Head-Crash

The head crash is the direct contact with the surface of a magnetic disk ( platter ) of a hard drive by the read-write head, which results in mechanical damage to the storage layer. There is a risk of destruction and loss of data. In extreme cases, the write head crash, in a stick on the platter surface and are then torn off by the rotation of the platter.

After a head crash the hard drive is usually no longer bootable, or only runs for a short time until it fails permanently. This is caused in most cases by abraded material which is deposited as a thin film on the platter and then the heads and the surface of the platter also lead to damage. Further damage the data -bearing surface can thus occur in a renewed attempt to start that the heads are positioned by the electronics in other, previously unaffected areas. The data on a hard drive can be saved only by data recovery companies with specialized equipment after a head crash often.

Causes

There is normally due to ground effect between the read-write head and the rapidly rotating platters surface a thin cushion of air ( " Plain bearing " - the same effect as when aquaplaning ). To keep the heads in position, you need a constant high speed of the disk. Is now reduced, for example by a fault in the engine control, the rotation speed to low values ​​, the magnetic sensors of the read and write heads can be placed on the surface of the storage medium.

Other common reasons for head- crash, wear, improper installation of the hard drive, wide temperature fluctuations, general vibrations (which are more common among mobile devices, such as Microdrives in digital cameras and notebooks ) and blackouts or dirt on the platter surfaces.

Countermeasures

• The car park function is parked (since 1989 ) the failure of the power supply automatically the heads in the landing zone ( by utilizing the rotational energy of the plates).
• As protection from falls some ThinkPad models have mentioned since about 2003, APS ( Active Protection System ) motion sensor that shuts down the drive head in the park position when accelerations are registered, which could lead to a head crash.
• In Apple laptops a Sudden Motion Sensor is installed since January 2005, the case of strong motion by the write of your hard drive, preventing data loss. Also some Microdrives are already equipped with a system which observes shocks and retrieve instantly write heads in the landing zone.
• In order to prevent placement of the heads resulting from a low rotational speed in modern hard drives airlock system is used, which parks the head at too low a speed.