First of all, virtually every hard drive manufactured has bad sectors on it before it leaves the factory. A utility is run on the hard drive to find all the initial bad sectors and placed in a list. Every sector in the list is then remapped and saved to an area called the ‘Permanent Defect List’ or PList. It would be far too expensive to manufacturer a hard drive that every sector was perfect. The manufacturers take that into consideration so every drive that is made has a pool of sectors that is used only if a bad sector is found.
True. But by the time you start seeing bad sectors t's time to replace the drive.