<s>
Computer	B-General_Concept
cooling	I-General_Concept
is	O
required	O
to	O
remove	O
the	O
waste	O
heat	O
produced	O
by	O
computer	B-Architecture
components	I-Architecture
,	O
to	O
keep	O
components	O
within	O
permissible	O
operating	O
temperature	O
limits	O
.	O
</s>
<s>
Components	O
that	O
are	O
susceptible	O
to	O
temporary	O
malfunction	O
or	O
permanent	O
failure	O
if	O
overheated	O
include	O
integrated	O
circuits	O
such	O
as	O
central	B-General_Concept
processing	I-General_Concept
units	I-General_Concept
(	O
CPUs	O
)	O
,	O
chipsets	B-Device
,	O
graphics	B-Device
cards	I-Device
,	O
and	O
hard	B-Device
disk	I-Device
drives	I-Device
.	O
</s>
<s>
Computer	B-Application
fans	I-Application
are	O
widely	O
used	O
along	O
with	O
heatsink	O
fans	O
to	O
reduce	O
temperature	O
by	O
actively	O
exhausting	O
hot	O
air	O
.	O
</s>
<s>
Components	O
commonly	O
individually	O
cooled	O
include	O
the	O
CPU	B-General_Concept
,	O
graphics	B-Architecture
processing	I-Architecture
unit	I-Architecture
(	O
GPU	B-Architecture
)	O
and	O
the	O
northbridge	B-Device
.	O
</s>
<s>
CPU	B-General_Concept
and	O
GPU	B-Architecture
)	O
are	O
the	O
main	O
generators	O
of	O
heat	O
in	O
modern	O
computers	O
.	O
</s>
<s>
Dust	O
acting	O
as	O
a	O
thermal	O
insulator	O
and	O
impeding	O
airflow	O
,	O
thereby	O
reducing	O
heatsink	O
and	O
fan	B-Application
performance	O
.	O
</s>
<s>
A	O
computer	O
with	O
thermal	O
sensors	O
integrated	O
in	O
the	O
CPU	B-General_Concept
,	O
motherboard	B-Device
,	O
chipset	B-Device
,	O
or	O
GPU	B-Architecture
can	O
shut	O
itself	O
down	O
when	O
high	O
temperatures	O
are	O
detected	O
to	O
prevent	O
permanent	O
damage	O
,	O
although	O
this	O
may	O
not	O
completely	O
guarantee	O
long-term	O
safe	O
operation	O
.	O
</s>
<s>
Before	O
an	O
overheating	O
component	O
reaches	O
this	O
point	O
,	O
it	O
may	O
be	O
"	O
throttled	O
"	O
until	O
temperatures	O
fall	O
below	O
a	O
safe	O
point	O
using	O
dynamic	B-General_Concept
frequency	I-General_Concept
scaling	I-General_Concept
technology	O
.	O
</s>
<s>
For	O
desktop	O
and	O
notebook	O
computers	O
,	O
throttling	O
is	O
often	O
controlled	O
at	O
the	O
BIOS	B-Operating_System
level	O
.	O
</s>
<s>
Throttling	O
is	O
also	O
commonly	O
used	O
to	O
manage	O
temperatures	O
in	O
smartphones	B-Application
and	O
tablets	O
,	O
where	O
components	O
are	O
packed	O
tightly	O
together	O
with	O
little	O
to	O
no	O
active	O
cooling	O
,	O
and	O
with	O
additional	O
heat	O
transferred	O
from	O
the	O
hand	O
of	O
the	O
user	O
.	O
</s>
<s>
They	O
can	O
perform	O
a	O
visual	O
inspection	O
of	O
the	O
cooler	O
and	O
case	B-Application
fans	I-Application
.	O
</s>
<s>
The	O
user	O
should	O
also	O
clean	O
the	O
fans	O
thoroughly	O
,	O
since	O
dust	O
and	O
debris	O
can	O
increase	O
the	O
ambient	O
case	O
temperature	O
and	O
impact	O
fan	B-Application
performance	O
.	O
</s>
<s>
Starting	O
in	O
1965	O
,	O
IBM	O
and	O
other	O
manufacturers	O
of	O
mainframe	B-Architecture
computers	I-Architecture
sponsored	O
intensive	O
research	O
into	O
the	O
physics	O
of	O
cooling	O
densely	O
packed	O
integrated	O
circuits	O
.	O
</s>
<s>
IBM	O
developed	O
three	O
generations	O
of	O
the	O
Thermal	B-General_Concept
Conduction	I-General_Concept
Module	I-General_Concept
(	O
TCM	O
)	O
which	O
used	O
a	O
water-cooled	O
cold	O
plate	O
in	O
direct	O
thermal	O
contact	O
with	O
integrated	O
circuit	O
packages	O
.	O
</s>
<s>
Systems	O
using	O
TCMs	O
were	O
the	O
3081	B-Device
family	O
(	O
1980	O
)	O
,	O
ES/3090	B-Device
(	O
1984	O
)	O
and	O
some	O
models	O
of	O
the	O
ES/9000	B-Device
(	O
1990	O
)	O
.	O
</s>
<s>
In	O
the	O
IBM	B-Device
3081	I-Device
processor	O
,	O
TCMs	O
allowed	O
up	O
to	O
2700	O
watts	O
on	O
a	O
single	O
printed	O
circuit	O
board	O
while	O
maintaining	O
chip	O
temperature	O
at	O
.	O
</s>
<s>
Thermal	B-General_Concept
conduction	I-General_Concept
modules	I-General_Concept
using	O
water	O
cooling	O
were	O
also	O
used	O
in	O
mainframe	B-Architecture
