The Sudden Motion Sensor (SMS) is

Apple An apple is a round, edible fruit produced by an apple tree (''Malus'' spp.). Fruit trees of the orchard or domestic apple (''Malus domestica''), the most widely grown in the genus, are agriculture, cultivated worldwide. The tree originated ...

's motion-based

data protection Data protection may refer to: * Information privacy, also known as data privacy * Data security {{Authority control ...

system used in their 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-

SSD A solid-state drive (SSD) is a type of solid-state storage device that uses Integrated circuit, integrated circuits to store data persistence (computer science), persistently. It is sometimes called semiconductor storage device, solid-stat ...

portable systems (since October 2006), now the

MacBook Pro The MacBook Pro is a line of Mac laptop computers developed and manufactured by Apple. Introduced in 2006, it is the high-end sibling of the MacBook family, sitting above the ultra-portable MacBook Air and previously the low-end MacBook li ...

and

MacBook Air The MacBook Air is a line of Mac (computer), Mac laptop computers developed and manufactured by Apple Inc., Apple since 2008. It features a thin, light structure in a machining, machined aluminum case and currently either a 13-inch or 15-inch ...

. With a triaxial

accelerometer An accelerometer is a device that measures the proper acceleration of an object. Proper acceleration is the acceleration (the rate of change (mathematics), rate of change of velocity) of the object relative to an observer who is in free fall (tha ...

, the shock detector detects sudden

acceleration In mechanics, acceleration is the Rate (mathematics), rate of change of the velocity of an object with respect to time. Acceleration is one of several components of kinematics, the study of motion. Accelerations are Euclidean vector, vector ...

, such as when the computer is dropped, and prepares the relatively fragile

hard disk drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating hard disk drive platter, pla ...

mechanism for impact. The system disengages the disk drive heads from the hard disk platters, preventing data loss and drive damage from a 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 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

15",

uses the Kionix KXM52-1050 three-axis accelerometer chip, with dynamic range of +/- 2g and bandwidth up to 1.5 kHz.

Aftermarket hardware problems

Among the MacBook and MacBook Pro community there have been several owners who installed aftermarket hard drives already equipped with anti-shock features who reported experiencing kernel panic errors whenever their unit was physically moved. This is believed to be due to a conflict between SMS and the new drive's anti-shock function. The

Western Digital Western Digital Corporation is an American data storage company headquartered in San Jose, California. Established in 1970, the company is one of the world's largest manufacturers of hard disk drives (HDDs). History 1970s Western Digital ...

Scorpio series of notebook hard drives have been the most frequently reported as being susceptible to this problem. In practically all cases, disabling SMS alleviated this problem without any negative performance impact.{{according to whom, date=June 2019

External links

Apple.com: Sudden Motion Sensor disable instructionsAMSTracker by Amit Singh
Command line utility for reading data from the Sudden Motion Sensor Macintosh computers

Aftermarket hardware problems

See also

External links