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How to Kill a Hard Drive

A new portable system completely cleans magnetic disks.
June 18, 2006

Researchers at the Georgia Tech Research Institute (GTRI) have developed a prototype that completely destroys a hard disk in a matter of seconds, clearing off all information and rendering the drive unusable. The disk erasure system, dubbed GuardDog, uses a 125-pound magnet that delivers a field comparable to the strength of a magnetic resonance imaging (MRI) machine. When exposed to the field, the magnetic media of a hard disk is scrubbed clean.

This prototype device is designed to erase the contents on magnetic hard disks quickly and completely, using a powerful magnetic field. The hard drive is passed through the device with a hand crank, because electrical methods would be disrupted by the magnetic field. (Courtesy of Michael Knotts, Georgia Tech Research Institute.)

The system, which currently fits inside a mini-fridge, contains an enclosed magnet with a slot large enough to accommodate a standard hard drive in its two-inch-thick steel-clad casing. The type of magnets used, called “permanent magnets,” can produce a consistently intense field, says Michael Knotts, a senior research scientist at GTRI and lead researcher on the project.

Using magnets to clear hard drives isn’t a new idea, says Jim Turner, senior staff research engineer at L-3 Communications ComCept, a defense contractor that collaborated on the project. However, the new system differs from other commercially available disk erasers in its speed, size, and effectiveness, he says. Consumer-grade systems rarely clean a disk entirely – and even alternative military-grade disk-killing approaches must physically destroy the disk by grinding it into a powder to ensure complete destruction. “Given sufficient time and resources [if the disk is not physically destroyed], it is theoretically possible to reconstruct the data,” Turner says.

Being able to erase drives completely and quickly could make GuardDog an effective system for the military, where a hard drive may need to be destroyed at a moment’s notice, explains Knotts. Although GuardDog was driven by specific military applications, though, its technology and design could also benefit banks, credit-card companies, and other organizations with sensitive personal information, Turner adds. Millions of hard drives are retired each year, many of them housing social-security and credit-card numbers. Ideally, all the data should be scoured from the drive before it’s tossed out.

GuardDog works by exploiting an extremely powerful magnetic material, called neodymium iron-boron, that produces a constant field without needing to be plugged into an electrical source or cooled to cryogenic temperatures. The strong magnetic field erases the disk by randomizing all of the magnetic dipoles in the material from their orientations when data was written to the disk. Because the field attracts steel components in the disk and its enclosure, a hand crank is used to overcome magnetic forces and pass the drive through the field. When the drive comes out, a few seconds later, the data has been removed. Knotts says that the magnet also ruins a hard-drive feature called “servo tracks” that are used to control the position of head that reads and writes data. In other words, the device not only removes the data, but also destroys the hard drive.

To test how well the system worked, the researchers used a technology called a magnetic force microscopy (MFM), which maps nanometer scale magnetic lines and spots on hard disks that are produced when data is stored. Depending on the orientation of these features, the researchers are able to determine how well their system worked: when a disk holds data, organized lines and spots are clearly visible with MFM; however, after a disk is destroyed, Knotts says, there are no longer such patterns.

The tool has some restrictions. “Imagine taking these systems around in an office,” Knotts says. “You don’t want stray magnetic fields messing up other hard drives, grabbing stray nuts and bolts, or disrupting pacemakers.” To keep the powerful magnetic field from operating outside GuardDog, the researchers developed a shielding based on the same magnets used to erase the disks. They simulated the field on a computer, Knotts explains, and found that small magnets placed outside the main magnet canceled out the field beyond the device.

Although being able to erase data completely is important, it’s unclear whether or not this method is necessary, says Simson Garfinkel, an expert on computer and data security (and an occasional contributor to Technology Review). He suggests that an encryption technique programmed into the hardware of a disk, called “crypto shredding,” can also completely erase a disk, and do so with the tap of a few keyboard buttons, instead of using a magnetic system. “Why bother with any of that?” he says.

Knotts counters that the government considers some applications to be so sensitive that even encryption is insufficient. And, he adds, for some applications it is crucial to be able to destroy drives during a power failure.

In fact, many ways exist for destroying a hard drive, from encryption to altering its magnetic properties, says Fred Spada, associate research scientist at the Center for Magnetic Recording Research at the University of California, San Diego. The research at GTRI has produced a useful new prototype that could erase information even when an encryption key is unavailable, he says; and it focuses on the standard that his research center is interested in: making sure “there’s no chance that there’s any magnetic signature that can be recovered by any means.”

Currently, L-3 Communications ComCept is looking to commercialize the technology within the next few years. Knotts says the GTRI team developed a miniature version of the device targeted at one-inch disk drives used in high-end cameras and that they are currently working to produce a smaller version of the prototype that would suit laptop hard drives.

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