A head crash is triggered by a faulty function of the read/write head of a hard disk or floppy disk drive. This can be due to strong mechanical impairments such as the effects of shocks or impacts, but also to protracted wear.
In general, hard disks and removable disks operate without contact, with the read/write head hovering a short distance above the disk surface. In perfect operation, the read/write heads float on a cushion of air above the magnetic layer at a distance of about 50 nm, with the disks rotating at up to 10,000 rpm.
However, if a read/write head hits the magnetic layer of a hard disk, a head crash occurs and the data carrier is damaged. The data stored at this point is destroyed, and the entire hard disk may be damaged.