Physical sector damageA sector is the smallest unit of allocation for disk type media. A sector, for most all disk type media, holds 512 bytes of data although the sector and all of its components is actually larger than that. There are many sectors on a hard drive, for example, a 40 gigabyte hard drive will have approximately 80 million sectors available to store data. A single unreadable sector can corrupt an entire database.
Sector damage can be caused by several different things. The most common of which is head bounce where the heads have actually touched the surface of the media. Another is media degradation wherein the magnetic media itself is fading and losing its periodicity. Due to file system fragmentation, all possible sectors must be read from the drive and sometimes can take a while; we need your patience here.