Importantly, of course, you don't need to run these commands from Linux for a Linux system. You can boot a Linux Live CD (like the popular Ubuntu Live CDs) and run the commands on Windows drives in a machine. Again, unless you have very specific requirements, there's little need to pay for wiping software.
Magnetic Degaussing
Of course, software isn't the only option to wipe a drive. Mechanical drives rely on magnetic properties to store bits, so if you don't trust software wiping, you could wipe it with a magnet instead.
A very powerful magnet, that is. Known as degaussing, strong magnets are moved around the drive creating moving magnetic fields that scramble and effectively destroy the data stored on the media. Degaussing has an advantage in that the entire surface of the disk is affected, wiping out partition tables, boot sectors and low-level formatting information in addition to stored data. This usually renders (especially with low-level format data destroyed) the drive inoperable and recoverable only by sending it back to the manufacturer--assuming the magnetic pulse doesn't destroy the motor in the process, too. Considering commercial degaussing can cost anywhere between $30k and $140k, this is probably the type of result you're looking for.
That does leave the rest of us in a bit of a pinch, can you degauss a drive yourself with a strong magnet? Yes, mostly. Rare earth Neodymium magnets are readily available online and exhibit extremely strong fields--enough to lift a thousand times their own weight. Using them on a drive is said to be very effective, but like commercial degaussers, may leave the drive inoperable (which if you're planning to sell the cleaned drives, may not be what you want). We can't recommend this route as Neodymium magnets can be physically dangerous if not handled correctly.
How We Tested
A cleanly formatted disk was set aside for each test on the testing machine, to which example files were then copied across. For programs that could both individually wipe files, and programs that wipe whole disks, we first noted the sectors where the files reside by booting a Linux Live-CD from USB and using the hdparm command with the '-- fibmap' and '--readsector' switches. This allowed us to find and raw-read the sectors on the drive where a file resides.
The files or disk was then wiped from within Windows, after which the machine was again booted to Linux and the same sectors where the files resided were read to confirm they no longer contain the data (or more correctly, contained scrambled or zeroed data).
Wipe times weren't measured, as all products saturate and are limited by the speed of the I/O subsystem.
Adding SSDs to the Mix
