<s>
Advanced	B-Device
Configuration	I-Device
and	I-Device
Power	I-Device
Interface	I-Device
(	O
ACPI	B-Device
)	O
is	O
an	O
open	O
standard	O
that	O
operating	B-General_Concept
systems	I-General_Concept
can	O
use	O
to	O
discover	O
and	O
configure	O
computer	B-Architecture
hardware	I-Architecture
components	O
,	O
to	O
perform	O
power	O
management	O
(	O
e.g.	O
</s>
<s>
putting	O
unused	O
hardware	B-Architecture
components	O
to	O
sleep	O
)	O
,	O
auto	O
configuration	O
(	O
e.g.	O
</s>
<s>
Plug	B-Device
and	I-Device
Play	I-Device
and	O
hot	B-Device
swapping	I-Device
)	O
,	O
and	O
status	O
monitoring	O
.	O
</s>
<s>
First	O
released	O
in	O
December	O
1996	O
,	O
ACPI	B-Device
aims	O
to	O
replace	O
Advanced	B-Device
Power	I-Device
Management	I-Device
(	O
APM	O
)	O
,	O
the	O
MultiProcessor	B-Device
Specification	I-Device
,	O
and	O
the	O
Plug	B-Device
and	I-Device
Play	I-Device
BIOS	I-Device
(	O
PnP	O
)	O
Specification	O
.	O
</s>
<s>
ACPI	B-Device
brings	O
power	O
management	O
under	O
the	O
control	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
as	O
opposed	O
to	O
the	O
previous	O
BIOS-centric	O
system	O
that	O
relied	O
on	O
platform-specific	O
firmware	B-Application
to	O
determine	O
power	O
management	O
and	O
configuration	O
policies	O
.	O
</s>
<s>
The	O
specification	O
is	O
central	O
to	O
the	O
Operating	B-Device
System-directed	I-Device
configuration	I-Device
and	I-Device
Power	I-Device
Management	I-Device
(	O
OSPM	O
)	O
system	O
.	O
</s>
<s>
ACPI	B-Device
defines	O
hardware	B-Operating_System
abstraction	I-Operating_System
interfaces	O
between	O
the	O
device	O
's	O
firmware	B-Application
(	O
e.g.	O
</s>
<s>
BIOS	B-Operating_System
,	O
UEFI	B-Architecture
)	O
,	O
the	O
computer	B-Architecture
hardware	I-Architecture
components	O
,	O
and	O
the	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Internally	O
,	O
ACPI	B-Device
advertises	O
the	O
available	O
components	O
and	O
their	O
functions	O
to	O
the	O
operating	B-Operating_System
system	I-Operating_System
kernel	I-Operating_System
using	O
instruction	O
lists	O
(	O
"	O
methods	B-Language
"	O
)	O
provided	O
through	O
the	O
system	O
firmware	B-Application
(	O
UEFI	B-Architecture
or	O
BIOS	B-Operating_System
)	O
,	O
which	O
the	O
kernel	B-Operating_System
parses	O
.	O
</s>
<s>
ACPI	B-Device
then	O
executes	O
the	O
desired	O
operations	O
written	O
in	O
ACPI	B-Device
Machine	O
Language	O
(	O
such	O
as	O
the	O
initialization	O
of	O
hardware	B-Architecture
components	O
)	O
using	O
an	O
embedded	O
minimal	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
In	O
October	O
2013	O
,	O
ACPI	B-Device
Special	O
Interest	O
Group	O
(	O
ACPI	B-Device
SIG	O
)	O
,	O
the	O
original	O
developers	O
of	O
the	O
ACPI	B-Device
standard	O
,	O
agreed	O
to	O
transfer	O
all	O
assets	O
to	O
the	O
UEFI	B-Device
Forum	I-Device
,	O
in	O
which	O
all	O
future	O
development	O
will	O
take	O
place	O
.	O
</s>
<s>
The	O
UEFI	B-Device
Forum	I-Device
published	O
of	O
the	O
standard	O
,	O
"	O
Release	O
6.5	O
"	O
in	O
August	O
2022	O
.	O
</s>
<s>
The	O
firmware-level	O
ACPI	B-Device
has	O
three	O
main	O
components	O
:	O
the	O
ACPI	B-Device
tables	O
,	O
the	O
ACPI	B-Device
BIOS	B-Operating_System
,	O
and	O
the	O
ACPI	B-Device