systems	O
manufactured	O
by	O
other	O
companies	O
including	O
Mitsubishi	O
and	O
Fujitsu	O
.	O
</s>
<s>
The	O
Cray-1	B-Device
supercomputer	B-Architecture
designed	O
in	O
1976	O
had	O
a	O
distinctive	O
cooling	O
system	O
.	O
</s>
<s>
The	O
integrated	O
circuits	O
used	O
in	O
the	O
machine	O
were	O
the	O
fastest	O
available	O
at	O
the	O
time	O
,	O
using	O
emitter-coupled	B-General_Concept
logic	I-General_Concept
;	O
however	O
,	O
the	O
speed	O
was	O
accompanied	O
by	O
high	O
power	O
consumption	O
compared	O
to	O
later	O
CMOS	B-Device
devices	O
.	O
</s>
<s>
Recent	O
supercomputer	B-Architecture
projects	O
such	O
as	O
Blue	B-Operating_System
Gene	I-Operating_System
rely	O
on	O
air	O
cooling	O
,	O
which	O
reduces	O
cost	O
,	O
complexity	O
,	O
and	O
size	O
of	O
systems	O
compared	O
to	O
liquid	O
cooling	O
.	O
</s>
<s>
Fans	O
may	O
be	O
fitted	O
to	O
the	O
computer	B-General_Concept
case	I-General_Concept
or	O
attached	O
to	O
CPUs	O
,	O
GPUs	B-Architecture
,	O
chipsets	B-Device
,	O
power	O
supply	O
units	O
(	O
PSUs	O
)	O
,	O
hard	B-Device
drives	I-Device
,	O
or	O
as	O
cards	O
plugged	O
into	O
an	O
expansion	O
slot	O
.	O
</s>
<s>
Common	O
fan	B-Application
sizes	O
include	O
40	O
,	O
60	O
,	O
80	O
,	O
92	O
,	O
120	O
,	O
and	O
140mm	O
.	O
</s>
<s>
Free	O
air	O
flow	O
is	O
the	O
amount	O
of	O
air	O
a	O
fan	B-Application
will	O
move	O
with	O
zero	O
back-pressure	O
.	O
</s>
<s>
Maximum	O
differential	O
pressure	O
is	O
the	O
amount	O
of	O
pressure	O
a	O
fan	B-Application
can	O
generate	O
when	O
completely	O
blocked	O
.	O
</s>
<s>
Each	O
fan	B-Application
model	O
will	O
have	O
a	O
unique	O
curve	O
,	O
like	O
the	O
dashed	O
curves	O
in	O
the	O
adjacent	O
illustration	O
.	O
</s>
<s>
Series	O
installation	O
would	O
be	O
a	O
second	O
fan	B-Application
in	O
line	O
with	O
another	O
fan	B-Application
such	O
as	O
an	O
inlet	O
fan	B-Application
and	O
an	O
exhaust	O
fan	B-Application
.	O
</s>
<s>
The	O
adjacent	O
illustration	O
shows	O
a	O
single	O
fan	B-Application
versus	O
two	O
fans	O
in	O
parallel	O
with	O
a	O
maximum	O
pressure	O
of	O
of	O
water	O
and	O
a	O
doubled	O
flow	O
rate	O
of	O
about	O
.	O
</s>
<s>
With	O
the	O
chassis	O
impedance	O
curve	O
(	O
represented	O
by	O
the	O
solid	O
red	O
and	O
black	O
lines	O
on	O
the	O
adjacent	O
curve	O
)	O
determined	O
,	O
the	O
actual	O
flow	O
through	O
the	O
chassis	O
as	O
generated	O
by	O
a	O
particular	O
fan	B-Application
configuration	O
is	O
graphically	O
shown	O
where	O
the	O
chassis	O
impedance	O
curve	O
crosses	O
the	O
fan	B-Application
curve	O
.	O
</s>
<s>
In	O
this	O
particular	O
example	O
,	O
adding	O
a	O
second	O
fan	B-Application
provided	O
marginal	O
improvement	O
with	O
the	O
flow	O
for	O
both	O
configurations	O
being	O
approximately	O
.	O
</s>
<s>
While	O
not	O
shown	O
on	O
the	O
plot	O
,	O
a	O
second	O
fan	B-Application
in	O
series	O
would	O
provide	O
slightly	O
better	O
performance	O
than	O
the	O
parallel	O
installation	O
.	O
</s>
<s>
This	O
would	O
be	O
actual	O
flow	O
through	O
the	O
chassis	O
and	O
not	O
the	O
free	O
air	O
rating	O
of	O
the	O
fan	B-Application
.	O
</s>
<s>
It	O
should	O
also	O
be	O
noted	O
that	O
"	O
Q	O
"	O
,	O
the	O
heat	O
transferred	O
,	O
is	O
a	O
function	O
of	O
the	O
heat	O
transfer	O
efficiency	O
of	O
a	O
CPU	B-General_Concept
or	O
GPU	B-Architecture
cooler	O
to	O
the	O
airflow	O
.	O
</s>
<s>
The	O
jet	O
can	O
move	O
the	O
same	O
amount	O
of	O
air	O
as	O
a	O
cooling	O
fan	B-Application
twice	O
its	O
size	O
while	O
consuming	O
half	O
as	O
much	O
electricity	O
and	O
at	O
lower	O
cost	O
.	O
</s>
<s>
More	O
commonly	O
for	O
a	O
personal	O
computer	O
CPU	B-General_Concept
,	O
a	O
clamp	O
holds	O
the	O
heatsink	O
directly	O
over	O
the	O
chip	O
,	O
with	O
a	O
thermal	O
grease	O
or	O
thermal	O
pad	O
spread	O
between	O
.	O
</s>
<s>
The	O
heat	O
conductivity	O
of	O
metal	O
is	O
much	O
better	O
than	O
that	O
of	O
air	O
,	O
and	O
it	O
radiates	O
heat	O
better	O
