The Sudden Motion Sensor (SMS) is
Apple
An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, where its wild ancestor, ' ...
's motion-based
data protection
Information privacy is the relationship between the collection and dissemination of data, technology, the public expectation of privacy, contextual information norms, and the legal and political issues surrounding them. It is also known as data pr ...
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
iBook is a line of laptop computers designed, manufactured, and sold by Apple Computer from 1999 to 2006. The line targeted entry-level, consumer and education markets, with lower specifications and prices than the PowerBook, Apple's higher-end ...
line July 26, 2005. Since that time, Apple has included the system in all of their non-
SSD portable systems (since October 2006), now the
MacBook Pro and
MacBook Air
The MacBook Air is a line of ultrabook computers developed and manufactured by Apple Inc. It consists of a full-size keyboard, a machined aluminum case, and, in the more modern versions, a thin light structure. The Air was originally position ...
.
With a triaxial
accelerometer
An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration (the rate of change of velocity) of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is acc ...
, the
shock detector detects sudden
acceleration
In mechanics, acceleration is the rate of change of the velocity of an object with respect to time. Accelerations are vector quantities (in that they have magnitude and direction). The orientation of an object's acceleration is given by t ...
, 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 platters coated with magne ...
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
MacBook Pro 15",
Apple
An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, where its wild ancestor, ' ...
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 (WDC, commonly known as Western Digital or WD) is an American computer drive manufacturer and data storage company, headquartered in San Jose, California. It designs, manufactures and sells data technology produc ...
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
See also
*
Active hard-drive protection In computer hardware, active hard-drive protection refers to technology that attempts to avoid or reduce mechanical damage to hard disk drives by preparing the disk prior to impact. This approach is mainly used in laptop computers that are frequentl ...
External links
Apple.com: Sudden Motion Sensor disable instructionsAMSTracker_by_Amit_Singh_Command_line_utility
_for_reading_data_from_the_Sudden_Motion_Sensor.html" ;"title="Command line utility">AMSTracker by Amit Singh Command line utility
for reading data from the Sudden Motion Sensor">Command line utility">AMSTracker by Amit Singh Command line utility
for reading data from the Sudden Motion Sensor
Macintosh computers