<s>
A	O
computer	B-Application
fan	I-Application
is	O
any	O
fan	O
inside	O
,	O
or	O
attached	O
to	O
,	O
a	O
computer	B-General_Concept
case	I-General_Concept
used	O
for	O
active	O
cooling	O
.	O
</s>
<s>
Computer	B-Application
fans	I-Application
commonly	O
come	O
in	O
standard	O
sizes	O
,	O
such	O
as	O
92mm	O
,	O
120mm	O
(	O
most	O
common	O
)	O
,	O
140mm	O
,	O
and	O
even	O
200220mm	O
.	O
</s>
<s>
Computer	B-Application
fans	I-Application
are	O
powered	O
and	O
controlled	O
using	O
3-pin	O
or	O
4-pin	O
fan	O
connectors	B-Protocol
.	O
</s>
<s>
While	O
in	O
earlier	O
personal	B-Device
computers	I-Device
it	O
was	O
possible	O
to	O
cool	O
most	O
components	O
using	O
natural	O
convection	O
(	O
passive	O
cooling	O
)	O
,	O
many	O
modern	O
components	O
require	O
more	O
effective	O
active	O
cooling	O
.	O
</s>
<s>
Fan	B-Device
control	I-Device
is	O
not	O
always	O
an	O
automatic	O
process	O
.	O
</s>
<s>
A	O
computer	O
's	O
BIOS	B-Operating_System
can	O
control	O
the	O
speed	O
of	O
the	O
built-in	O
fan	O
system	O
for	O
the	O
computer	O
.	O
</s>
<s>
A	O
user	O
can	O
even	O
supplement	O
this	O
function	O
with	O
additional	O
cooling	O
components	O
or	O
connect	O
a	O
manual	O
fan	B-Device
controller	I-Device
with	O
knobs	O
that	O
set	O
fans	O
to	O
different	O
speeds	O
.	O
</s>
<s>
Active	O
cooling	O
on	O
CPUs	B-Device
started	O
to	O
appear	O
on	O
the	O
Intel	B-General_Concept
80486	I-General_Concept
,	O
and	O
by	O
1997	O
was	O
standard	O
on	O
all	O
desktop	O
processors	O
.	O
</s>
<s>
Chassis	O
or	O
case	B-Application
fans	I-Application
,	O
usually	O
one	O
exhaust	O
fan	O
to	O
expel	O
heated	O
air	O
from	O
the	O
rear	O
and	O
optionally	O
an	O
intake	O
fan	O
to	O
draw	O
cooler	O
air	O
in	O
through	O
the	O
front	O
,	O
became	O
common	O
with	O
the	O
arrival	O
of	O
the	O
Pentium	B-General_Concept
4	I-General_Concept
in	O
late	O
2000	O
.	O
</s>
<s>
Fans	O
are	O
used	O
to	O
move	O
air	O
through	O
the	O
computer	B-General_Concept
case	I-General_Concept
.	O
</s>
<s>
Case	B-Application
fans	I-Application
may	O
be	O
placed	O
as	O
intake	O
fans	O
,	O
drawing	O
cooler	O
outside	O
air	O
in	O
through	O
the	O
front	O
or	O
bottom	O
of	O
the	O
chassis	O
(	O
where	O
it	O
may	O
also	O
be	O
drawn	O
over	O
the	O
internal	B-Device
hard	I-Device
drive	I-Device
racks	O
)	O
,	O
or	O
exhaust	O
fans	O
,	O
expelling	O
warm	O
air	O
through	O
the	O
top	O
or	O
rear	O
.	O
</s>
<s>
Some	O
ATX	B-Language
tower	B-General_Concept
cases	I-General_Concept
have	O
one	O
or	O
more	O
additional	O
vents	O
and	O
mounting	O
points	O
in	O
the	O
left	O
side	O
panel	O
where	O
one	O
or	O
more	O
fans	O
may	O
be	O
installed	O
to	O
blow	O
cool	O
air	O
directly	O
onto	O
the	O
motherboard	O
components	O
and	O
expansion	O
cards	O
,	O
which	O
are	O
among	O
the	O
largest	O
heat	O
sources	O
.	O
</s>
<s>
Standard	O
axial	O
case	B-Application
fans	I-Application
are	O
40	O
,	O
60	O
,	O
