I want to completely wipe all the data and both OSes (Ubuntu and Windows 7) from my hard drive. I tried DBAN but it gives me an error and does not run. I am looking for an alternative. After reading some articles online, I came to know that, using a Linux live CD, it can be done using either of following commands.
sudo dd if=/dev/zero of=/dev/sda
sudo shred -vfz -n 1 /dev/sda
My questions are
1) Which option (a or b) is more secure (wipes everything) and faster?
2) Does either of the options damage the hard drive or anything? I want the hard drive to be usable again for Windows and Ubuntu etc.
I have one more interesting and related question.
3) Options a) and b) write zeros to every bit. Do they do that if the bit is already zero or do they leave it since it is zero.