<s>
Fan	B-Device
control	I-Device
is	O
the	O
management	O
of	O
the	O
rotational	O
speed	O
of	O
an	O
electric	O
fan	O
.	O
</s>
<s>
In	O
computers	O
,	O
various	O
types	O
of	O
computer	B-Application
fans	I-Application
are	O
used	O
to	O
provide	O
adequate	O
cooling	B-General_Concept
,	O
and	O
different	O
fan	B-Device
control	I-Device
mechanisms	O
balance	O
their	O
cooling	B-General_Concept
capacities	O
and	O
noise	O
they	O
generate	O
.	O
</s>
<s>
This	O
is	O
commonly	O
accomplished	O
by	O
the	O
motherboards	B-Device
having	O
hardware	B-Application
monitoring	I-Application
circuitry	O
,	O
which	O
can	O
be	O
configured	O
by	O
the	O
end-user	O
through	O
BIOS	B-Operating_System
or	O
other	O
software	O
to	O
perform	O
fan	B-Device
control	I-Device
.	O
</s>
<s>
As	O
modern	O
PCs	B-Device
grow	O
more	O
powerful	O
so	O
do	O
their	O
requirements	O
for	O
electrical	O
power	O
.	O
</s>
<s>
Computers	O
emit	O
this	O
electrical	O
power	O
as	O
heat	O
generated	O
by	O
all	O
major	B-Architecture
components	I-Architecture
.	O
</s>
<s>
Heat	O
production	O
varies	O
with	O
system	O
load	O
,	O
where	O
periods	O
of	O
compute-intensive	O
activity	O
generate	O
much	O
more	O
heat	O
than	O
the	O
idle	B-Algorithm
time	O
does	O
.	O
</s>
<s>
Processors	O
in	O
most	O
early	O
x86-based	O
computers	O
,	O
up	O
to	O
some	O
of	O
the	O
early	O
486s	B-General_Concept
,	O
did	O
not	O
need	O
active	O
ventilation	O
.	O
</s>
<s>
Power	O
supplies	O
needed	O
forced	O
cooling	B-General_Concept
,	O
and	O
power	O
supply	O
fans	O
also	O
circulated	O
cooling	B-General_Concept
air	O
through	O
the	O
rest	O
of	O
the	O
PC	O
with	O
the	O
ATX	B-Language
standard	O
.	O
</s>
<s>
Fans	O
installed	O
in	O
a	O
PC	B-General_Concept
case	I-General_Concept
can	O
produce	O
noise	O
levels	O
of	O
up	O
to	O
70dB	O
.	O
</s>
<s>
The	O
common	O
cooling	B-General_Concept
fans	O
used	O
in	O
computers	O
use	O
standardized	O
connectors	O
with	O
two	O
to	O
four	O
pins	O
.	O
</s>
<s>
Control	O
input	O
a	O
pulse-width	B-Algorithm
modulation	I-Algorithm
(	O
PWM	B-Algorithm
)	O
input	O
signal	O
,	O
used	O
when	O
the	O
cooling	B-General_Concept
fan	O
assembly	O
has	O
an	O
internal	O
motor	O
driver	O
circuit	O
.	O
</s>
<s>
Fan	O
assemblies	O
with	O
this	O
control	O
input	O
provide	O
the	O
ability	O
to	O
adjust	O
the	O
rotational	O
speed	O
of	O
the	O
fan	O
without	O
changing	O
the	O
input	O
voltage	O
delivered	O
to	O
the	O
cooling	B-General_Concept
fan	O
assembly	O
.	O
</s>
<s>
A	O
variable	O
rotation	O
speed	O
allows	O
the	O
cooling	B-General_Concept
rate	O
to	O
be	O
adjusted	O
to	O
meet	O
demand	O
,	O
quietening	O
the	O
fan	O
and	O
saving	O
energy	O
when	O
full	O
speed	O
is	O
not	O
required	O
.	O
</s>
<s>
Cooling	B-General_Concept
fans	O
equipped	O
with	O
either	O
two	O
-	O
or	O
three-pin	O
connectors	O
are	O
usually	O
designed	O
to	O
accept	O
a	O
wide	O
range	O
of	O
input	O
voltages	O
,	O
which	O
directly	O
affects	O
the	O
rotation	O
speed	O
of	O
the	O
blades	O
.	O
</s>
<s>
In	O
this	O
style	O
of	O
fan	B-Device
control	I-Device
,	O
the	O
fan	O
is	O
either	O
on	O
or	O
off	O
.	O
</s>
<s>
A	O
standard	O
