<s>
The	O
Sudden	B-Device
Motion	I-Device
Sensor	I-Device
(	O
SMS	O
)	O
is	O
Apple	O
's	O
motion-based	O
data	O
protection	O
system	O
used	O
in	O
their	O
notebook	B-Device
computer	I-Device
systems	I-Device
.	O
</s>
<s>
Apple	O
introduced	O
the	O
system	O
January	O
1	O
,	O
2005	O
in	O
its	O
refreshed	O
PowerBook	B-Device
line	O
,	O
and	O
included	O
it	O
in	O
the	O
iBook	B-Device
line	O
July	O
26	O
,	O
2005	O
.	O
</s>
<s>
Since	O
that	O
time	O
,	O
Apple	O
has	O
included	O
the	O
system	O
in	O
all	O
of	O
their	O
non-SSD	O
portable	O
systems	O
(	O
since	O
October	O
2006	O
)	O
,	O
now	O
the	O
MacBook	B-Device
Pro	I-Device
and	O
MacBook	B-Device
Air	I-Device
.	O
</s>
<s>
With	O
a	O
triaxial	O
accelerometer	O
,	O
the	O
shock	O
detector	O
detects	O
sudden	O
acceleration	O
,	O
such	O
as	O
when	O
the	O
computer	O
is	O
dropped	O
,	O
and	O
prepares	O
the	O
relatively	O
fragile	O
hard	B-Device
disk	I-Device
drive	I-Device
mechanism	O
for	O
impact	O
.	O
</s>
<s>
The	O
system	O
disengages	O
the	O
disk	B-Device
drive	I-Device
heads	I-Device
from	O
the	O
hard	B-Device
disk	I-Device
platters	I-Device
,	O
preventing	O
data	O
loss	O
and	O
drive	O
damage	O
from	O
a	O
disk	B-Device
head	I-Device
crash	O
.	O
</s>
<s>
A	O
clicking	O
noise	O
can	O
be	O
heard	O
when	O
the	O
sudden	B-Device
motion	I-Device
sensor	I-Device
activates	O
.	O
</s>
<s>
Broadly	O
speaking	O
,	O
there	O
have	O
been	O
two	O
types	O
of	O
Sudden	B-Device
Motion	I-Device
Sensor	I-Device
.	O
</s>
<s>
The	O
sensor	O
used	O
in	O
the	O
G4-based	O
laptops	B-Device
resolved	O
shifts	O
of	O
1/52	O
g	O
(	O
e.g.	O
</s>
<s>
the	O
dynamic	O
range	O
was	O
close	O
to	O
6-bit	O
)	O
,	O
while	O
the	O
sensor	O
used	O
in	O
the	O
current	O
Intel-based	O
laptops	B-Device
have	O
an	O
8-bit	O
resolution	O
(	O
250	O
scale	O
divisions	O
)	O
.	O
</s>
<s>
In	O
at	O
least	O
one	O
model	O
of	O
Intel-based	O
laptop	B-Device
,	O
the	O
MacBook	B-Device
Pro	I-Device
15	O
"	O
,	O
Apple	O
uses	O
the	O
Kionix	O
KXM52-1050	O
three-axis	O
accelerometer	O
chip	O
,	O
with	O
dynamic	O
range	O
of	O
+	O
/	O
-	O
2g	O
and	O
bandwidth	O
up	O
to	O
1.5kHz	O
.	O
</s>
<s>
Among	O
the	O
MacBook	O
and	O
MacBook	B-Device
Pro	I-Device
community	O
there	O
have	O
been	O
several	O
owners	O
who	O
installed	O
aftermarket	O
hard	B-Device
drives	I-Device
already	O
equipped	O
with	O
anti-shock	O
features	O
who	O
reported	O
experiencing	O
kernel	B-Operating_System
panic	I-Operating_System
errors	O
whenever	O
their	O
unit	O
was	O
physically	O
moved	O
.	O
</s>
<s>
The	O
Western	O
Digital	O
Scorpio	O
series	O
of	O
notebook	B-Device
hard	B-Device
drives	I-Device
have	O
been	O
the	O
most	O
frequently	O
reported	O
as	O
being	O
susceptible	O
to	O
this	O
problem	O
.	O
</s>
