I am selling my HDD and I want to erase it. I would like to use DBAN, but it doesn't erase HPA and DCO, my question is, does it matter? What data can be here? And my second question - if I wipe HPA with DCO, can I normally install Windows afterwards, doesn't it damage the disc? Thanks.
Many different types of hardware write-blockers (e.g., wiebetech brand) will identify the HPA and DCO and remove them for you if you choose. Once the HPA and DCO are gone then wiping the disk, e.g., with dd, will remove all the data. E.g., supposing the disk to be wiped is at /dev/hdc:
sudo dd if=/dev/zero of=/dev/hdc
will get rid of everything if there is no DCO/HPA.
The information stored in the HPA/DCO is usually put there by the manufacturer and so the HPA/DCO should not contain any of your personal data. I.e., you're probably fine just not worrying about the HPA/DCO and wiping with DBAN.
If you wipe the HPA/DCO you should still be able to install Windows afterwards, it should not damage the disk... I'm pretty sure of this... although I wouldn't bet my life on it...