cooling	B-General_Concept
fan	O
is	O
a	O
DC	O
motor	O
with	O
blades	O
attached	O
.	O
</s>
<s>
Resistors	O
in	O
series	O
with	O
a	O
fan	O
's	O
power	O
pin	O
are	O
the	O
simplest	O
method	O
of	O
reducing	O
fan	O
noise	O
,	O
but	O
they	O
add	O
to	O
the	O
heat	O
generated	O
inside	O
the	O
computer	B-General_Concept
case	I-General_Concept
.	O
</s>
<s>
For	O
variable	O
fan	B-Device
control	I-Device
,	O
potentiometers	B-Device
could	O
be	O
used	O
along	O
with	O
a	O
transistor	B-Application
such	O
as	O
a	O
MOSFET	B-Architecture
whose	O
output	O
voltage	O
is	O
controlled	O
by	O
the	O
potentiometer	B-Device
.	O
</s>
<s>
The	O
power	O
rating	O
should	O
be	O
noted	O
and	O
some	O
diodes	O
may	O
require	O
cooling	B-General_Concept
to	O
operate	O
at	O
their	O
rated	O
current	O
.	O
</s>
<s>
The	O
voltage	O
a	O
computer	B-Application
cooling	I-Application
fan	I-Application
receives	O
is	O
defined	O
by	O
the	O
difference	O
between	O
the	O
voltage	O
wire	O
( +12V	O
)	O
and	O
the	O
ground	O
wire	O
( +0V	O
)	O
.	O
</s>
<s>
Through	O
this	O
procedure	O
,	O
10	O
,	O
17	O
and	O
24V	O
voltages	O
can	O
be	O
achieved	O
,	O
with	O
voltages	O
exceeding	O
12V	O
being	O
potentially	O
damaging	O
to	O
the	O
computer	B-Application
fans	I-Application
rated	O
at	O
12V	O
.	O
</s>
<s>
when	O
PC	O
enters	O
idle/sleep	O
state	O
)	O
.	O
</s>
<s>
Adjustable	O
versions	O
like	O
the	O
popular	O
LM317	O
also	O
exist	O
;	O
when	O
combined	O
with	O
a	O
potentiometer	B-Device
,	O
these	O
adjustable	O
regulators	O
allow	O
the	O
user	O
to	O
vary	O
the	O
fan	O
speed	O
of	O
several	O
fans	O
at	O
currents	O
far	O
in	O
excess	O
of	O
what	O
a	O
standard	O
potentiometer	B-Device
could	O
handle	O
.	O
</s>
<s>
For	O
higher	O
currents	O
,	O
discrete	O
linear	O
regulators	O
are	O
relatively	O
simple	O
to	O
construct	O
using	O
a	O
power	O
transistor	B-Application
or	O
MOSFET	B-Architecture
and	O
a	O
small	O
signal	O
transistor	B-Application
or	O
a	O
Zener	O
diode	O
as	O
a	O
voltage	O
reference	O
.	O
</s>
<s>
While	O
discrete	O
regulators	O
require	O
additional	O
components	O
(	O
a	O
minimum	O
of	O
two	O
transistors	B-Application
,	O
three	O
resistors	O
and	O
a	O
small	O
capacitor	O
)	O
,	O
they	O
allow	O
for	O
arbitrarily	O
high	O
currents	O
,	O
allowing	O
for	O
the	O
regulation	O
of	O
additional	O
fans	O
and	O
accessories	O
.	O
</s>
<s>
Pulse-width	B-Algorithm
modulation	I-Algorithm
(	O
PWM	B-Algorithm
)	O
is	O
a	O
common	O
method	O
of	O
controlling	O
computer	B-Application
fans	I-Application
.	O
</s>
<s>
A	O
PWM-capable	O
fan	O
is	O
usually	O
connected	O
to	O
a	O
4-pin	O
connector	O
(	O
pinout	O
:	O
Ground	O
,	O
+12V	O
,	O
sense	O
,	O
control	O
)	O
.	O
</s>
<s>
Many	O
motherboards	B-Device
feature	O
firmware	O
and	O
software	O
that	O
regulates	O
these	O
fans	O
based	O
on	O
processor	O
and	O
computer	B-General_Concept
case	I-General_Concept
temperatures	O
.	O
</s>
<s>
Another	O
method	O
,	O
popular	O
with	O
PC	B-Architecture
hardware	I-Architecture
enthusiasts	O
,	O
is	O
the	O
manual	O
fan	O
speed	O
controller	O
.	O
</s>
<s>
They	O
can	O
be	O
mounted	O
in	O
an	O
expansion	O