than	O
the	O
component	O
that	O
it	O
is	O
protecting	O
(	O
usually	O
an	O
integrated	O
circuit	O
or	O
CPU	B-General_Concept
)	O
.	O
</s>
<s>
Fan-cooled	O
aluminium	O
heatsinks	O
were	O
originally	O
the	O
norm	O
for	O
desktop	B-Device
computers	I-Device
,	O
but	O
nowadays	O
many	O
heatsinks	O
feature	O
copper	O
base-plates	O
or	O
are	O
entirely	O
made	O
of	O
copper	O
.	O
</s>
<s>
Passive	O
heatsinks	O
are	O
commonly	O
found	O
on	O
older	O
CPUs	O
,	O
parts	O
that	O
do	O
not	O
get	O
very	O
hot	O
(	O
such	O
as	O
the	O
chipset	B-Device
)	O
,	O
and	O
low-power	O
computers	O
.	O
</s>
<s>
Usually	O
a	O
heatsink	O
is	O
attached	O
to	O
the	O
integrated	O
heat	O
spreader	O
(	O
IHS	O
)	O
,	O
essentially	O
a	O
large	O
,	O
flat	O
plate	O
attached	O
to	O
the	O
CPU	B-General_Concept
,	O
with	O
conduction	O
paste	O
layered	O
between	O
.	O
</s>
<s>
In	O
addition	O
,	O
the	O
IHS	O
protects	O
the	O
fragile	O
CPU	B-General_Concept
.	O
</s>
<s>
Passive	O
cooling	O
involves	O
no	O
fan	B-Application
noise	O
as	O
convection	O
forces	O
move	O
air	O
over	O
the	O
heatsink	O
.	O
</s>
<s>
Another	O
growing	O
trend	O
due	O
to	O
the	O
increasing	O
heat	O
density	O
of	O
computers	O
,	O
GPUs	B-Architecture
,	O
FPGAs	O
,	O
and	O
ASICs	O
is	O
to	O
immerse	O
the	O
entire	O
computer	O
or	O
select	O
components	O
in	O
a	O
thermally	O
,	O
but	O
not	O
electrically	O
,	O
conductive	O
liquid	O
.	O
</s>
<s>
It	O
is	O
also	O
becoming	O
popular	O
with	O
data	B-Operating_System
centers	I-Operating_System
.	O
</s>
<s>
Personal	O
computers	O
cooled	O
in	O
this	O
manner	O
may	O
not	O
require	O
either	O
fans	O
or	O
pumps	O
,	O
and	O
may	O
be	O
cooled	O
exclusively	O
by	O
passive	O
heat	O
exchange	O
between	O
the	O
computer	B-Architecture
hardware	I-Architecture
and	O
the	O
enclosure	O
it	O
is	O
placed	O
in	O
.	O
</s>
<s>
Thermal	O
pastes	O
used	O
to	O
transfer	O
heat	O
to	O
heatsinks	O
from	O
processors	O
and	O
graphic	B-Device
cards	I-Device
has	O
been	O
reported	O
to	O
dissolve	O
in	O
some	O
liquids	O
,	O
however	O
with	O
negligible	O
impact	O
to	O
cooling	O
,	O
unless	O
the	O
components	O
were	O
removed	O
and	O
operated	O
in	O
air	O
.	O
</s>
<s>
Immersion	O
cooling	O
can	O
allow	O
for	O
extremely	O
low	O
PUE	O
values	O
of	O
1.05	O
,	O
vs	O
air	O
cooling	O
's	O
1.35	O
,	O
and	O
allow	O
for	O
up	O
to	O
100KW	O
of	O
computing	O
power	O
(	O
heat	O
dissipation	O
,	O
TDP	O
)	O
per	O
19-inch	B-Application
rack	I-Application
,	O
as	O
opposed	O
to	O
air	O
cooling	O
,	O
which	O
usually	O
handles	O
up	O
to	O
23KW	O
.	O
</s>
<s>
a	O
VIA	B-Device
EPIA	I-Device
motherboard	B-Device
with	O
CPU	B-General_Concept
typically	O
dissipates	O
approximately	O
25watts	O
of	O
heat	O
,	O
whereas	O
a	O
more	O
capable	O
Pentium	O
4	O
motherboard	B-Device
and	O
CPU	B-General_Concept
typically	O
dissipates	O
around	O
140watts	O
.	O
</s>
<s>
Computers	O
can	O
be	O
powered	O
with	O
direct	O
current	O
from	O
an	O
external	O
power	O
supply	O
unit	O
which	O
does	O
not	O
generate	O
heat	O
inside	O
the	O
computer	B-General_Concept
case	I-General_Concept
.	O
</s>
<s>
The	O
replacement	O
of	O
cathode	B-Device
ray	I-Device
tube	I-Device
(	O
CRT	O
)	O
displays	O
by	O
more	O
efficient	O
thin-screen	O
liquid	B-Device
crystal	I-Device
display	I-Device
(	O
LCD	B-Device
)	O
ones	O
in	O
the	O
early	O
twenty-first	O
century	O
has	O
reduced	O
power	O
consumption	O
significantly	O
.	O
</s>
<s>
Heat	O
is	O
carried	O
away	O
from	O
the	O
heatsink	O
by	O
convective	O
or	O
fan-forced	O
airflow	O
.	O
</s>
<s>
Fan	B-Application
cooling	O
is	O
often	O
used	O
to	O
cool	O
processors	O
and	O
graphics	B-Device
cards	I-Device
that	O
consume	O
significant	O
amounts	O
of	O
electrical	O
energy	O
.	O
</s>
<s>
A	O
block	O
of	O
metal	O
with	O
a	O
corresponding	O
flat	O
surface	O
and	O
finned	O
construction	O
,	O
sometimes	O
with	O
an	O
attached	O
fan	B-Application
,	O
is	O
clamped	O
to	O
the	O
component	O
.	O
</s>
<s>
Heat	O
is	O
removed	O
