Final answer:
A head crash is a catastrophic event where a readwrite head makes contact with the hard disk's surface, potentially leading to data loss and damage. Modern hard drives use giant magnetoresistance, a nanotechnology that allows for increased data storage density.
Step-by-step explanation:
When a readwrite head makes contact with the hard disk's surface or with particles on its surface, a disaster called a head crash occurs. A head crash can result in severe data loss and damage to the hard disk itself. Hard drives use the principle of magnetic induction to read and write data, but modern drives typically use a technique known as giant magnetoresistance (GMR), which is one of the success stories of nanotechnology. GMR readout devices undergo a large change of electrical resistance when an applied magnetic field interacts with thin films of alternating ferromagnetic and nonmagnetic layers. This innovation has significantly increased the data density storage capabilities of hard drives.