hard disk drive (HDD, or also hard drive) is a fixed data storage device that stores data on a magnetic surface layered onto hard disk platters. A hard disk uses rigid rotating platters (disks). Each platter has a planar magnetic surface on which digital data may be stored. Information is written to the disk by transmitting an electromagnetic flux through an antenna or read-write head that is very close to a magnetic material, which in turn changes its polarization due to the flux. The information can be read by a read-write head which senses electrical change as the magnetic fields pass by in close proximity as the platter rotates.

Disk failure occurs when a hard disk drive no longer operates and the information on it can no longer be accessed by the computer. This can happen for no reason at all or due to an external factor such as exposure to fire or water or High Magneticwaves or suffering a sharp impact How seriously the disk failure is varies. The most serious and well-known kind is the head crash where the internal read-and-write head of the device touches a platter or a magnetic data storage surface. A head crash normally causes severe data loss and, moreover, data recovery attempts may cause further damage if not done by somebody with specialized knowledge.