<s>
Underclocking	B-Device
,	O
also	O
known	O
as	O
downclocking	B-Device
,	O
is	O
modifying	O
a	O
computer	O
or	O
electronic	O
circuit	O
's	O
timing	O
settings	O
to	O
run	O
at	O
a	O
lower	O
clock	O
rate	O
than	O
is	O
specified	O
.	O
</s>
<s>
Underclocking	B-Device
is	O
used	O
to	O
reduce	O
a	O
computer	O
's	O
power	B-General_Concept
consumption	I-General_Concept
,	O
increase	O
battery	O
life	O
,	O
reduce	O
heat	O
emission	O
,	O
and	O
it	O
may	O
also	O
increase	O
the	O
system	O
's	O
stability	O
,	O
lifespan/reliability	O
and	O
compatibility	B-Device
.	O
</s>
<s>
Underclocking	B-Device
may	O
be	O
implemented	O
by	O
the	O
factory	O
,	O
but	O
many	O
computers	O
and	O
components	O
may	O
be	O
underclocked	B-Device
by	O
the	O
end	O
user	O
.	O
</s>
<s>
For	O
microprocessors	O
,	O
the	O
purpose	O
is	O
generally	O
to	O
decrease	O
the	O
need	O
for	O
heat	B-General_Concept
dissipation	I-General_Concept
devices	I-General_Concept
or	O
decrease	O
the	O
electrical	O
power	B-General_Concept
consumption	I-General_Concept
.	O
</s>
<s>
For	O
example	O
,	O
a	O
Pentium	O
4	O
processor	O
normally	O
clocked	O
at	O
3.4GHz	O
can	O
be	O
"	O
underclocked	B-Device
"	O
to	O
2GHz	O
and	O
can	O
then	O
be	O
safely	O
run	O
with	O
reduced	O
fan	O
speeds	O
.	O
</s>
<s>
However	O
,	O
the	O
proportional	O
performance	O
reduction	O
is	O
usually	O
less	O
than	O
the	O
proportional	O
reduction	O
in	O
clock	O
speed	O
because	O
performance	O
is	O
often	O
limited	O
by	O
other	O
bottlenecks	O
:	O
the	O
hard	B-Device
disk	I-Device
,	O
GPU	B-Architecture
,	O
disk	B-General_Concept
controller	I-General_Concept
,	O
Internet	O
,	O
network	B-Architecture
,	O
etc	O
.	O
</s>
<s>
Underclocking	B-Device
refers	O
to	O
alterations	O
of	O
the	O
timing	O
of	O
a	O
synchronous	O
circuit	O
in	O
order	O
to	O
lower	O
a	O
device	O
's	O
energy	O
needs	O
.	O
</s>
<s>
Deliberate	O
underclocking	B-Device
involves	O
limiting	O
a	O
processor	O
's	O
speed	O
,	O
which	O
may	O
affect	O
the	O
speed	O
of	O
operations	O
,	O
but	O
may	O
or	O
may	O
not	O
make	O
a	O
device	O
noticeably	O
less	O
able	O
,	O
depending	O
on	O
other	O
hardware	O
and	O
desired	O
use	O
.	O
</s>
<s>
Many	O
computers	O
and	O
other	O
devices	O
allow	O
for	O
underclocking	B-Device
.	O
</s>
<s>
Manufacturers	O
add	O
underclocking	B-Device
options	O
for	O
many	O
reasons	O
.	O
</s>
<s>
Underclocking	B-Device
can	O
help	O
with	O
excessive	O
heat	O
buildup	O
,	O
because	O
lower	O
performance	O
will	O
not	O
generate	O
as	O
much	O
heat	O
inside	O
the	O
device	O
.	O
</s>
<s>
Laptop	O
computers	O
and	O
other	O
battery-operated	O
devices	O
often	O
have	O
underclocking	B-Device
settings	O
,	O
so	O
that	O
batteries	O
can	O
last	O
longer	O
without	O
being	O
charged	O
.	O
</s>
<s>
In	O
addition	O
to	O
providing	O
underclocking	B-Device
features	O
,	O
manufacturers	O
can	O
choose	O
to	O
limit	O
the	O
capability	O
of	O
a	O
machine	O
in	O
order	O
to	O
make	O
it	O
more	O
efficient	O
.	O
</s>
<s>
Underclocking	B-Device
can	O
also	O
be	O
performed	O
on	O
graphics	B-Device
card	I-Device
processor	O
's	O
GPUs	B-Architecture
,	O
usually	O
with	O