registers	O
.	O
</s>
<s>
The	O
ACPI	B-Device
BIOS	B-Operating_System
generates	O
ACPI	B-Device
tables	O
and	O
loads	O
ACPI	B-Device
tables	O
into	O
main	B-Architecture
memory	I-Architecture
.	O
</s>
<s>
Much	O
of	O
the	O
firmware	B-Application
ACPI	B-Device
functionality	O
is	O
provided	O
in	O
bytecode	O
of	O
ACPI	B-Device
Machine	O
Language	O
(	O
AML	O
)	O
,	O
a	O
Turing-complete	O
,	O
domain-specific	B-Language
low-level	B-Language
language	I-Language
,	O
stored	O
in	O
the	O
ACPI	B-Device
tables	O
.	O
</s>
<s>
To	O
make	O
use	O
of	O
the	O
ACPI	B-Device
tables	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
must	O
have	O
an	O
interpreter	B-Application
for	O
the	O
AML	O
bytecode	O
.	O
</s>
<s>
A	O
reference	O
AML	O
interpreter	B-Application
implementation	O
is	O
provided	O
by	O
the	O
ACPI	B-Device
Component	O
Architecture	O
(	O
ACPICA	O
)	O
.	O
</s>
<s>
At	O
the	O
BIOS	B-Operating_System
development	O
time	O
,	O
AML	O
bytecode	O
is	O
compiled	O
from	O
the	O
ASL	O
(	O
ACPI	B-Device
Source	O
Language	O
)	O
code	O
.	O
</s>
<s>
In	O
November	O
2003	O
,	O
Linus	O
Torvalds	O
—	O
author	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
—	O
described	O
ACPI	B-Device
as	O
"	O
a	O
complete	O
design	O
disaster	O
in	O
every	O
way	O
"	O
.	O
</s>
<s>
In	O
2014	O
,	O
Mark	O
Shuttleworth	O
,	O
founder	O
of	O
the	O
Ubuntu	B-Operating_System
Linux	I-Operating_System
distribution	I-Operating_System
,	O
compared	O
ACPI	B-Device
with	O
Trojan	O
horses	O
.	O
</s>
<s>
The	O
ACPI	B-Device
Component	O
Architecture	O
(	O
ACPICA	O
)	O
,	O
mainly	O
written	O
by	O
Intel	O
's	O
engineers	O
,	O
provides	O
an	O
open-source	O
platform-independent	O
reference	O
implementation	O
of	O
the	O
operating	O
systemrelated	O
ACPI	B-Device
code	O
.	O
</s>
<s>
The	O
ACPICA	O
code	O
is	O
used	O
by	O
Linux	B-Application
,	O
Haiku	B-Language
,	O
ArcaOS	B-Device
and	O
FreeBSD	B-Operating_System
,	O
which	O
supplement	O
it	O
with	O
their	O
operating-system	O
specific	O
code	O
.	O
</s>
<s>
The	O
first	O
revision	O
of	O
the	O
ACPI	B-Device
specification	O
was	O
released	O
in	O
December	O
1996	O
,	O
supporting	O
16	O
,	O
24	O
and	O
32-bit	O
addressing	O
spaces	O
.	O
</s>
<s>
It	O
was	O
not	O
until	O
August	O
2000	O
that	O
ACPI	B-Device
received	O
64-bit	B-Device
address	O
support	O
as	O
well	O
as	O
support	O
for	O
multiprocessor	B-Operating_System
workstations	O
and	O
servers	O
with	O
revision	O
2.0	O
.	O
</s>
<s>
In	O
1999	O
,	O
then	O
Microsoft	O
CEO	O
Bill	O
Gates	O
stated	O
in	O
an	O
e-mail	O
that	O
Linux	B-Application
would	O
benefit	O
from	O
ACPI	B-Device
without	O
them	O
having	O
to	O
do	O
work	O
and	O
suggested	O
to	O
make	O
it	O
Windows-only	O
.	O
</s>
<s>
In	O
September	O
2004	O
,	O
revision	O
3.0	O
was	O
released	O
,	O
bringing	O
to	O
the	O
ACPI	B-Device
specification	O
support	O
for	O
SATA	O
interfaces	O
,	O
PCI	O
Express	O
bus	O
,	O
multiprocessor	B-Operating_System
support	O
for	O
more	O
than	O
256	O
processors	O
,	O
ambient	O
light	O
sensors	O
and	O
user-presence	O
devices	O
,	O
as	O
well	O
as	O
extending	O
the	O
thermal	O
model	O
beyond	O
the	O
previous	O
processor-centric	O
support	O
.	O
</s>
<s>
Released	O
in	O
June	O
2009	O
,	O
revision	O
4.0	O
of	O
the	O