from	O
the	O
heatsink	O
by	O
convection	O
,	O
to	O
some	O
extent	O
by	O
radiation	B-Algorithm
,	O
and	O
possibly	O
by	O
conduction	O
if	O
the	O
heatsink	O
is	O
in	O
thermal	O
contact	O
with	O
,	O
say	O
,	O
the	O
metal	O
case	O
.	O
</s>
<s>
Inexpensive	O
fan-cooled	O
aluminium	O
heatsinks	O
are	O
often	O
used	O
on	O
standard	O
desktop	B-Device
computers	I-Device
.	O
</s>
<s>
A	O
copper	O
heatsink	O
is	O
more	O
effective	O
than	O
an	O
aluminium	O
unit	O
of	O
the	O
same	O
size	O
,	O
which	O
is	O
relevant	O
with	O
regard	O
to	O
the	O
high-power-consumption	O
components	O
used	O
in	O
high-performance	B-Architecture
computers	I-Architecture
.	O
</s>
<s>
Passive	O
heatsinks	O
are	O
commonly	O
found	O
on	O
older	O
CPUs	O
,	O
parts	O
that	O
do	O
not	O
dissipate	O
much	O
power	O
(	O
such	O
as	O
the	O
chipset	B-Device
)	O
,	O
computers	O
with	O
low-power	O
processors	O
,	O
and	O
equipment	O
where	O
silent	O
operation	O
is	O
critical	O
and	O
fan	B-Application
noise	O
unacceptable	O
.	O
</s>
<s>
Usually	O
a	O
heatsink	O
is	O
clamped	O
to	O
the	O
integrated	O
heat	O
spreader	O
(	O
IHS	O
)	O
,	O
a	O
flat	O
metal	O
plate	O
the	O
size	O
of	O
the	O
CPU	B-General_Concept
package	O
which	O
is	O
part	O
of	O
the	O
CPU	B-General_Concept
assembly	O
and	O
spreads	O
the	O
heat	O
locally	O
.	O
</s>
<s>
The	O
same	O
technique	O
is	O
used	O
for	O
video	B-Device
cards	I-Device
that	O
use	O
a	O
finned	O
passive	O
heatsink	O
on	O
the	O
GPU	B-Architecture
.	O
</s>
<s>
A	O
combination	O
of	O
bismuth	B-Algorithm
and	O
tellurium	O
is	O
most	O
commonly	O
used	O
for	O
the	O
thermocouples	O
.	O
</s>
<s>
It	O
is	O
also	O
possible	O
to	O
use	O
a	O
Peltier	O
element	O
together	O
with	O
a	O
high	O
pressure	O
refrigerant	O
(	O
two	O
phase	O
cooling	O
)	O
to	O
cool	O
the	O
CPU	B-General_Concept
.	O
</s>
<s>
Liquid	O
cooling	O
is	O
a	O
highly	O
effective	O
method	O
of	O
removing	O
excess	O
heat	O
,	O
with	O
the	O
most	O
common	O
heat	O
transfer	O
fluid	O
in	O
desktop	B-Device
PCs	I-Device
being	O
(	O
distilled	O
)	O
water	O
.	O
</s>
<s>
The	O
principle	O
used	O
in	O
a	O
typical	O
(	O
active	O
)	O
liquid	O
cooling	O
system	O
for	O
computers	O
is	O
identical	O
to	O
that	O
used	O
in	O
an	O
automobile	O
's	O
internal	O
combustion	O
engine	O
,	O
with	O
the	O
water	O
being	O
circulated	O
by	O
a	O
water	O
pump	O
through	O
a	O
water	B-Device
block	I-Device
mounted	O
on	O
the	O
CPU	B-General_Concept
(	O
and	O
sometimes	O
additional	O
components	O
as	O
GPU	B-Architecture
and	O
northbridge	B-Device
)	O
and	O
out	O
to	O
a	O
heat	O
exchanger	O
,	O
typically	O
a	O
radiator	O
.	O
</s>
<s>
The	O
radiator	O
is	O
itself	O
usually	O
cooled	O
additionally	O
by	O
means	O
of	O
a	O
fan	B-Application
.	O
</s>
<s>
Besides	O
a	O
fan	B-Application
,	O
it	O
could	O
possibly	O
also	O
be	O
cooled	O
by	O
other	O
means	O
,	O
such	O
as	O
a	O
Peltier	O
cooler	O
(	O
although	O
Peltier	O
elements	O
are	O
most	O
commonly	O
placed	O
directly	O
on	O
top	O
of	O
the	O
hardware	B-Architecture
to	O
be	O
cooled	O
,	O
and	O
the	O
coolant	O
is	O
used	O
to	O
conduct	O
the	O
heat	O
away	O
from	O
the	O
hot	O
side	O
of	O
the	O
Peltier	O
element	O
)	O
.	O
</s>
<s>
These	O
systems	O
often	O
leave	O
out	O
a	O
fan	B-Application
or	O
a	O
water	O
pump	O
,	O
theoretically	O
increasing	O
their	O
reliability	O
and	O
making	O
them	O
quieter	O
than	O
active	O
systems	O
.	O
</s>
<s>
Liquids	O
allow	O
the	O
transfer	O
of	O
more	O
heat	O
from	O
the	O
parts	O
being	O
cooled	O
than	O
air	O
,	O
making	O
liquid	O
cooling	O
suitable	O
for	O
overclocking	B-Application
and	O
high	B-Architecture
performance	I-Architecture
computer	I-Architecture
applications	O
.	O
</s>
<s>
(	O
The	O
first	O
major	O
foray	O
into	O
the	O
field	O
of	O
liquid-cooled	O
personal	O
computers	O
for	O
general	O
use	O
,	O
the	O
high-end	O
versions	O
of	O
Apple	O
's	O
Power	B-Device
Mac	I-Device
G5	I-Device
,	O
was	O
ultimately	O
doomed	O
by	O
a	O
propensity	O
for	O
