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Sudden Motion Sensor
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{{multiple| {{primarysources|date=July 2009}} {{Update|reason=the article is missing information about the SMS not being included in Macs with a solid-state drive |date=July 2017}} }} The '''Sudden Motion Sensor''' ('''SMS''') is [[Apple Inc.|Apple]]'s motion-based [[Information privacy|data protection]] system used in their [[notebook computer|notebook computer systems]]. Apple introduced the system January 1, 2005 in its refreshed [[PowerBook]] line, and included it in the [[iBook]] line July 26, 2005. Since that time, Apple has included the system in all of their non-[[Solid-state drive|SSD]] portable systems (since October 2006), now the [[MacBook Pro]] and [[MacBook Air]]. With a triaxial [[accelerometer]], the [[shock detector]] detects sudden [[acceleration]], such as when the computer is dropped, and prepares the relatively fragile [[hard disk drive]] mechanism for impact. The system disengages the [[disk read-and-write head|disk drive heads]] from the [[hard disk platters]], preventing data loss and drive damage from a [[head crash|disk head crash]]. When the computer is stable, the drive operates normally again. A clicking noise can be heard when the sudden motion sensor activates. Broadly speaking, there have been two types of Sudden Motion Sensor. The sensor used in the G4-based laptops resolved shifts of 1/52 [[gravitational acceleration|g]] (e.g. the dynamic range was close to 6-bit), while the sensor used in the current Intel-based laptops have an 8-bit resolution (250 scale divisions). In at least one model of Intel-based laptop, the [[MacBook Pro]] 15", [[Apple Inc.|Apple]] uses the Kionix KXM52-1050 three-axis accelerometer chip, with dynamic range of +/- 2g and bandwidth up to 1.5 kHz.
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