You must do a low level format.
A drive platter is made up of magnetic cells which shift, depending on what kind of charge the write head gives that particular cell.
Each cells can only be a 1 or 0.
A fully zeroed drive means it has been formatted at a low level.
During a low level format, every cell is set to 0.
During a quick format, only the boot record and the file structure tables are erased.
A manufacturers prep software may usually give you a low level format.
There are some apps out there that can do it also.
Formatting a drive from the dos prompt may or may not do it...im not sure...
Just google low level format or visit your manufacturer's site for utils.
A true low level format would delete completely everything on the drive, but the "low level" format utils out there will delete everything except servo, sector layout, and defect management.
A high level format will give you partitions, file systems....etc which can be done in dos using FDisk, partition magic, windows setup.....