the	O
aim	O
of	O
reducing	O
heat	O
output	O
.	O
</s>
<s>
For	O
instance	O
,	O
it	O
is	O
possible	O
to	O
set	O
a	O
GPU	B-Architecture
to	O
run	O
at	O
lower	O
clock	O
rates	O
when	O
performing	O
everyday	O
tasks	O
(	O
e.g.	O
</s>
<s>
The	O
GPU	B-Architecture
can	O
then	O
be	O
overclocked	O
for	O
more	O
graphically	O
intense	O
applications	O
,	O
such	O
as	O
games	O
.	O
</s>
<s>
Underclocking	B-Device
a	O
GPU	B-Architecture
will	O
reduce	O
performance	O
,	O
but	O
this	O
decrease	O
will	O
probably	O
not	O
be	O
noticeable	O
except	O
in	O
graphically	O
intensive	O
applications	O
.	O
</s>
<s>
Newer	O
and	O
faster	O
RAM	B-Architecture
may	O
be	O
underclocked	B-Device
to	O
match	O
older	O
systems	O
as	O
an	O
inexpensive	O
way	O
to	O
replace	O
rare	O
or	O
discontinued	O
memory	O
.	O
</s>
<s>
If	O
a	O
PC	O
processor	O
is	O
underclocked	B-Device
,	O
and	O
the	O
clock	O
factor	O
or	O
multiplier	O
(	O
the	O
ratio	O
between	O
the	O
processor	O
and	O
the	O
memory	O
clock	O
speed	O
)	O
is	O
unchanged	O
,	O
the	O
memory	O
will	O
also	O
be	O
underclocked	B-Device
.	O
</s>
<s>
Dynamic	B-General_Concept
frequency	I-General_Concept
scaling	I-General_Concept
(	O
automatic	O
underclocking	B-Device
)	O
is	O
very	O
common	O
on	O
laptop	O
computers	O
and	O
has	O
become	O
common	O
on	O
desktop	O
computers	O
as	O
well	O
.	O
</s>
<s>
In	O
laptops	O
,	O
the	O
processor	O
is	O
usually	O
underclocked	B-Device
automatically	O
whenever	O
the	O
computer	O
is	O
operating	O
on	O
batteries	O
.	O
</s>
<s>
Most	O
modern	O
notebook	O
and	O
desktop	O
processors	O
(	O
utilizing	O
power-saving	O
schemes	O
like	O
AMD	O
's	O
Cool'n'Quiet	B-Device
and	O
PowerNow	B-Device
!	I-Device
)	O
</s>
<s>
will	O
underclock	B-Device
themselves	O
automatically	O
under	O
a	O
light	O
processing	O
load	O
,	O
when	O
the	O
machine	O
BIOS	B-Operating_System
and	O
the	O
operating	O
system	O
support	O
it	O
.	O
</s>
<s>
Intel	O
has	O
also	O
used	O
this	O
method	O
on	O
numerous	O
processors	O
through	O
a	O
feature	O
called	O
SpeedStep	B-Device
.	O
</s>
<s>
SpeedStep	B-Device
first	O
appeared	O
on	O
chips	O
like	O
the	O
Core	O
2	O
Duo	O
and	O
selective	O
Pentium	O
models	O
,	O
later	O
becoming	O
a	O
standard	O
in	O
mid	O
to	O
high-end	O
Core	O
i3	O
,	O
i5	O
,	O
and	O
i7	O
models	O
.	O
</s>
<s>
Some	O
processors	O
underclock	B-Device
automatically	O
as	O
a	O
defensive	O
measure	O
,	O
to	O
prevent	O
overheating	O
which	O
could	O
cause	O
permanent	O
damage	O
.	O
</s>
<s>
When	O
such	O
a	O
processor	O
reaches	O
a	O
temperature	O
level	O
deemed	O
too	O
high	O
for	O
safe	O
operation	O
,	O
the	O
thermal	O
control	O
circuit	O
activates	O
,	O
automatically	O
decreasing	O
the	O
clock	O
and	O
CPU	B-Device
core	I-Device
voltage	I-Device
until	O
the	O
temperature	O
has	O
returned	O
to	O
a	O
safe	O
level	O
.	O
</s>
<s>
There	O
are	O
several	O
different	O
underclocking	B-Device
competitions	O
similar	O
in	O
format	O
to	O
overclocking	B-Application
competitions	O
,	O
except	O
the	O
goal	O
is	O
to	O
have	O
the	O
lowest	O
clocked	O
computer	O
,	O
as	O
opposed	O
to	O
the	O
highest	O
.	O
</s>
<s>
Reduced	O
