Sudden Motion Sensor
Encyclopedia
The Sudden Motion Sensor (SMS) is Apple's patent-pending
motion-based hardware and data-protection 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 portable systems (since October 2006), now the MacBook
, MacBook Pro
, and MacBook Air
.
With a triaxial accelerometer
, the system 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 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 kicks in if you move your computer up and down for example.
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), whiles 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 uses the Kionix KXM52-1050 three-axis accelerometer chip, with dynamic range of +/- 2g and bandwidth up to 1.5 kHz.
The motion sensor can also be read by programs running on the Apple portables and a number of programs exist that use the motion sensor to make the computer tilt-aware http://osxbook.com/software/sms/. This way, tilting can be used as a human interface device
for instance for scrolling or for controlling games.
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
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.
Patent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....
motion-based hardware and data-protection system used in their notebook computer systems. Apple introduced the system January 1, 2005 in its refreshed PowerBook
PowerBook
The PowerBook was a line of Macintosh laptop computers that was designed, manufactured and sold by Apple Computer, Inc. from 1991 to 2006. During its lifetime, the PowerBook went through several major revisions and redesigns, often being the first to incorporate features that would later become...
line, and included it in the iBook
IBook
The iBook was a line of laptop computers sold by Apple Computer from 1999 to 2006. The line targeted the consumer and education markets, with lower specifications and prices than the PowerBook, Apple's higher-end line of laptop computers....
line July 26, 2005. Since that time, Apple has included the system in all of their portable systems (since October 2006), now the MacBook
MacBook
The MacBook was a brand of Macintosh notebook computers built by Apple Inc. First introduced in May 2006, it replaced the iBook and 12-inch PowerBook series of notebooks as a part of the Apple–Intel transition. Positioned as the low end of the MacBook family, the Apple MacBook was aimed at the...
, MacBook Pro
MacBook Pro
The MacBook Pro is a line of Macintosh portable computers introduced in January 2006 by Apple. It replaced the PowerBook G4 and was the second model, after the iMac, to be announced in the Apple–Intel transition...
, and MacBook Air
MacBook Air
The MacBook Air family is a line of Apple ultraportable Macintosh notebook computers.The first-generation MacBook Air was a 13.3"-only model, previously promoted as the World's Thinnest Notebook, introduced at the Macworld Conference & Expo on January 15, 2008. It featured a custom Intel Merom CPU...
.
With a triaxial accelerometer
Accelerometer
An accelerometer is a device that measures proper acceleration, also called the four-acceleration. This is not necessarily the same as the coordinate acceleration , but is rather the type of acceleration associated with the phenomenon of weight experienced by a test mass that resides in the frame...
, the system detects sudden acceleration
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...
, such as when the computer is dropped, and prepares the relatively fragile hard disk drive mechanism for impact. The system disengages the disk drive heads
Disk read-and-write head
Disk read/write heads are the small parts of a disk drive, that move above the disk platter and transform platter's magnetic field into electrical current or vice versa – transform electrical current into magnetic field...
from the hard disk platters, preventing data loss and drive damage from a disk head crash
Head crash
A head crash is a hard-disk failure that occurs when a read–write head of a hard disk drive comes in contact with its rotating platter, resulting in permanent and usually irreparable damage to the magnetic media on the platter surface....
. When the computer is stable, the drive operates normally again. A clicking noise can be heard when the sudden motion sensor kicks in if you move your computer up and down for example.
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
Gravitational acceleration
In physics, gravitational acceleration is the acceleration on an object caused by gravity. Neglecting friction such as air resistance, all small bodies accelerate in a gravitational field at the same rate relative to the center of mass....
(e.g. the dynamic range was close to 6-bit), whiles 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 uses the Kionix KXM52-1050 three-axis accelerometer chip, with dynamic range of +/- 2g and bandwidth up to 1.5 kHz.
The motion sensor can also be read by programs running on the Apple portables and a number of programs exist that use the motion sensor to make the computer tilt-aware http://osxbook.com/software/sms/. This way, tilting can be used as a human interface device
Human interface device
A human interface device or HID is a type of computer device that interacts directly with, and most often takes input from, humans and may deliver output to humans. The term "HID" most commonly refers to the USB-HID specification. The term was coined by Mike Van Flandern of Microsoft when he...
for instance for scrolling or for controlling games.
Aftermarket hardware issues
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 panicKernel panic
A kernel panic is an action taken by an operating system upon detecting an internal fatal error from which it cannot safely recover. The term is largely specific to Unix and Unix-like systems; for Microsoft Windows operating systems the equivalent term is "Bug check" .The kernel routines that...
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
Western Digital Corporation is one of the largest computer hard disk drive manufacturers in the world. It has a long history in the electronics industry as an integrated circuit maker and a storage products company. Western Digital was founded on April 23, 1970 by Alvin B...
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.
Similar systems
- IBMIBMInternational Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
, now Lenovo: Active Protection System, found in some ThinkPadThinkPadThinkPad is line of laptop computers originally sold by IBM but now produced by Lenovo. They are known for their boxy black design, which was modeled after a traditional Japanese lunchbox...
s starting in 2003. - AcerAcer (company)Acer Incorporated is a multinational information technology and electronics corporation headquartered in Xizhi, New Taipei City, Taiwan. Acer's products include desktop and laptop PCs, tablet computers, servers, storage devices, displays, smartphones and peripherals...
: GraviSense, found in some TravelMate-series notebooks manufactured in 2006. - HP: 3D DriveGuard and HP Mobile Data Protection System 3D.
- DellDellDell, Inc. is an American multinational information technology corporation based in 1 Dell Way, Round Rock, Texas, United States, that develops, sells and supports computers and related products and services. Bearing the name of its founder, Michael Dell, the company is one of the largest...
: ST Microelectronics DE351DL Motion Sensor is found on XPSXPSXPS may refer to:* X-ray photoelectron spectroscopy XPS, also known as ESCA* Exopolysaccharide, or extracellular polymeric substance, a sliming substance secreted by bacteria and responsible for cells adhesion onto surfaces and in biofilms...
L401X, L501X and L701X models.