ACPI	B-Device
specification	O
added	O
various	O
new	O
features	O
to	O
the	O
design	O
;	O
most	O
notable	O
are	O
the	O
USB	B-Protocol
3.0	O
support	O
,	O
logical	O
processor	O
idling	O
support	O
,	O
and	O
x2APIC	O
support	O
.	O
</s>
<s>
Revision	O
5.0	O
of	O
the	O
ACPI	B-Device
specification	O
was	O
released	O
in	O
December	O
2011	O
,	O
which	O
added	O
the	O
ARM	B-Architecture
architecture	I-Architecture
support	O
.	O
</s>
<s>
Microsoft	O
's	O
Windows	B-Device
98	I-Device
was	O
the	O
first	O
operating	B-General_Concept
system	I-General_Concept
to	O
implement	O
ACPI	B-Device
,	O
but	O
its	O
implementation	O
was	O
somewhat	O
buggy	O
or	O
incomplete	O
,	O
although	O
some	O
of	O
the	O
problems	O
associated	O
with	O
it	O
were	O
caused	O
by	O
the	O
first-generation	O
ACPI	B-Device
hardware	B-Architecture
.	O
</s>
<s>
Other	O
operating	B-General_Concept
systems	I-General_Concept
,	O
including	O
later	O
versions	O
of	O
Windows	O
,	O
macOS	B-Application
,	O
eComStation	B-Device
,	O
ArcaOS	B-Device
,	O
FreeBSD	B-Operating_System
(	O
since	O
FreeBSD	B-Operating_System
5.0	O
)	O
,	O
NetBSD	B-Device
(	O
since	O
NetBSD	B-Device
1.6	O
)	O
,	O
OpenBSD	B-Operating_System
(	O
since	O
OpenBSD	B-Operating_System
3.8	O
)	O
,	O
HP-UX	B-Application
,	O
OpenVMS	B-Operating_System
,	O
Linux	B-Application
,	O
GNU	B-Application
Hurd	I-Application
and	O
PC	O
versions	O
of	O
Solaris	B-Application
,	O
have	O
at	O
least	O
some	O
support	O
for	O
ACPI	B-Device
.	O
</s>
<s>
Some	O
newer	O
operating	B-General_Concept
systems	I-General_Concept
,	O
like	O
Windows	B-Application
Vista	I-Application
,	O
require	O
the	O
computer	O
to	O
have	O
an	O
ACPI-compliant	O
BIOS	B-Operating_System
,	O
and	O
since	O
Windows	B-Application
8	I-Application
,	O
the	O
S0ix/Modern	B-Device
Standby	I-Device
state	O
was	O
implemented	O
.	O
</s>
<s>
Windows	O
operating	B-General_Concept
systems	I-General_Concept
use	O
acpi.sys	O
to	O
access	O
ACPI	B-Device
events	O
.	O
</s>
<s>
The	O
2.4	O
series	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
had	O
only	O
minimal	O
support	O
for	O
ACPI	B-Device
,	O
with	O
better	O
support	O
implemented	O
(	O
and	O
enabled	O
by	O
default	O
)	O
from	O
kernel	B-Operating_System
version	O
2.6.0	O
onwards	O
.	O
</s>
<s>
Old	O
ACPI	B-Device
BIOS	B-Operating_System
implementations	O
tend	O
to	O
be	O
quite	O
buggy	O
,	O
and	O
consequently	O
are	O
not	O
supported	O
by	O
later	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
For	O
example	O
,	O
Windows	B-Application
2000	I-Application
,	O
Windows	B-Application
XP	I-Application
,	O
and	O
Windows	B-Application
Server	I-Application
2003	I-Application
only	O
use	O
ACPI	B-Device
if	O
the	O
BIOS	B-Operating_System
date	O
is	O
after	O
January	O
1	O
,	O
1999	O
.	O
</s>
<s>
Similarly	O
,	O
Linux	B-Operating_System
kernel	I-Operating_System
2.6	I-Operating_System
blacklisted	O
any	O
ACPI	B-Device
BIOS	B-Operating_System
from	O
before	O
January	O
1	O
,	O
2001	O
.	O
</s>
<s>
Linux-based	B-Application
operating	I-Application
systems	I-Application
can	O
provide	O
handling	O
of	O
ACPI	B-Device
events	O
via	O
acpid	O
.	O
</s>
<s>
Once	O
an	O
OSPM-compatible	O
operating	B-General_Concept
system	I-General_Concept
activates	O
ACPI	B-Device
