Head crash
Encyclopedia
A head crash is a hard-disk failure that occurs when a read–write head
of a hard disk
drive comes in contact with its rotating platter
, resulting in permanent and usually irreparable damage to the magnetic media on the platter surface.
A head normally rides on a thin film of moving air entrapped at the surface of its platter (some drives of the mid-1990s used a thin liquid layer instead). The topmost layer of the platter is made of a Teflon-like material that acts like a lubricant. Underneath is a layer of sputtered
carbon. These two layers protect the magnetic layer (data storage area) from most accidental touches of the read-write head.
The disk read-and-write head
is made using thin film techniques that include materials hard enough to scratch through the protective layers. A head crash can be initiated by a force that puts enough pressure on the platters from the heads to scratch through to the magnetic storage layer. A tiny particle of dirt or other detritus, excessive shock or vibration, or accidentally dropping a running drive can cause a head to bounce against its disk, destroying the thin magnetic coating on the area the heads come in contact with, and often damaging the heads in the process. After this initial crash, countless numbers of fine particles from the damaged area can land onto other areas and can cause more head crashes when the heads move over those particles, quickly causing significant damage and data loss
, and rendering the drive useless. Some modern hard disks incorporate free fall sensor
s to offer protection against head crashes caused by accidentally dropping the drive.
Since most modern drives spin at rates between 5,400 and 15,000 RPM
, the damage caused to the magnetic coating can be extensive. At 7,200 RPM the edge of the platter is traveling at over 120 kilometres per hour (74.6 mph), and as the crashed head drags over the platter surface the read-write head generally overheats, making the drive or at least parts of it unusable until the heads cool.
Older drives typically rotated far more slowly and had larger heads flying higher above the surface of the medium. However, since in many cases the medium was housed in a removable cartridge or pack and since air filtration was comparatively crude, crashes were fairly frequent and invariably expensive.
Disk read-and-write head
Disk read/write heads are the small parts of a disk drive, that move above the disk platter and transform platter's magnetic field into electrical current or vice versa – transform electrical current into magnetic field...
of a hard disk
Hard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
drive comes in contact with its rotating platter
Hard disk platter
A hard-disk platter is a component of a hard-disk drive: it is the circular disk on which the magnetic data is stored. The rigid nature of the platters in a hard drive is what gives them their name . Hard drives typically have several platters which are mounted on the same spindle...
, resulting in permanent and usually irreparable damage to the magnetic media on the platter surface.
A head normally rides on a thin film of moving air entrapped at the surface of its platter (some drives of the mid-1990s used a thin liquid layer instead). The topmost layer of the platter is made of a Teflon-like material that acts like a lubricant. Underneath is a layer of sputtered
Sputtering
Sputtering is a process whereby atoms are ejected from a solid target material due to bombardment of the target by energetic particles. It is commonly used for thin-film deposition, etching and analytical techniques .-Physics of sputtering:...
carbon. These two layers protect the magnetic layer (data storage area) from most accidental touches of the read-write head.
The disk read-and-write head
Disk read-and-write head
Disk read/write heads are the small parts of a disk drive, that move above the disk platter and transform platter's magnetic field into electrical current or vice versa – transform electrical current into magnetic field...
is made using thin film techniques that include materials hard enough to scratch through the protective layers. A head crash can be initiated by a force that puts enough pressure on the platters from the heads to scratch through to the magnetic storage layer. A tiny particle of dirt or other detritus, excessive shock or vibration, or accidentally dropping a running drive can cause a head to bounce against its disk, destroying the thin magnetic coating on the area the heads come in contact with, and often damaging the heads in the process. After this initial crash, countless numbers of fine particles from the damaged area can land onto other areas and can cause more head crashes when the heads move over those particles, quickly causing significant damage and data loss
Data loss
Data loss is an error condition in information systems in which information is destroyed by failures or neglect in storage, transmission, or processing. Information systems implement backup and disaster recovery equipment and processes to prevent data loss or restore lost data.Data loss is...
, and rendering the drive useless. Some modern hard disks incorporate free fall sensor
Free fall sensor
A free-fall sensor is a component of electronic devices that detects them being in a state of free fall .-Use:It is usually used to then apply safety measures, e.g. parking the head of a hard disk to prevent a head crash and resulting data loss upon impact...
s to offer protection against head crashes caused by accidentally dropping the drive.
Since most modern drives spin at rates between 5,400 and 15,000 RPM
Revolutions per minute
Revolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...
, the damage caused to the magnetic coating can be extensive. At 7,200 RPM the edge of the platter is traveling at over 120 kilometres per hour (74.6 mph), and as the crashed head drags over the platter surface the read-write head generally overheats, making the drive or at least parts of it unusable until the heads cool.