Bad sectors are sections of your computer’s hard drive that have been damaged, and have lost the ability to save and store your data. http://www.dolphindatalab.com/product/new-wd-firmware-repair-hardware-dfl-wdii/
This video shows how to repair bad sectors , how to depop heads, format with plist, self-scan, how to repair bad HDD.
In most cases, bad sectors are the result of internal physical damage in your computer, such as magnetic disk failure, and can sometimes corrupt your saved data. Bad sectors are usually indicated by grinding or chugging noises inside of your computer or from error messages that inform you that data cannot be saved to your disk drive.