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Software overwriting writes gibberish onto the hard
drive three times.
FIGURE 7-6 Overwriting a hard drive with random data enables preexisting data to be completely removed.

This is an appealing solution because there are plenty of applications you can buy to do
this; plus it can be done in-house. Additionally, overwritten drives can be used again. They
can be used within your organization or you can sell them.
On the other hand, software overwriting is a time-consuming process. It can take several
hours to wipe one drive. This can cause a loss of productivity, especially in an organization
that is overwriting hundreds or even thousands of hard drives.

NOTE Sometimes cost can also be an issue. Some software requires a separate licensing fee for each
hard drive that’s being overwritten.

Degaussing
If you remember VHS videocassettes, you may also remember the warning labels on them
to keep them away from magnets. There was a good reason for this—a powerful enough
magnetic force could erase a videocassette. This is also known as degaussing.
Degaussing uses a machine that produces a strong electromagnetic field and destroys
the information stored on a hard drive. Degaussing was done in the past with weaker
magnets; however, the magnetically shielded hard drives of today call for a stronger
electromagnetic field.
Although the zap from the electromagnet is quick, it also destroys other components of
the hard drive, leaving them inoperable. As such, they cannot be reused and you don’t
know for sure if all the data has been erased.
You also have to take care when using a degaussing machine. While wiping one hard
drive, you run the risk of destroying other machines that might be in the area.