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How to Erase a Hard Drive Safely and Completely

March 23, 2009

in applications,computer hardware,data storage and recovery,privacy & security,Windows

by David Hakala

If you plan to sell, give away, or just toss in the trash an old hard drive, you really should erase your personal data from it first. If you’re like most people, your hard drive contains things you don’t want strangers to see: private correspondence, bank account numbers, passwords, your children’s pictures, names, and where they go to school… think about it, then take a little time to wipe that hard drive really clean!

Deleting files, formatting a hard drive or even deleting its partition(s) does not erase the data on the drive completely. It just makes the data invisible to ordinary operating systems and programs. Specialized software can still read the data. Criminals as well as law enforcement agents have such software. Hard drive recovery specialists have retrieved vital data from drives that had holes drilled clear through them.

The best way to completely and irretrievably “erase” data from a hard drive is to bury it deeply under other, nonsensical data. The magnetic platters in a hard drive are divided into tiny regions that are magnetized or demagnetized to represent 1 and 0 bits, respectively. Change a 1 to a 0 once and the 0 is “erased”, but the 0 state remains detectable by the right software. The more times you change a given region’s magnetic state, the fainter its original state becomes and the more difficult it is to detect the original state. Your bank account number is worth only so much money, time, and effort to anyone.

Several free “data destruction” programs write random 0s and 1s onto every region of a hard drive as many times as you wish, making it impractical to recover your data even if it’s theoretically possible. But it can take a lot of time – dozens of hours for a 350 MB hard drive – to overwrite every tiny region just once. You have to make a trade-off between effort and security when erasing a hard drive.

DBAN (Darik’s Boot And Nuke) is a free and highly effective data destruction program that you can use to virtually guarantee that no one will be able to read your old drive. It comes as a boot disk, so you can start your computer from a DBAN disk and erase your C: drive if you wish. DBAN comes in several configurations to be installed on CD or DVD discs; floppy disks or USB drives; Apple Power Macs; or recent Intel and AMD processor-based computers.

David Hakala has perpetrated technology tutorials since 1988 in addition to committing tech journalism, documentation, Web sites, marketing collateral, and profitable prose in general. His complete rap sheet can be seen at

{ 1 comment }

Stewart Vardaman 03.24.09 at 2:04 am

dban is a much faster than that on newer PCs. Several years ago I was wiping 60-120 gig drives within two hours.

If you are merely throwing away your drive, the process is much quicker – smash it a few times with a hammer until you see dust from the platters seeping out. Even the NSA can’t decode that type of “encryption” 🙂

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