like what was said above, a quick format removes the file index. Think of it like a book. The story would be the data, and the table of contents referencing the chapter and its name would be the index. However, with a computer, if you delete the the index, it has NO idea how to access the info. With just a normal delete (through windows) the data is ALSO there, just the pointer/index to it is removed, essentialy marking the file as available for use. The data is there, its just not indexed. Writing zeros does just what it says. It writes zeros across the entire drive, which should not be done on older drives as some had they're settings on a special partition, but newer drives this is contained via chipset on the drive. Even writing zeros, though, the info can still be gotten by computer forensics (because writing a '0' over a '1' still contains a slight charge, and sensitive machines can pick that up... writing a '0' over a '0' will not). So the only way for data to be unreadable is by a disk killing program which alternatley writes 1111 0000 1111 all across the HDD and then does other patterns. So any data gotten would be a jumbled mess, after writing zeros.
If you argue with an idiot he will drag you down to his level and beat you with experience.
I am not a fast writer.
I am not a slow writer.
I am a half-fast writer.