Disk failure
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In computing, a disk failure occurs when a hard disk drive malfunctions and the stored information cannot be accessed with a properly configured computer. A disk failure may occur in the course of normal operation, or due to an external factor such as exposure to fire or water or high magnetic waves, or suffering a sharp impact.
The severity of disk failures vary. The most notorious and famous kind is head crash, where the internal read-and-write head of the device touches a platter, or a magnetic data storage surface. A head crash usually incurs severe data loss, and data recovery attempts may cause further damage if not done by a specialist with proper equipment. A hard drive also includes controller electronics, which occasionally fail. In such cases, it may be possible to recover all data. Hard drive platters are coated with an extremely thin layer of non-electrostatic lubricant, so that the read-and-write head will simply glance off the surface of the platter should a collision occur. However, this head hovers mere micrometers from the platter's surface which makes a collision an acknowledged risk.
Many hard drive manufacturers include a Mean Time Between Failures figure on product packaging or in promotional literature. These are calculated by constantly running samples of the drive for a short amount of time, analyzing the resultant wear and tear upon the physical components of the drive, and extrapolating forward to provide a reasonable estimate of its lifespan. Since this fails to take into account phenomena such as the aforementioned head crash, external trauma (dropping or collision), power surges, and so forth, though, the Mean Time Between Failures number is not generally regarded as an accurate projection of a drive's lifespan.
The phenomenon of disk failure is not limited in scope to hard drives. Other media types are prone to failure; in the late 1990s the click of death, so called because affected drives would endlessly click when disks were inserted into them, plagued many users of Iomega's 100-megabyte Zip disks.
CD-ROM and DVD drives, with their ever-increasing read and write speeds, now rotate CD and DVD media at alarmingly fast speeds. Hairline cracks in such media--even invisible ones--are exacerbated by the immense centrifugal force exerted by the fast revolution, sometimes causing the disk to literally fragment within the drive.
Even 3½-inch floppy disks can fall victim to disk failure. If either the drive or the media is dirty, users may experience the buzz of death when attempting to access the drive.
