How do I format a Hard Drive to sell a computer

[jimthorn]

So I'm selling my old iBook and I want to format the hard drive so that the old data cannot be recovered. The simplest solution is to boot from the original OS X CD and Erase Disk. But I'm guessing that this process doesn't actually write over all the old data. So should I use a different app to write zeros or patterns to the disk first? I've read only a little about this, but I'm definitely a beginner on this topic. Has anyone done this, and if so, what's a good app? Is data easily recovered from an erased hard disk?

Any thoughts would be appreciated.

[Doctor Q]

When you format a disk with any disk utility, there should be an option to zero the data. It takes much longer, but that's what you want.