Fly Height Detection

The height at which the heads fly above the hard disk platters is one of the most important design parameters of any hard disk. The reason is that this gap represents a critical design trade-off: if the heads are too high above the surface of the disk the heads then data errors can occur, but if they are too low, the risk of a head crash dramatically increases. The fly height of the heads must be maintained within tight parameters to ensure the reliability of the drive.

Many manufacturers are now incorporating sensors into their drives to monitor the height at which the heads float over the surface of the platters. This is usually used as one of the data inputs to the drive's SMART feature, as any trend downward in fly height can signal the possibility of a head crash in the near future.

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