coolant	O
leaks	O
.	O
)	O
</s>
<s>
An	O
air-cooled	O
heatsink	O
is	O
generally	O
much	O
simpler	O
to	O
build	O
,	O
install	O
,	O
and	O
maintain	O
than	O
a	O
water	O
cooling	O
solution	O
,	O
although	O
CPU-specific	O
water	O
cooling	O
kits	O
can	O
also	O
be	O
found	O
,	O
which	O
may	O
be	O
just	O
as	O
easy	O
to	O
install	O
as	O
an	O
air	O
cooler	O
.	O
</s>
<s>
These	O
are	O
not	O
limited	O
to	O
CPUs	O
,	O
and	O
liquid	O
cooling	O
of	O
GPU	B-Architecture
cards	O
is	O
also	O
possible	O
.	O
</s>
<s>
While	O
originally	O
limited	O
to	O
mainframe	B-Architecture
computers	I-Architecture
,	O
liquid	O
cooling	O
has	O
become	O
a	O
practice	O
largely	O
associated	O
with	O
overclocking	B-Application
in	O
the	O
form	O
of	O
either	O
manufactured	O
all-in-one	O
(	O
AIO	O
)	O
kits	O
or	O
do-it-yourself	O
setups	O
assembled	O
from	O
individually	O
gathered	O
parts	O
.	O
</s>
<s>
The	O
past	O
few	O
years	O
have	O
seen	O
an	O
increase	O
in	O
the	O
popularity	O
of	O
liquid	O
cooling	O
in	O
pre-assembled	O
,	O
moderate	O
to	O
high	O
performance	O
,	O
desktop	B-Device
computers	I-Device
.	O
</s>
<s>
Sealed	O
(	O
"	O
closed-loop	O
"	O
)	O
systems	O
incorporating	O
a	O
small	O
pre-filled	O
radiator	O
,	O
fan	B-Application
,	O
and	O
waterblock	B-Device
simplify	O
the	O
installation	O
and	O
maintenance	O
of	O
water	O
cooling	O
at	O
a	O
slight	O
cost	O
in	O
cooling	O
effectiveness	O
relative	O
to	O
larger	O
and	O
more	O
complex	O
setups	O
.	O
</s>
<s>
Liquid	O
cooling	O
is	O
typically	O
combined	O
with	O
air	O
cooling	O
,	O
using	O
liquid	O
cooling	O
for	O
the	O
hottest	O
components	O
,	O
such	O
as	O
CPUs	O
or	O
GPUs	B-Architecture
,	O
while	O
retaining	O
the	O
simpler	O
and	O
cheaper	O
air	O
cooling	O
for	O
less	O
demanding	O
components	O
.	O
</s>
<s>
For	O
use	O
in	O
computers	O
,	O
the	O
heatsink	O
on	O
the	O
CPU	B-General_Concept
is	O
attached	O
to	O
a	O
larger	O
radiator	O
heatsink	O
.	O
</s>
<s>
Both	O
heatsinks	O
are	O
hollow	O
,	O
as	O
is	O
the	O
attachment	O
between	O
them	O
,	O
creating	O
one	O
large	O
heat	O
pipe	O
that	O
transfers	O
heat	O
from	O
the	O
CPU	B-General_Concept
to	O
the	O
radiator	O
,	O
which	O
is	O
then	O
cooled	O
using	O
some	O
conventional	O
method	O
.	O
</s>
<s>
This	O
method	O
is	O
usually	O
used	O
when	O
space	O
is	O
tight	O
,	O
as	O
in	O
small	O
form-factor	O
PCs	O
and	O
laptops	O
,	O
or	O
where	O
no	O
fan	B-Application
noise	O
can	O
be	O
tolerated	O
,	O
as	O
in	O
audio	O
production	O
.	O
</s>
<s>
Because	O
of	O
the	O
efficiency	O
of	O
this	O
method	O
of	O
cooling	O
,	O
many	O
desktop	O
CPUs	O
and	O
GPUs	B-Architecture
,	O
as	O
well	O
as	O
high	O
end	O
chipsets	B-Device
,	O
use	O
heat	O
pipes	O
or	O
vapor	O
chambers	O
in	O
addition	O
to	O
active	O
fan-based	O
cooling	O
and	O
passive	O
heatsinks	O
to	O
remain	O
within	O
safe	O
operating	O
temperatures	O
.	O
</s>
<s>
Vapor	O
chambers	O
may	O
also	O
be	O
used	O
on	O
high-end	O
smartphones	B-Application
.	O
</s>
<s>
The	O
corona	O
discharge	O
cooler	O
developed	O
by	O
Kronos	O
works	O
in	O
the	O
following	O
manner	O
:	O
A	O
high	O
electric	O
field	O
is	O
created	O
at	O
the	O
tip	O
of	O
the	O
cathode	O
,	O
which	O
is	O
placed	O
on	O
one	O
side	O
of	O
the	O
CPU	B-General_Concept
.	O
</s>
<s>
Placing	O
a	O
grounded	O
anode	O
at	O
the	O
opposite	O
end	O
of	O
the	O
CPU	B-General_Concept
causes	O
the	O
charged	O
ions	O
in	O
the	O
corona	O
to	O
accelerate	O
towards	O
the	O
anode	O
,	O
colliding	O
with	O
neutral	O
air	O
molecules	O
on	O
the	O
way	O
.	O
</s>
<s>
Soft	O
cooling	O
is	O
the	O
practice	O
of	O
utilizing	O
software	O
to	O
take	O
advantage	O
of	O
CPU	B-General_Concept
power	O
saving	O
technologies	O
to	O
minimize	O
energy	O
use	O
.	O
</s>
<s>
This	O
is	O
done	O
using	O
halt	B-Language
instructions	O
to	O
turn	O
off	O
or	O
put	O
in	O
standby	O
state	O
CPU	B-General_Concept
subparts	O
that	O
are	O
n't	O
being	O
used	O
or	O
by	O
underclocking	B-Device
the	O
CPU	B-General_Concept
