What are bad sectors?Normally, bad sectors are always present in the hard disk. It is almost impossible to eliminate them completely due to cost reasons. However, it is usually contained in the service area of the drive (generally referred to as the P-list) and will not be visited by the read write head. As a result, the user will not even notice the existence of bad sectors.
As time goes by, due to wear and tear, more bad sectors may develop. Some modern disks have the capabilities of including the newly developed bad sectors on the fly. This will involve moving those bad sectors to the growing G-list and some times data reallocation is needed. However, user will hardly notice such background process.
Bad sectors are actually degeneration of the magnetic surface of the hard disk platters. So it is considered as some kind of physical damage.
In the more severe cases, as bad sectors have the tendency to induce more bad sectors, the disk may eventually break down completely. In the worst scenario, it may also induce a head crash.
When this happens, you may experience system getting slower and slower until it completely crashes.
When you encounter bad sectors, backup your data immediately, especially valuable data.