80	O
,	O
92	O
,	O
120	O
,	O
140	O
,	O
200	O
and	O
220mm	O
in	O
width	O
and	O
length	O
.	O
</s>
<s>
As	O
case	B-Application
fans	I-Application
are	O
often	O
the	O
most	O
readily	O
visible	O
form	O
of	O
cooling	O
on	O
a	O
PC	O
,	O
decorative	O
fans	O
are	O
widely	O
available	O
and	O
may	O
be	O
lit	O
with	O
LEDs	O
,	O
made	O
of	O
UV-reactive	O
plastic	O
,	O
and/or	O
covered	O
with	O
decorative	O
grilles	O
.	O
</s>
<s>
Decorative	O
fans	O
and	O
accessories	O
are	O
popular	O
with	O
case	B-Architecture
modders	I-Architecture
.	O
</s>
<s>
The	O
PSU	O
is	O
mainly	O
bottom-mounted	O
in	O
modern	O
PCs	B-Device
,	O
having	O
its	O
own	O
dedicated	O
intake	O
and	O
exhaust	O
vents	O
,	O
preferably	O
with	O
a	O
dust	O
filter	O
in	O
its	O
intake	O
vent	O
.	O
</s>
<s>
Used	O
to	O
cool	O
the	O
CPU	B-General_Concept
(	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
)	O
heatsink	O
.	O
</s>
<s>
Used	O
to	O
cool	O
the	O
heatsink	O
of	O
the	O
graphics	B-Architecture
processing	I-Architecture
unit	I-Architecture
or	O
the	O
memory	O
on	O
graphics	B-Device
cards	I-Device
.	O
</s>
<s>
These	O
fans	O
were	O
not	O
necessary	O
on	O
older	O
cards	O
because	O
of	O
their	O
low	O
power	O
dissipation	O
,	O
but	O
most	O
modern	O
graphics	B-Device
cards	I-Device
designed	O
for	O
3D	O
graphics	O
and	O
gaming	O
need	O
their	O
own	O
dedicated	O
cooling	O
fans	O
.	O
</s>
<s>
Some	O
of	O
the	O
higher	O
powered	O
cards	O
can	O
produce	O
more	O
heat	O
than	O
the	O
CPU	B-General_Concept
(	O
dissipating	O
up	O
to	O
350watts	O
)	O
,	O
so	O
effective	O
cooling	O
is	O
especially	O
important	O
.	O
</s>
<s>
Since	O
2010	O
,	O
graphics	B-Device
cards	I-Device
have	O
been	O
released	O
with	O
either	O
axial	O
fans	O
,	O
or	O
a	O
centrifugal	O
fan	O
also	O
known	O
as	O
a	O
blower	O
,	O
turbo	O
or	O
squirrel	O
cage	O
fan	O
.	O
</s>
<s>
Used	O
to	O
cool	O
the	O
heatsink	O
of	O
the	O
northbridge	O
of	O
a	O
motherboard	O
's	O
chipset	B-Device
;	O
this	O
may	O
be	O
needed	O
where	O
the	O
system	B-Architecture
bus	I-Architecture
is	O
significantly	O
overclocked	B-Application
and	O
dissipates	O
more	O
power	O
than	O
as	O
usual	O
,	O
but	O
may	O
otherwise	O
be	O
unnecessary	O
.	O
</s>
<s>
As	O
more	O
features	O
of	O
the	O
chipset	B-Device
are	O
integrated	O
into	O
the	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
,	O
the	O
role	O
of	O
the	O
chipset	B-Device
has	O
been	O
reduced	O
and	O
the	O
heat	O
generation	O
reduced	O
also	O
.	O
</s>
<s>
Fans	O
may	O
be	O
mounted	O
next	O
to	O
or	O
onto	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
for	O
cooling	O
purposes	O
.	O
</s>
<s>
Hard	B-Device
drives	I-Device
can	O
produce	O
considerable	O
heat	O
over	O
time	O
,	O
and	O
are	O
heat-sensitive	O
components	O
that	O
should	O
not	O
operate	O
at	O
excessive	O
temperatures	O
.	O
</s>
<s>
Faster-spinning	O
hard	B-Device
disks	I-Device
with	O
greater	O
heat	O