.	O
</s>
<s>
While	O
resulting	O
in	O
lower	O
total	O
speeds	O
,	O
this	O
can	O
be	O
very	O
useful	O
if	O
overclocking	B-Application
a	O
CPU	B-General_Concept
to	O
improve	O
user	B-Application
experience	I-Application
rather	O
than	O
increase	O
raw	O
processing	O
power	O
,	O
since	O
it	O
can	O
prevent	O
the	O
need	O
for	O
noisier	O
cooling	O
.	O
</s>
<s>
Undervolting	O
is	O
a	O
practice	O
of	O
running	O
the	O
CPU	B-General_Concept
or	O
any	O
other	O
component	O
with	O
voltages	O
below	O
the	O
device	O
specifications	O
.	O
</s>
<s>
This	O
tolerance	O
ensures	O
that	O
the	O
processor	O
will	O
have	O
a	O
higher	O
chance	O
of	O
performing	O
correctly	O
under	O
sub-optimal	O
conditions	O
,	O
such	O
as	O
a	O
lower-quality	O
motherboard	B-Device
or	O
low	O
power	O
supply	O
voltages	O
.	O
</s>
<s>
Below	O
a	O
certain	O
limit	O
,	O
the	O
processor	O
will	O
not	O
function	O
correctly	O
,	O
although	O
undervolting	O
too	O
far	O
does	O
not	O
typically	O
lead	O
to	O
permanent	O
hardware	B-Architecture
damage	O
(	O
unlike	O
overvolting	O
)	O
.	O
</s>
<s>
At	O
these	O
locations	O
,	O
power	O
dissipation	O
of	O
over	O
300W/cm2	O
(	O
typical	O
CPU	B-General_Concept
is	O
less	O
than	O
100W/cm2	O
)	O
can	O
occur	O
,	O
although	O
future	O
systems	O
are	O
expected	O
to	O
exceed	O
1000W/cm2	O
.	O
</s>
<s>
In	O
micro-channel	O
heatsinks	O
,	O
channels	O
are	O
fabricated	O
into	O
the	O
silicon	O
chip	O
(	O
CPU	B-General_Concept
)	O
,	O
and	O
coolant	O
is	O
pumped	O
through	O
them	O
.	O
</s>
<s>
The	O
jet	O
is	O
directed	O
toward	O
the	O
surface	O
of	O
the	O
CPU	B-General_Concept
chip	O
,	O
and	O
can	O
effectively	O
remove	O
large	O
heat	O
fluxes	O
.	O
</s>
<s>
The	O
compressor	O
compresses	O
a	O
gas	O
(	O
or	O
mixture	O
of	O
gases	O
)	O
which	O
comes	O
from	O
the	O
evaporator	O
(	O
CPU	B-General_Concept
cooler	I-General_Concept
discussed	O
below	O
)	O
.	O
</s>
<s>
The	O
liquid	O
flows	O
into	O
the	O
evaporator	O
cooling	O
the	O
CPU	B-General_Concept
,	O
turning	O
into	O
a	O
vapor	O
at	O
low	O
pressure	O
.	O
</s>
<s>
The	O
larger	O
chamber	O
is	O
as	O
close	O
to	O
the	O
heat	O
source	O
and	O
designed	O
to	O
conduct	O
as	O
much	O
heat	O
from	O
it	O
into	O
the	O
liquid	O
as	O
possible	O
,	O
for	O
example	O
,	O
a	O
CPU	B-General_Concept
cold	O
plate	O
with	O
the	O
chamber	O
inside	O
it	O
filled	O
with	O
the	O
liquid	O
.	O
</s>
<s>
One	O
or	O
more	O
pipes	O
extend	O
upward	O
into	O
some	O
sort	O
of	O
radiator	O
or	O
similar	O
heat	O
dissipation	O
area	O
,	O
and	O
this	O
is	O
all	O
set	O
up	O
such	O
that	O
the	O
CPU	B-General_Concept
heats	O
the	O
reservoir	O
and	O
liquid	O
it	O
contains	O
,	O
which	O
begins	O
boiling	O
,	O
and	O
the	O
vapor	O
travels	O
up	O
the	O
tube(s )	O
into	O
the	O
radiator/heat	O
dissipation	O
area	O
,	O
and	O
then	O
after	O
condensing	O
,	O
drips	O
back	O
down	O
into	O
the	O
reservoir	O
,	O
or	O
runs	O
down	O
the	O
sides	O
of	O
the	O
tube	O
.	O
</s>
<s>
As	O
liquid	O
nitrogen	O
boils	O
at	O
,	O
far	O
below	O
the	O
freezing	O
point	O
of	O
water	O
,	O
it	O
is	O
valuable	O
as	O
an	O
extreme	O
coolant	O
for	O
short	O
overclocking	B-Application
sessions	O
.	O
</s>
<s>
In	O
a	O
typical	O
installation	O
of	O
liquid	O
nitrogen	O
cooling	O
,	O
a	O
copper	O
or	O
aluminium	O
pipe	O
is	O
mounted	O
on	O
top	O
of	O
the	O
processor	O
or	O
graphics	B-Device
card	I-Device
.	O
</s>
<s>
In	O
the	O
realm	O
of	O
personal	O
computers	O
,	O
this	O
method	O
of	O
cooling	O
is	O
seldom	O
used	O
in	O
contexts	O
other	O
than	O
overclocking	B-Application
trial-runs	O
and	O
record-setting	O
attempts	O
,	O
as	O
the	O
CPU	B-General_Concept
will	O
usually	O
expire	O
within	O
a	O
relatively	O
short	O
period	O
of	O
time	O
due	O
to	O
temperature	O
stress	O
caused	O
by	O
changes	O
in	O
internal	O
temperature	O
.	O
</s>
<s>
Liquid	O
nitrogen	O
cooling	O
is	O
,	O
generally	O
,	O
only	O
used	O
for	O
processor	O
benchmarking	O
,	O
due	O
to	O
the	O
fact	O
that	O
