DBAN writes all 0s to the drive. Formatting does not. That's why DBAN takes as long as it does. All formatting does is it essentially just replaces the Master File Table with a blank one in the specified format. This makes the drive appear to be empty to an operating system. Now of course, this doesn't explain why formatting can take a long time. You see, the longer format (a.k.a. "full format") is simply the Quick Format plus a thorough scan for errors. So, the longer format is good to use on an old drive, or a drive that you might suspect need such a scan. A quick format is for a drive that's known to be good but you just want it to look like an empty drive again.
The only time it's good to use a program like DBAN is when you're selling your drive and the buyer will be someone you don't know and therefore can't trust. So if you're just going to be reusing the drive, then just format it with the Quick Format and then you'll be all set.
