<s>
On	O
IBM	B-Device
PC	I-Device
compatible	O
computers	O
,	O
the	O
turbo	B-Device
button	I-Device
selects	O
one	O
of	O
two	O
run	O
states	O
:	O
the	O
default	O
"	O
turbo	O
"	O
speed	O
or	O
a	O
reduced	O
speed	O
closer	O
to	O
the	O
Intel	B-General_Concept
8086	I-General_Concept
CPU	O
.	O
</s>
<s>
It	O
was	O
relatively	O
common	O
on	O
computers	O
using	O
the	O
Intel	B-General_Concept
80286	I-General_Concept
,	O
Intel	B-General_Concept
80386	I-General_Concept
and	O
Intel	B-General_Concept
80486	I-General_Concept
processors	O
,	O
from	O
the	O
mid	O
1980s	O
to	O
mid	O
1990s	O
.	O
</s>
<s>
With	O
the	O
introduction	O
of	O
CPUs	O
which	O
ran	O
faster	O
than	O
the	O
original	O
4.77MHz	O
Intel	B-Device
8088	I-Device
used	O
in	O
the	O
IBM	B-Device
Personal	I-Device
Computer	I-Device
,	O
programs	O
which	O
relied	O
on	O
the	O
CPU	O
's	O
frequency	O
for	O
timing	O
were	O
executing	O
faster	O
than	O
intended	O
.	O
</s>
<s>
Disengaging	O
turbo	B-Device
mode	I-Device
slows	O
the	O
system	O
down	O
to	O
a	O
state	O
compatible	O
with	O
original	O
8086/8088	O
chips	O
.	O
</s>
<s>
On	O
most	O
systems	O
,	O
turbo	B-Device
mode	I-Device
was	O
with	O
the	O
button	O
pushed	O
in	O
,	O
but	O
since	O
the	O
button	O
could	O
often	O
be	O
wired	O
either	O
way	O
,	O
on	O
some	O
systems	O
it	O
was	O
the	O
opposite.The	O
turbo	B-Device
button	I-Device
could	O
be	O
linked	O
to	O
a	O
turbo	O
LED	O
or	O
two-digit	O
segmented	O
display	O
on	O
the	O
system	O
case	O
,	O
although	O
in	O
some	O
cases	O
,	O
the	O
indicated	O
frequency	O
(	O
in	O
MHz	O
)	O
was	O
not	O
a	O
measure	O
of	O
the	O
actual	O
processor	O
clocks	O
,	O
but	O
the	O
two	O
"	O
fast	O
"	O
and	O
"	O
slow	O
"	O
display	O
options	O
set	O
by	O
jumpers	B-Device
on	O
the	O
motherboard	B-Device
.	O
</s>
<s>
Some	O
systems	O
also	O
supported	O
keyboard	O
combinations	O
--	O
and	O
--	O
for	O
switching	O
turbo	B-Device
mode	I-Device
on	O
and	O
off	O
,	O
such	O
as	O
the	O
Packard	O
Bell	O
486ES	O
3x3	O
(	O
the	O
4x4	O
and	O
MT	O
models	O
had	O
a	O
dedicated	O
Turbo	B-Device
button	I-Device
)	O
.	O
</s>
<s>
With	O
all	O
the	O
486ES	O
models	O
—	O
those	O
with	O
and	O
without	O
a	O
turbo	B-Device
button	I-Device
—	O
the	O
power	O
light	O
would	O
show	O
green	O
in	O
normal	O
(	O
“	O
Turbo	O
”	O
)	O
mode	O
,	O
and	O
orange	O
in	O
Slow	O
mode	O
.	O
</s>
<s>
Some	O
keyboards	O
had	O
a	O
turbo	B-Device
button	I-Device
as	O
well	O
,	O
located	O
near	O
right	O
Shift	B-Device
.	O
</s>
<s>
Unlike	O
the	O
turbo	B-Device
button	I-Device
that	O
was	O
common	O
on	O
computer	O
cases	O
,	O
the	O
turbo	B-Device
button	I-Device
on	O
the	O
keyboards	O
did	O
not	O
control	O
the	O
clock	O
rate	O
of	O
the	O
CPU	O
;	O
rather	O
,	O
it	O
controlled	O
the	O
keyboard	O
repeat	O
rate	O
.	O
</s>
<s>
The	O
displayed	O
speed	O
can	O
vary	O
depending	O
on	O
the	O
CPU	O
's	O
frequency	O
,	O
and	O
the	O
settings	O
of	O
the	O
computer	O
,	O
however	O
,	O
it	O
is	O
not	O
measuring	O
the	O
frequency	O
of	O
the	O
CPU	O
,	O
it	O
displays	O
preset	O
numbers	O
when	O
turbo	O
is	O
turned	O
on	O
or	O
off	O
,	O
and	O
these	O
numbers	O
can	O
be	O
changed	O
with	O
two	O
(	O
or	O
three	O
)	O
banks	O
of	O
jumpers	B-Device
on	O
the	O
back	O
of	O
the	O
display	O
,	O
each	O
bank	O
changing	O
each	O
digit	O
,	O
as	O
their	O
purpose	O
is	O
to	O
connect	O
LED	O
's	O
in	O
the	O
display	O
to	O
(	O
or	O
disconnect	O
from	O
)	O
power	O
.	O
</s>
<s>
The	O
feature	O
was	O
relatively	O
common	O
on	O
systems	O
running	O
286	B-General_Concept
to	O
486	B-General_Concept
CPUs	O
,	O
</s>
<s>
and	O
less	O
common	O
on	O
Pentium	B-General_Concept
era	O
computers	O
.	O
</s>
<s>
While	O
the	O
implementation	O
of	O
an	O
actual	O
hardware	O
turbo	B-Device
button	I-Device
has	O
disappeared	O
on	O
modern	O
machines	O
,	O
software	O
developers	O
have	O
compensated	O
with	O
software	O
replacements	O
.	O
</s>
<s>
One	O
example	O
is	O
DOSBox	B-Application
,	O
which	O
offers	O
an	O
adjustable	O
emulation	O
rate	O
.	O
</s>
<s>
Modern	O
PCs	O
that	O
support	O
ACPI	B-Device
power	O
management	O
may	O
provide	O
software	O
controls	O
to	O
switch	O
ACPI	B-Device
performance	O
states	O
or	O
other	O
CPU	B-General_Concept
throttling	I-General_Concept
modes	O
.	O
</s>
<s>
Some	O
computers	O
have	O
wired	O
the	O
turbo	B-Device
button	I-Device
in	O
a	O
way	O
that	O
if	O
the	O
button	O
is	O
pressed	O
in	O
,	O
the	O
computer	O
is	O
running	O
in	O
the	O
slower	O
speed	O
.	O
</s>
<s>
While	O
the	O
turbo	B-Device
button	I-Device
can	O
be	O
configured	O
this	O
way	O
,	O
this	O
is	O
not	O
the	O
intended	O
way	O
of	O
using	O
the	O
button	O
,	O
as	O
the	O
computer	O
is	O
intended	O
to	O
run	O
at	O
full	O
speed	O
when	O
the	O
button	O
is	O
pressed	O
in	O
,	O
hence	O
the	O
name	O
turbo	O
.	O
</s>
<s>
This	O
issue	O
can	O
be	O
solved	O
by	O
reconnecting	O
the	O
wires	O
in	O
the	O
correct	O
way	O
on	O
either	O
the	O
display	O
,	O
or	O
on	O
the	O
motherboard	B-Device
of	O
the	O
computer	O
.	O
</s>