production	O
.	O
</s>
<s>
A	O
case	B-Application
fan	I-Application
may	O
be	O
mounted	O
on	O
a	O
radiator	O
attached	O
to	O
the	O
case	O
,	O
simultaneously	O
operating	O
to	O
cool	O
a	O
liquid	O
cooling	O
device	O
's	O
working	O
fluid	O
and	O
to	O
ventilate	O
the	O
case	O
.	O
</s>
<s>
In	O
laptops	B-Device
,	O
a	O
single	O
blower	O
fan	O
often	O
cools	O
a	O
heat	O
sink	O
connected	O
to	O
both	O
CPU	B-General_Concept
and	O
GPU	B-Architecture
using	O
heat	O
pipes	O
.	O
</s>
<s>
In	O
gaming	B-Device
laptops	I-Device
and	O
mobile	O
workstations	B-Device
,	O
two	O
or	O
more	O
heavy	O
duty	O
fans	O
may	O
be	O
used	O
.	O
</s>
<s>
In	O
rack-mounted	B-Application
servers	O
,	O
a	O
single	O
row	O
of	O
fans	O
may	O
operate	O
to	O
create	O
an	O
airflow	O
through	O
the	O
chassis	O
from	O
front	O
to	O
rear	O
,	O
which	O
is	O
directed	O
by	O
passive	O
ducts	O
or	O
shrouds	O
across	O
individual	O
components	O
 '	O
heat	O
sinks	O
.	O
</s>
<s>
Water-cooling	O
radiator	O
transfers	O
a	O
lot	O
of	O
heat	O
,	O
and	O
radiator	O
fans	O
have	O
large	O
static	O
pressure	O
(	O
opposed	O
to	O
case	B-Application
fans	I-Application
that	O
have	O
high	O
airflow	O
)	O
for	O
dissipating	O
heat	O
.	O
</s>
<s>
Laptop	B-Device
computers	I-Device
lack	O
large	O
openings	O
in	O
the	O
case	O
for	O
warm	O
air	O
to	O
escape	O
.	O
</s>
<s>
The	O
laptop	B-Device
may	O
be	O
placed	O
on	O
a	O
cooler	O
–	O
somewhat	O
like	O
a	O
tray	O
with	O
fans	O
built	O
in	O
–	O
to	O
ensure	O
adequate	O
cooling	O
.	O
</s>
<s>
Some	O
high-end	O
machines	O
(	O
including	O
many	O
servers	O
)	O
or	O
when	O
additional	O
reliability	O
is	O
required	O
,	O
other	O
chips	O
like	O
SATA/SAS	O
controller	O
,	O
high	O
speed	O
networking	O
controllers	O
(	O
40Gbps	O
Ethernet	O
,	O
Infiniband	B-Architecture
)	O
,	O
PCIe	O
switches	O
,	O
coprocessor	O
cards	O
(	O
for	O
example	O
some	O
Xeon	O
Phi	O
)	O
,	O
some	O
FPGA	B-Architecture
chips	O
,	O
south	O
bridges	O
are	O
also	O
actively	O
cooled	O
with	O
a	O
heatsink	O
and	O
a	O
dedicated	O
fan	O
.	O
</s>
<s>
Expansion	O
slot	O
fana	O
fan	O
mounted	O
in	O
one	O
of	O
the	O
PCI	B-Protocol
or	O
PCI	B-Protocol
Express	O
slots	O
,	O
usually	O
to	O
supply	O
additional	O
cooling	O
to	O
the	O
graphics	B-Device
cards	I-Device
,	O
or	O
to	O
expansion	O
cards	O
in	O
general	O
.	O
</s>
<s>
Memory	O
fan	O
modern	O
computer	B-General_Concept
memory	I-General_Concept
can	O
generate	O
enough	O
heat	O
that	O
active	O
cooling	O
may	O
be	O
necessary	O
,	O
usually	O
in	O
the	O
form	O
of	O
small	O
fans	O
positioned	O
above	O
the	O
memory	O
chips	O
.	O
</s>
<s>
This	O
applies	O
especially	O
when	O
the	O
memory	O
is	O
overclocked	B-Application
or	O
overvolted	O
,	O
or	O
when	O
the	O
memory	O
modules	O
include	O
active	O
logic	O
,	O
such	O
as	O
when	O
a	O
system	O
uses	O
Fully	B-General_Concept
Buffered	I-General_Concept
DIMMs	I-General_Concept
(	O
