Format, Quick Format, Zero Drive
Many people don't actually know the differences between zeroing a hard drive, quick formatting a hard drive and formatting a hard drive. Many people think that one way is better than the other for all the wrong reasons. Each method has it's own suitable situation.
Throughout this little article I'm going to use an analogy of a village. In the village there are people, houses and a census bureau. With each type of format, you destroy a part of that village.
Quick Format
Quick formatting is simple. It removes the header information which describes the data on the drive. It doesn't actually touch the data itself, it just removes the information describing it. Because there is no record of the data existing, your drive appears to be empty. In reality all of the actual data is still there, you're just able to write over top of it because the file system doesn't know about it anymore. Quick formatting is not as inefficient as people make it out to be and is the option I would recommend for most situations when you know the drive is in good condition. You can recover most data from a quick format using software such as TestDisk
When you perform a quick format on your village, you're firing the employees at the census bureau and removing any paper trail left behind. Everyone still lives in the village, but nobody knows anything about who, what or where everyone is.
Format ("Slow" format)
With an ordinary format, or "Slow" format, you still only remove the header information but then the disk is scanned for bad sectors. This ensures that nothing is wrong on your disk when formatting and is the equivalent of running the chkdsk command in windows. I would recommend doing a regular format instead of a quick format if you haven't checked your disk in a long time and want to kill two birds with one stone. Like the quick format you can still recover files using software.
In our village, when you run a full format, you go into everyone's home and make sure they're all doing well. If anyone is sick or injured, you stamp a big red "BAD!" on their forehead and nobody ever talks to them or asks them to do anything. Then you fire the census employees and remove the paper trail of anyone ever existing.
"Zeroing" the drive
When you zero a hard drive you essentially remove all information "permanently" from the drive. All data is removed, not just the header information. A check for bad sectors is typically done as well. Zeroing your hard drive is usually done using disk management software such as SeaTools. I would recommend zeroing the hard drive if you have any sensitive data on it that you want to be removed or if you will be selling the drive to someone. Software is typically not a feasible option for recovery, but it is possible to recover the data through a data recovery service (see manufacturer website).
When you zero your village, you are essentially murdering all of the villagers and burying them. Then you're running a bulldozer through the houses and burying the debris. You've run through the census bureau with an automatic weapon and annihilated everyone and disposed of their bodies. The content of the village is essentially still there, but nobody can see it unless they dig down deep. Eventually the bodies decompose and it is nearly impossible to tell who the body belonged to or what they looked like.
Think about that little analogy the next time you need to format your hard drive. Do you really want to murder everyone in the village?
