Head crash
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A head crash occurs when the read-write head of a hard disk drive touches its rotating platter. The head normally rides on a thin film of moving air entrapped at the surface of the platter (some drives of the mid-1990s used a thin fluid layer instead). Higher capacity drives (using the same size and number of platters) are obtained by running the head closer to the platter. A tiny particle of dirt or other detritus can cause the head to bounce against the disk, destroying the thin magnetic coating on the disk. Since most modern drives spin at rates between 5,000 and 15,000 revolutions per minute, the damage caused by a head crash can be disastrous.