electrical	O
power	B-General_Concept
consumption	I-General_Concept
,	O
especially	O
when	O
combined	O
with	O
undervolting	O
(	O
i.e.	O
,	O
reducing	O
the	O
component	O
's	O
voltage	O
below	O
the	O
nominal	O
)	O
.	O
</s>
<s>
For	O
instance	O
,	O
by	O
underclocking	B-Device
an	O
Athlon	O
XP	O
1700+	O
processor	O
from	O
1466	O
to	O
1000MHz	O
and	O
reducing	O
the	O
core	B-Device
voltage	I-Device
from	O
1.75	O
to	O
1.15V	O
,	O
a	O
computer	O
user	O
reduced	O
the	O
power	B-General_Concept
consumption	I-General_Concept
from	O
64.0	O
to	O
21.6W	O
,	O
i.e.	O
,	O
66%	O
power	O
reduction	O
,	O
with	O
only	O
26%	O
less	O
performance	O
.	O
</s>
<s>
The	O
same	O
is	O
true	O
for	O
newer	O
processors	O
:	O
When	O
a	O
single-core	O
Intel	O
CPU	O
was	O
20%	O
underclocked	B-Device
,	O
the	O
PC	O
's	O
performance	O
was	O
down	O
only	O
13%	O
with	O
a	O
49%	O
power	O
reduction	O
.	O
</s>
<s>
Reduced	O
heat	O
generation	O
,	O
which	O
is	O
exactly	O
proportional	O
to	O
the	O
power	B-General_Concept
consumption	I-General_Concept
.	O
</s>
<s>
Better	O
compatibility	B-Device
with	O
old	O
applications	O
.	O
</s>
<s>
Linux	B-Operating_System
kernel	I-Operating_System
supports	O
CPU	O
frequency	O
modulation	O
.	O
</s>
<s>
The	O
kernel	B-Operating_System
includes	O
five	O
governors	O
by	O
default	O
:	O
Conservative	O
,	O
Ondemand	O
,	O
Performance	O
,	O
Powersave	O
,	O
and	O
Userspace	O
.	O
</s>
<s>
Underclocking	B-Device
can	O
be	O
done	O
manually	O
in	O
the	O
BIOS	B-Operating_System
or	O
with	O
Windows	B-Application
applications	I-Application
,	O
or	O
dynamically	O
using	O
features	O
such	O
as	O
Intel	O
's	O
SpeedStep	B-Device
or	O
AMD	O
's	O
Cool'n'Quiet	B-Device
.	O
</s>
<s>
In	O
Windows	B-Application
7	O
and	O
10	O
,	O
underclocking	B-Device
can	O
be	O
set	O
within	O
the	O
"	O
advanced	O
"	O
settings	O
of	O
a	O
power	O
management	O
plan	O
.	O
</s>
<s>
Earlier	O
models	O
of	O
the	O
Asus	B-Device
Eee	I-Device
PC	I-Device
used	O
a	O
900MHz	O
Intel	B-Device
Celeron	I-Device
M	O
processor	O
underclocked	B-Device
to	O
630MHz	O
.	O
</s>
<s>
Underclocking	B-Device
can	O
be	O
performed	O
in	O
the	O
EFI	O
.	O
</s>
<s>
Most	O
smartphones	B-Application
and	O
PDAs	B-Application
,	O
such	O
as	O
the	O
Motorola	B-Application
Droid	I-Application
,	O
Palm	B-Application
Pre	I-Application
,	O
and	O
Apple	O
iPhone	B-Device
,	O
use	O
underclocking	B-Device
of	O
a	O
more	O
powerful	O
processor	O
,	O
rather	O
than	O
the	O
full	O
clocking	O
of	O
a	O
less	O
powerful	O
processor	O
,	O
to	O
maximize	O
battery	O
life	O
.	O
</s>
<s>
The	O
performance	O
of	O
an	O
underclocked	B-Device
machine	O
will	O
often	O
be	O
better	O
than	O
might	O
be	O
expected	O
.	O
</s>
<s>
Such	O
devices	O
communicate	O
with	O
the	O
CPU	O
through	O
a	O
bus	B-General_Concept
which	O
operates	O
at	O
a	O
much	O
lower	O
bandwidth	O
.	O
</s>
<s>
Generally	O
,	O
the	O
lower	O
the	O
CPU	O
multiplier	O
(	O
and	O
thus	O
clockrate	O
of	O
a	O
CPU	O
)	O
,	O
the	O
closer	O
its	O
performance	O
will	O
be	O
to	O
that	O
of	O
the	O
bus	B-General_Concept
,	O
and	O
the	O
less	O
time	O
it	O
will	O
spend	O
waiting	O
.	O
</s>