continuous	O
usage	O
may	O
cause	O
permanent	O
damage	O
to	O
one	O
or	O
more	O
parts	O
of	O
the	O
computer	O
and	O
,	O
if	O
handled	O
in	O
a	O
careless	O
way	O
,	O
can	O
even	O
harm	O
the	O
user	O
,	O
causing	O
frostbite	B-Operating_System
.	O
</s>
<s>
These	O
techniques	O
are	O
often	O
used	O
,	O
in	O
particular	O
,	O
by	O
those	O
who	O
run	O
parts	O
of	O
their	O
computer	O
(	O
such	O
as	O
the	O
CPU	B-General_Concept
and	O
GPU	B-Architecture
)	O
at	O
higher	O
voltages	O
and	O
frequencies	O
than	O
specified	O
by	O
manufacturer	O
(	O
overclocking	B-Application
)	O
,	O
which	O
increases	O
heat	O
generation	O
.	O
</s>
<s>
The	O
installation	O
of	O
higher	O
performance	O
,	O
non-stock	O
cooling	O
may	O
also	O
be	O
considered	O
modding	B-Device
.	O
</s>
<s>
Many	O
overclockers	B-Application
simply	O
buy	O
more	O
efficient	O
,	O
and	O
often	O
,	O
more	O
expensive	O
fan	B-Application
and	O
heatsink	O
combinations	O
,	O
while	O
others	O
resort	O
to	O
more	O
exotic	O
ways	O
of	O
computer	B-General_Concept
cooling	I-General_Concept
,	O
such	O
as	O
liquid	O
cooling	O
,	O
Peltier	O
effect	O
heatpumps	O
,	O
heat	O
pipe	O
or	O
phase	O
change	O
cooling	O
.	O
</s>
<s>
There	O
is	O
much	O
debate	O
about	O
the	O
merits	O
of	O
compounds	O
,	O
and	O
overclockers	B-Application
often	O
consider	O
some	O
compounds	O
to	O
be	O
superior	O
to	O
others	O
.	O
</s>
<s>
Mass-produced	O
CPU	B-General_Concept
heat	O
spreaders	O
and	O
heatsink	O
bases	O
are	O
never	O
perfectly	O
flat	O
or	O
smooth	O
;	O
if	O
these	O
surfaces	O
are	O
placed	O
in	O
the	O
best	O
contact	O
possible	O
,	O
there	O
will	O
be	O
air	O
gaps	O
which	O
reduce	O
heat	O
conduction	O
.	O
</s>
<s>
This	O
can	O
be	O
achieved	O
by	O
a	O
laborious	O
process	O
known	O
as	O
lapping	O
,	O
which	O
can	O
reduce	O
CPU	B-General_Concept
temperature	O
by	O
typically	O
.	O
</s>
<s>
Most	O
older	O
PCs	O
use	O
flat	O
ribbon	O
cables	O
to	O
connect	O
storage	O
drives	O
(	O
IDE	B-Protocol
or	O
SCSI	B-Architecture
)	O
.	O
</s>
<s>
Overclockers	B-Application
and	O
modders	B-Device
often	O
replace	O
these	O
with	O
rounded	O
cables	O
,	O
with	O
the	O
conductive	O
wires	O
bunched	O
together	O
tightly	O
to	O
reduce	O
surface	O
area	O
.	O
</s>
<s>
Examples	O
are	O
air	O
snorkels	O
and	O
tunnels	O
that	O
feed	O
outside	O
air	O
directly	O
and	O
exclusively	O
to	O
the	O
CPU	B-General_Concept
or	O
GPU	B-Architecture
cooler	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
BTX	B-Device
case	O
design	O
prescribes	O
a	O
CPU	B-General_Concept
air	O
tunnel	O
.	O
</s>
<s>
Examples	O
are	O
:	O
Conventional	O
PC	O
(	O
ATX	B-Language
)	O
power	O
supplies	O
blow	O
the	O
warm	O
air	O
out	O
the	O
back	O
of	O
the	O
case	O
.	O
</s>
<s>
Many	O
dual-slot	O
graphics	B-Device
card	I-Device
designs	O
blow	O
the	O
warm	O
air	O
through	O
the	O
cover	O
of	O
the	O
adjacent	O
slot	O
.	O
</s>
<s>
Some	O
CPU	B-General_Concept
cooling	I-General_Concept
designs	O
blow	O
the	O
warm	O
air	O
directly	O
towards	O
the	O
back	O
of	O
the	O
case	O
,	O
where	O
it	O
can	O
be	O
ejected	O
by	O
a	O
case	B-Application
fan	I-Application
.	O
</s>
<s>
The	O
BTX	B-Device
case	O
design	O
violates	O
this	O
rule	O
,	O
since	O
it	O
uses	O
the	O
CPU	B-General_Concept
cooler	I-General_Concept
's	O
exhaust	O
to	O
cool	O
the	O
chipset	B-Device
and	O
often	O
the	O
graphics	B-Device
card	I-Device
.	O
</s>
<s>
One	O
may	O
come	O
across	O
old	O
or	O
ultra-low-budget	O
ATX	B-Language
cases	O
which	O
feature	O
a	O
PSU	O
mount	O
in	O
the	O
top	O
.	O
</s>
<s>
Most	O
modern	O
ATX	B-Language
cases	O
do	O
however	O
have	O
a	O
PSU	O
mount	O
in	O
the	O
bottom	O
of	O
the	O
case	O
with	O
a	O
filtered	O
air	O
vent	O
directly	O
beneath	O
the	O
PSU	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
CPU	B-General_Concept
cooling	I-General_Concept
air	O
duct	O
at	O
the	O
back	O
of	O
a	O
tower	O
case	O
would	O
inhale	O
warm	O
air	O
from	O
a	O
graphics	B-Device
card	I-Device
exhaust	O
.	O