FB-DIMMs	B-General_Concept
)	O
.	O
</s>
<s>
Most	O
of	O
the	O
time	O
memory	O
modules	O
,	O
located	O
close	O
to	O
CPU	B-General_Concept
will	O
receive	O
enough	O
of	O
the	O
air	O
flow	O
from	O
the	O
case	O
or	O
CPU	B-Application
fan	I-Application
,	O
even	O
if	O
the	O
air	O
from	O
CPU	B-Application
fan	I-Application
and	O
radiator	O
is	O
warm	O
.	O
</s>
<s>
If	O
the	O
main	O
CPU	B-General_Concept
is	O
water	O
cooled	O
,	O
this	O
small	O
amount	O
of	O
airflow	O
might	O
be	O
missing	O
,	O
and	O
additional	O
care	O
about	O
some	O
airflow	O
in	O
a	O
case	O
or	O
a	O
dedicated	O
memory	O
cooling	O
is	O
required	O
.	O
</s>
<s>
High	O
power	O
voltage	O
regulators	O
(	O
VRM	O
)	O
often	O
using	O
switch	O
mode	O
power	O
supplies	O
do	O
generate	O
some	O
heat	O
due	O
to	O
power	O
losses	O
,	O
mostly	O
in	O
the	O
power	O
MOSFET	B-Architecture
and	O
in	O
an	O
inductor	O
(	O
choke	O
)	O
.	O
</s>
<s>
These	O
,	O
especially	O
in	O
overclocking	B-Application
situations	O
require	O
active	O
cooling	O
fan	O
together	O
with	O
heatsink	O
.	O
</s>
<s>
Most	O
of	O
the	O
MOSFETs	B-Architecture
will	O
operate	O
correctly	O
at	O
very	O
high	O
temperature	O
,	O
but	O
their	O
efficiency	O
will	O
be	O
lowered	O
and	O
potentially	O
lifespan	O
limited	O
.	O
</s>
<s>
Larger	O
fans	O
are	O
usually	O
used	O
for	O
cooling	O
case	O
,	O
CPUs	B-Device
with	O
large	O
heatsink	O
and	O
ATX	B-Language
power	O
supply	O
.	O
</s>
<s>
Smaller	O
fans	O
are	O
usually	O
used	O
for	O
cooling	O
CPUs	B-Device
with	O
small	O
heatsink	O
,	O
SFX	O
power	O
supply	O
,	O
graphics	B-Device
cards	I-Device
,	O
northbridges	O
,	O
etc	O
.	O
</s>
<s>
Fans	O
may	O
be	O
controlled	O
by	O
sensors	O
and	O
circuits	O
that	O
reduce	B-Device
their	I-Device
speed	I-Device
when	O
temperature	O
is	O
not	O
high	O
,	O
leading	O
to	O
quieter	O
operation	O
,	O
longer	O
life	O
,	O
and	O
lower	O
power	O
consumption	O
than	O
fixed-speed	O
fans	O
.	O
</s>
<s>
Most	O
computer	B-Application
fans	I-Application
use	O
one	O
of	O
the	O
following	O
bearing	O
types	O
:	O
</s>
<s>
Connectors	B-Protocol
usually	O
used	O
for	O
computer	B-Application
fans	I-Application
are	O
the	O
following	O
:	O
</s>
<s>
The	O
three	O
pins	O
are	O
used	O
for	O
ground	O
,	O
+12V	O
power	O
,	O
and	O
a	O
tachometer	B-Device
signal	O
.	O
</s>
<s>
The	O
additional	O
pin	O
is	O
used	O
for	O
a	O
pulse-width	B-Algorithm
modulation	I-Algorithm
(	O
PWM	O
)	O
signal	O
to	O
provide	O
variable	O
speed	O
control	O
.	O
</s>
<s>
This	O
is	O
the	O
same	O
connector	O
as	O
used	O
on	O
hard	B-Device
drives	I-Device
before	O
the	O
SATA	O
became	O
standard	O
.	O
</s>
<s>
This	O
connector	O
is	O
used	O
with	O
notebook	B-Device
fans	O
or	O
when	O
connecting	O
the	O
fan	O
to	O
the	O
video	B-Device
card	I-Device
.	O
</s>
<s>
Some	O
computer	B-Application
fans	I-Application
use	O
two-pin	O
connectors	B-Protocol
,	O
of	O
various	O
designs	O
.	O
</s>
