You’ll notice that the title of this article does not say format a hard drive but rather erase.
Most people are under the assumption that formatting a hard drive erases everything on it. Not true. A formatted drive can have its data recovered easily with utilities like this one.
Residual data that remains on a hard drive after it’s been formatted is referred to as data remanence.
While it is said that there is no way to truly erase a hard drive, low level formatting using what’s commonly known as a "DoD-7" will make it extremely difficult to recover data once this type of formatting has been performed.
The technical name for the DoD-7 is the US Department of Defense’s standard "National Industry Security Program Operating Manual" (US DoD 5220.22-M ECE). This formatting method overwrites a file seven times and is considered secure.
The DoD’s approach is, "Overwrite all addressable locations with a character, its complement, then a random character and verify."
DoD-7 formats take a very long to complete, usually several hours. For some larger drives it may take the better half of a day before it’s finished.
When it is appropriate to perform DoD-7 formats?
For normal home use it’s not necessary since you are the one using the hard drive. However if you’re selling a hard drive or selling a computer with a hard drive you’ve used before, you should DoD-7 format it. Doing so gives you peace of mind that whoever gets your drive or computer won’t get access to any data that was on there before.
How can you perform a DoD-7 format?
There are both free and paid utilities to do this task.
One of the better paid utilities is KillDisk. This software is very convenient because not only will it install to a floppy disk, but also make a self-bootable USB stick or CD. Most of you out there would probably use a USB stick. Simply pop the stick in, run the software, choose the appropriate drive letter and you’ll have a boot-ready stick in a few short minutes. It has both DOS and Windows options, but to be honest the DOS version is easier and loads much faster.
A freeware utility that many swear by is Darik’s Boot and Nuke, commonly known as DBAN. It’s not as easy to use or configure as KillDisk is, but it definitely does the job.
Final note: Concerning low level formatting of this type, there is literally no reason to have a Windows style environment to do it. It is completely unnecessary to have VGA resolution and a mouse pointer just to perform a format. Do it the DOS/terminal way because it’s the best, fastest and most efficient.