<s>
Advanced	B-Device
power	I-Device
management	I-Device
(	O
APM	O
)	O
is	O
an	O
API	B-Application
developed	O
by	O
Intel	O
and	O
Microsoft	O
and	O
released	O
in	O
1992	O
which	O
enables	O
an	O
operating	B-General_Concept
system	I-General_Concept
running	O
an	O
IBM-compatible	O
personal	B-Device
computer	I-Device
to	O
work	O
with	O
the	O
BIOS	B-Operating_System
(	O
part	O
of	O
the	O
computer	O
's	O
firmware	B-Application
)	O
to	O
achieve	O
power	O
management	O
.	O
</s>
<s>
ACPI	B-Device
is	O
the	O
successor	O
to	O
APM	O
.	O
</s>
<s>
Microsoft	O
dropped	O
support	O
for	O
APM	O
in	O
Windows	B-Application
Vista	I-Application
.	O
</s>
<s>
The	O
Linux	B-Application
kernel	I-Application
still	O
mostly	O
supports	O
APM	O
,	O
though	O
support	O
for	O
APM	O
CPU	O
idle	O
was	O
dropped	O
in	O
version	O
3.0	O
.	O
</s>
<s>
This	O
driver	O
communicates	O
to	O
the	O
APM-aware	O
BIOS	B-Operating_System
,	O
which	O
controls	O
the	O
hardware	O
.	O
</s>
<s>
Communication	O
occurs	O
both	O
ways	O
;	O
power	O
management	O
events	O
are	O
sent	O
from	O
the	O
BIOS	B-Operating_System
to	O
the	O
APM	O
driver	O
,	O
and	O
the	O
APM	O
driver	O
sends	O
information	O
and	O
requests	O
to	O
the	O
BIOS	B-Operating_System
via	O
function	O
calls	O
.	O
</s>
<s>
In	O
this	O
way	O
the	O
APM	O
driver	O
is	O
an	O
intermediary	O
between	O
the	O
BIOS	B-Operating_System
and	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Power	O
management	O
happens	O
in	O
two	O
ways	O
;	O
through	O
the	O
above-mentioned	O
function	O
calls	O
from	O
the	O
APM	O
driver	O
to	O
the	O
BIOS	B-Operating_System
requesting	O
power	O
state	O
changes	O
,	O
and	O
automatically	O
based	O
on	O
device	O
activity	O
.	O
</s>
<s>
In	O
APM	O
1.0	O
and	O
APM	O
1.1	O
,	O
power	O
management	O
is	O
almost	O
fully	O
controlled	O
by	O
the	O
BIOS	B-Operating_System
.	O
</s>
<s>
In	O
APM	O
1.2	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
can	O
control	O
PM	O
time	O
(	O
e.g.	O
</s>
<s>
There	O
are	O
12	O
power	O
events	O
(	O
such	O
as	O
standby	O
,	O
suspend	O
and	O
resume	O
requests	O
,	O
and	O
low	O
battery	O
notifications	O
)	O
,	O
plus	O
OEM-defined	O
events	O
,	O
that	O
can	O
be	O
sent	O
from	O
the	O
APM	O
BIOS	B-Operating_System
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
APM	O
driver	O
regularly	O
polls	B-General_Concept
for	O
event	O
change	O
notifications	O
.	O
</s>
<s>
Example	O
function	O
calls	O
include	O
letting	O
the	O
BIOS	B-Operating_System
know	O
about	O
current	O
CPU	O
usage	O
(	O
the	O
BIOS	B-Operating_System
may	O
respond	O
to	O
such	O
a	O
call	O
by	O
placing	O
the	O
CPU	O
in	O
a	O
low-power	O
state	O
,	O
or	O
returning	O
it	O
to	O
its	O
full-power	O
state	O
)	O
,	O
retrieving	O
the	O
current	O
power	O
state	O
of	O
a	O
device	O
,	O
or	O
requesting	O
a	O
power	O
state	O
change	O
.	O
</s>
<s>
Enable/Disable	O
Power	O
Management	O
0x08	O
Restore	O
APM	O
BIOS	B-Operating_System
Power-On	O
Defaults	O
0x09	O
Get	O
Power	O
Status	O
0x0A	O
Supports	O
AC	O
status	O
"	O
On	O
backup	O
power	O
"	O
.	O
</s>
<s>
Get	O
Capabilities	O
0x10	O
Get/Set/Disable	O
Resume	O
Timer	O
0x11	O
Enable/Disable	O
Resume	O
on	O
Ring	O
Indicator	O
0x12	O
Enable/Disable	O
Timer	O
Based	O
Requests	O
0x13	O
OEM	O
APM	O
Installation	O
Check	O
0x80	O
Tells	O
if	O
APM	O
BIOS	B-Operating_System
supports	O
OEM	O
hardware	O
dependent	O
functions	O
.	O
</s>
<s>
The	O
CPU	O
core	O
(	O
defined	O
in	O
APM	O
as	O
the	O
CPU	O
clock	O
,	O
cache	B-General_Concept
,	O
system	B-Architecture
bus	I-Architecture
and	O
system	O
timers	O
)	O
is	O
treated	O
specially	O
in	O
APM	O
,	O
as	O
it	O
is	O
the	O
last	O
device	O
to	O
be	O
powered	O
down	O
,	O
and	O
the	O
first	O
device	O
to	O
be	O
powered	O
back	O
up	O
.	O
</s>
<s>
The	O
CPU	O
core	O
is	O
always	O
controlled	O
through	O
the	O
APM	O
BIOS	B-Operating_System
(	O
there	O
is	O
no	O
option	O
to	O
control	O
it	O
through	O
a	O
driver	O
)	O
.	O
</s>
<s>
Drivers	O
can	O
use	O
APM	O
function	O
calls	O
to	O
notify	O
the	O
BIOS	B-Operating_System
about	O
CPU	O
usage	O
,	O
but	O
it	O
is	O
up	O
to	O
the	O
BIOS	B-Operating_System
to	O
act	O
on	O
this	O
information	O
;	O
a	O
driver	O
cannot	O
directly	O
tell	O
the	O
CPU	O
to	O
go	O
into	O
a	O
power	O
saving	O
state	O
.	O
</s>
<s>
The	O
ATA	B-Protocol
specification	O
and	O
SATA	O
specification	O
defines	O
APM	O
provisions	O
for	O
hard	O
drives	O
,	O
which	O
specifies	O
a	O
trade-off	O
between	O
spin-down	O
frequency	O
and	O
always-on	O
performance	O
.	O
</s>
<s>
Unlike	O
the	O
BIOS-side	O
APM	O
,	O
the	O
ATA	B-Protocol
APM	O
and	O
SATA	O
APM	O
has	O
never	O
been	O
deprecated	O
.	O
</s>
