet drove the head assembly out the back of the equipment and into the wall .. right at crotch height. There was a supplemental maintenance instruction issued shortly afterward to limit the use of that procedure, and to not stand behind the equipment when it was being run.