slot	O
or	O
a	O
5.25	O
"	O
or	O
3.5	O
"	O
drive	B-Device
bay	I-Device
or	O
come	O
built	O
into	O
a	O
computer	O
's	O
case	O
.	O
</s>
<s>
Most	O
modern	O
motherboards	B-Device
feature	O
hardware	B-Application
monitoring	I-Application
chips	O
,	O
which	O
are	O
capable	O
of	O
performing	O
fan	B-Device
control	I-Device
,	O
usually	O
through	O
the	O
PWM	B-Algorithm
method	O
as	O
described	O
above	O
.	O
</s>
<s>
These	O
chips	O
can	O
be	O
configured	O
through	O
BIOS	B-Operating_System
,	O
or	O
by	O
using	O
specialised	O
software	O
once	O
the	O
operating	O
system	O
has	O
booted	O
.	O
</s>
<s>
Processors	O
produce	O
varying	O
levels	O
of	O
heat	O
depending	O
on	O
system	O
load	O
,	O
thus	O
it	O
makes	O
sense	O
to	O
reduce	O
the	O
speed	O
of	O
the	O
fans	O
during	O
idle	B-Algorithm
to	O
decrease	O
the	O
noise	O
produced	O
by	O
fans	O
running	O
full	O
speed	O
,	O
until	O
the	O
load	O
does	O
goes	O
up	O
,	O
at	O
which	O
point	O
fan	O
speed	O
must	O
be	O
adjusted	O
promptly	O
to	O
avoid	O
overheating	O
.	O
</s>
<s>
Modern	O
hardware	B-Architecture
monitor	O
chips	O
,	O
once	O
configured	O
,	O
are	O
capable	O
of	O
independently	O
running	O
this	O
monitoring	O
loop	O
without	O
any	O
need	O
for	O
a	O
functioning	O
BIOS	B-Operating_System
or	O
an	O
operating	O
system	O
.	O
</s>
<s>
However	O
,	O
not	O
all	O
software	O
is	O
capable	O
of	O
accessing	O
these	O
advanced	O
configuration	O
parameters	O
provided	O
by	O
some	O
chips	O
,	O
and	O
it	O
is	O
very	O
common	O
that	O
the	O
generic	O
software	O
implements	O
only	O
the	O
most	O
basic	O
interfacing	B-Application
with	O
the	O
chips	O
,	O
namely	O
,	O
an	O
explicit	O
setting	O
for	O
the	O
duty	O
cycle	O
for	O
each	O
fan	B-Device
control	I-Device
setting	O
,	O
subsequently	O
performing	O
the	O
duty	O
cycle	O
adjustments	O
itself	O
in	O
software	O
,	O
and	O
thus	O
requiring	O
that	O
both	O
the	O
operating	O
system	O
,	O
as	O
well	O
as	O
this	O
third-party	O
software	O
itself	O
to	O
continue	O
running	O
on	O
the	O
main	O
CPU	O
to	O
perform	O
the	O
monitoring	O
loop	O
.	O
</s>
<s>
This	O
may	O
not	O
be	O
a	O
problem	O
until	O
the	O
system	O
or	O
the	O
utility	O
crashes	O
,	O
at	O
which	O
point	O
the	O
system	O
may	O
overheat	O
due	O
to	O
the	O
failure	O
of	O
the	O
fans	O
to	O
maintain	O
adequate	O
cooling	B-General_Concept
whilst	O
running	O
at	O
reduced	O
voltage	O
and	O
speed	O
.	O
</s>
<s>
Many	O
companies	O
now	O
provide	O
software	O
to	O
control	O
fan	O
speeds	O
on	O
their	O
motherboards	B-Device
under	O
Microsoft	B-Application
Windows	I-Application
or	O
Mac	O
OS	O
X/MacOS	O
.	O
</s>
<s>
Different	O
software	O
is	O
used	O
by	O
different	O
motherboards	B-Device
.	O
</s>
<s>
There	O
are	O
also	O
third-party	O
programs	O
that	O
work	O
on	O
a	O
variety	O
of	O
motherboards	B-Device
and	O
allow	O
wide	O
customization	O
of	O
fan	O
behavior	O
depending	O
on	O
temperature	O
readings	O
from	O
the	O
motherboard	B-Device
,	O
CPU	O
,	O
and	O
GPU	O
sensors	O
,	O
as	O
well	O
as	O
allowing	O
manual	O
control	O
.	O
</s>
<s>
Two	O
such	O
programs	O
are	O
SpeedFan	B-Language
and	O
Argus	O
Monitor	O
.	O
</s>
