Head crash

A head crash in a modern drive

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A head crash is a hard disk failure that occurs when a read-write head of a hard disk drive touches its rotating platter in an area not intended for parking the head resulting in permanent and usually fatal damage to the magnetic media on the platter surface (see Hard disk platter).

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).^{[citation needed]} 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.

A head crash can be initiated by a tiny particle of dirt or other detritus which can cause a head to bounce against its disk, destroying the thin magnetic coating on the disk. 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 may also occur when a hard disk equipped device is accidentally dropped. Modern hard disks incorporate free fall sensors to offer protection against this.

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 74 miles per hour (120 km/h), 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. Following a head crash, particles of material scraped free of the drive surface greatly increase the chances of further head crashes or damage to the platters.

IBM RAMAC disk showing head crash damage

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.

Use of the term in printing

In large format printing, the term head crash refers to the sudden jamming of the print heads on the scan axis. Typically the result of print media bunching up, a head crash can result in damage to the print head, requiring replacement.

See also

• Active hard drive protection
• Click of death

External links

• Collection of sounds of failing hard drives.