</s>
<s>
Hiding	O
cables	O
behind	O
motherboard	B-Device
tray	O
or	O
simply	O
apply	O
ziptie	O
and	O
tucking	O
cables	O
away	O
to	O
provide	O
unhindered	O
airflow	O
.	O
</s>
<s>
There	O
is	O
little	O
agreement	O
on	O
the	O
effectiveness	O
of	O
different	O
fan	B-Application
placement	O
configurations	O
,	O
and	O
little	O
in	O
the	O
way	O
of	O
systematic	O
testing	O
has	O
been	O
done	O
.	O
</s>
<s>
For	O
a	O
rectangular	O
PC	O
(	O
ATX	B-Language
)	O
case	O
,	O
a	O
fan	B-Application
in	O
the	O
front	O
with	O
a	O
fan	B-Application
in	O
the	O
rear	O
and	O
one	O
in	O
the	O
top	O
has	O
been	O
found	O
to	O
be	O
a	O
suitable	O
configuration	O
.	O
</s>
<s>
However	O
,	O
AMD	O
's	O
(	O
somewhat	O
outdated	O
)	O
system	O
cooling	O
guidelines	O
notes	O
that	O
"	O
A	O
front	O
cooling	O
fan	B-Application
does	O
not	O
seem	O
to	O
be	O
essential	O
.	O
</s>
<s>
Desktop	B-Device
computers	I-Device
typically	O
use	O
one	O
or	O
more	O
fans	O
for	O
cooling	O
.	O
</s>
<s>
While	O
almost	O
all	O
desktop	O
power	O
supplies	O
have	O
at	O
least	O
one	O
built-in	O
fan	B-Application
,	O
power	O
supplies	O
should	O
never	O
draw	O
heated	O
air	O
from	O
within	O
the	O
case	O
,	O
as	O
this	O
results	O
in	O
higher	O
PSU	O
operating	O
temperatures	O
which	O
decrease	O
the	O
PSU	O
's	O
energy	O
efficiency	O
,	O
reliability	O
and	O
overall	O
ability	O
to	O
provide	O
a	O
steady	O
supply	O
of	O
power	O
to	O
the	O
computer	O
's	O
internal	O
components	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
all	O
modern	O
ATX	B-Language
cases	O
(	O
with	O
some	O
exceptions	O
found	O
in	O
ultra-low-budget	O
cases	O
)	O
feature	O
a	O
power	O
supply	O
mount	O
in	O
the	O
bottom	O
,	O
with	O
a	O
dedicated	O
PSU	O
air	O
intake	O
(	O
often	O
with	O
its	O
own	O
filter	O
)	O
beneath	O
the	O
mounting	O
location	O
,	O
allowing	O
the	O
PSU	O
to	O
draw	O
cool	O
air	O
from	O
beneath	O
the	O
case	O
.	O
</s>
<s>
The	O
air	O
flow	O
inside	O
the	O
typical	O
desktop	B-General_Concept
case	I-General_Concept
is	O
usually	O
not	O
strong	O
enough	O
for	O
a	O
passive	O
CPU	B-General_Concept
heatsink	O
.	O
</s>
<s>
Each	O
server	O
can	O
have	O
an	O
independent	O
internal	O
cooler	O
system	O
;	O
Server	B-General_Concept
cooling	I-General_Concept
fans	O
in	O
(	O
1	O
U	O
)	O
enclosures	O
are	O
usually	O
located	O
in	O
the	O
middle	O
of	O
the	O
enclosure	O
,	O
between	O
the	O
hard	B-Device
drives	I-Device
at	O
the	O
front	O
and	O
passive	O
CPU	B-General_Concept
heatsinks	O
at	O
the	O
rear	O
.	O
</s>
<s>
Rack	B-Application
cabinet	I-Application
is	O
a	O
typical	O
enclosure	O
for	O
horizontally	O
mounted	O
servers	O
.	O
</s>
<s>
Each	O
cabinet	O
can	O
have	O
additional	O
cooling	O
options	O
;	O
for	O
example	O
,	O
they	O
can	O
have	O
a	O
Close	O
Coupled	O
Cooling	O
attachable	O
module	O
or	O
integrated	O
with	O
cabinet	O
elements	O
(	O
like	O
cooling	O
doors	O
in	O
iDataPlex	O
server	B-Application
rack	I-Application
)	O
.	O
</s>
<s>
Another	O
way	O
of	O
accommodating	O
large	O
numbers	O
of	O
systems	O
in	O
a	O
small	O
space	O
is	O
to	O
use	O
blade	B-Architecture
chassis	I-Architecture
,	O
oriented	O
vertically	O
rather	O
than	O
horizontally	O
,	O
to	O
facilitate	O
convection	O
.	O
</s>
<s>
Because	O
data	B-Operating_System
centers	I-Operating_System
typically	O
contain	O
large	O
numbers	O
of	O
computers	O
and	O
other	O
power-dissipating	O
devices	O
,	O
they	O
risk	O
equipment	O
overheating	O
;	O
extensive	O
HVAC	O
systems	O
are	O
used	O
to	O
prevent	O
this	O
.	O
</s>
<s>
Solutions	O
to	O
reduce	O
heat	O
include	O
using	O
lower	O
power-consumption	O
ARM	B-Architecture
or	O
Intel	B-Device
Atom	I-Device
processors	O
.	O
</s>
<s>
Mobile	O
devices	O
usually	O
have	O
no	O
discrete	O
cooling	O
systems	O
,	O
as	O
mobile	O
CPU	B-General_Concept
and	O
GPU	B-Architecture
chips	O
are	O
designed	O
for	O
maximum	O
power	O
efficiency	O
due	O
to	O
the	O
constraints	O
of	O
the	O
device	O
's	O
battery	O
.	O
</s>
