There comes a time in the life of most computers when the user will face a need to erase a hard drive, and in some cases it is necessary to ensure that the drive is erased completely. This may occur when giving away a computer, when you want to make sure the new user won’t have access to your files. It may also occur when recycling an old computer or hard drive, to ensure no one is able to access sensitive documents. Or it may occur in a business environment, when one employee is leaving and a new employee is taking his place, to protect the privacy of both the employee and the company.
Whatever the reason, it is relatively easy to erase a hard drive completely, but it takes some special tools to make sure the data you’ve gotten rid of can’t be recovered. To understand why, it’s first important to understand how hard drives function, and most importantly how the delete key or recycling bin on your computer works. Many people think that by moving a file to the trash and erasing it, they’ve erased it completely, but in fact it takes quite a bit more than that to erase a hard drive or anything from it.
Hard drives consist of lots of data, which is marked in different ways. Files that are accessible are marked on the hard drive as space that is being used, and this means that when new files are created or existing files are changed, none of these files will be accidentally overwritten. When you move a file to the trash or recycling bin and empty it, you tell the computer to change the way that space on the hard drive is marked. The data is not actually removed, but in the future new data may overwrite it. If no data does overwrite it, however, it can be recovered quite easily using special software. Even if parts of the files are overwritten, often enough data can be recovered to reassemble large parts of documents.
To completely erase a hard drive, therefore, you need to not only mark the sections on the hard drive as ones that can be overwritten, you need to overwrite them completely. One way to do this, without special tools, is to use the built in disk utilities in Windows, Mac OSX, or Linux, to format the hard drive. Although not complete, a Full Format will largely overwrite everything, ensuring a fair level of erasure. This is often enough for people who just want to pass their computers on to charity, a friend, or to recycle them, and don’t have any truly sensitive documents on them.
For businesses or government employees, however, it may be important to ensure that when you erase a hard drive it stays erased even in the face of devoted attempts to recover the data. To do this, you’ll need a special piece of software, known as a data dump program or a disk wiping program. This program will overwrite the entire hard drive over and over again with completely random data, ensuring that almost nothing remains of the original. Different programs and standards differ in their degrees of completeness, ranging from medium to high-security forms. The most common standard, used by the US government, is the DoD 5220.22-M standard, which overwrites three times, first inscribing 1s on every bit of the drive, then 0s on every bit, and finally a government code of 246.