,	O
it	O
takes	O
exclusive	O
control	O
of	O
all	O
aspects	O
of	O
power	O
management	O
and	O
device	O
configuration	O
.	O
</s>
<s>
The	O
OSPM	O
implementation	O
must	O
expose	O
an	O
ACPI-compatible	O
environment	O
to	O
device	O
drivers	O
,	O
which	O
exposes	O
certain	O
system	O
,	O
device	O
and	O
processor	O
states	O
.	O
</s>
<s>
The	O
ACPI	B-Device
Specification	O
defines	O
the	O
following	O
four	O
global	O
"	O
Gx	O
"	O
states	O
and	O
six	O
sleep	O
"	O
Sx	O
"	O
states	O
for	O
an	O
ACPI-compliant	O
computer	O
system	O
:	O
</s>
<s>
The	O
power	O
to	O
the	O
CPU(s )	O
and	O
RAM	B-Architecture
is	O
maintained	O
.	O
</s>
<s>
Dirty	O
cache	O
is	O
flushed	O
to	O
RAM.S3commonly	O
referred	O
to	O
as	O
Standby	O
,	O
Sleep	O
,	O
or	O
Suspend	O
to	O
RAM	B-Architecture
(	O
STR	O
)	O
:	O
RAM	B-Architecture
remains	O
powered.S4Hibernation	O
or	O
Suspend	O
to	O
Disk	O
:	O
All	O
content	O
of	O
the	O
main	B-Architecture
memory	I-Architecture
is	O
saved	O
to	O
non-volatile	B-General_Concept
memory	I-General_Concept
such	O
as	O
a	O
hard	B-Device
drive	I-Device
,	O
and	O
the	O
system	O
is	O
powered	O
down.G2Soft	O
OffS5G2/S5	O
is	O
almost	O
the	O
same	O
as	O
G3	O
Mechanical	O
Off	O
,	O
except	O
that	O
the	O
power	O
supply	O
unit	O
(	O
PSU	O
)	O
still	O
supplies	O
power	O
,	O
at	O
a	O
minimum	O
,	O
to	O
the	O
power	O
button	O
to	O
allow	O
return	O
to	O
S0	O
.	O
</s>
<s>
Other	O
components	O
may	O
remain	O
powered	O
so	O
the	O
computer	O
can	O
"	O
wake	O
"	O
on	O
input	O
from	O
the	O
keyboard	O
,	O
clock	O
,	O
modem	B-Device
,	O
LAN	B-Protocol
,	O
or	O
USB	O
device.G3Mechanical	O
OffThe	O
computer	O
's	O
power	O
has	O
been	O
totally	O
removed	O
via	O
a	O
mechanical	O
switch	O
(	O
as	O
on	O
the	O
rear	O
of	O
a	O
PSU	O
)	O
.	O
</s>
<s>
The	O
specification	O
also	O
defines	O
a	O
Legacy	O
state	O
:	O
the	O
state	O
of	O
an	O
operating	B-General_Concept
system	I-General_Concept
which	O
does	O
not	O
support	O
ACPI	B-Device
.	O
</s>
<s>
In	O
this	O
state	O
,	O
the	O
hardware	B-Architecture
and	O
power	O
are	O
not	O
managed	O
via	O
ACPI	B-Device
,	O
effectively	O
disabling	O
ACPI	B-Device
.	O
</s>
<s>
All	O
ACPI-conformant	O
processors	O
must	O
support	O
this	O
power	O
state	O
.	O
</s>
<s>
Some	O
processors	O
,	O
such	O
as	O
the	O
Pentium	B-General_Concept
4	I-General_Concept
and	O
AMD	B-Architecture
Athlon	I-Architecture
,	O
also	O
support	O
an	O
Enhanced	O
C1	O
state	O
(	O
C1E	O
or	O
Enhanced	O
Halt	O
State	O
)	O
for	O
lower	O
power	O
consumption	O
,	O
however	O
this	O
proved	O
to	O
be	O
buggy	O
on	O
some	O
systems	O
.	O
</s>
<s>
C3	O
(	O
often	O
known	O
as	O
Sleep	O
)	O
is	O
a	O
state	O
where	O
the	O
processor	O
does	O
not	O
need	O
to	O
keep	O
its	O
cache	B-General_Concept
coherent	I-General_Concept
,	O
but	O
maintains	O
other	O
state	O
.	O
</s>
<s>
For	O
example	O
,	O
Intel	O
's	O
Haswell	B-Device
platform	O
has	O
states	O
up	O
to	O
C10	O
,	O
where	O
it	O
distinguishes	O
core	O
states	O
and	O
package	O
states	O
.	O
</s>
<s>
P-states	O
have	O
become	O
known	O
as	O
SpeedStep	B-Device
in	O
Intel	O
processors	O
,	O
as	O
PowerNow	B-Device
!	I-Device
</s>
<s>
or	O
Cool'n'Quiet	B-Device
in	O
AMD	O
processors	O
,	O
and	O
as	O
PowerSaver	B-Device
in	O
VIA	O
processors	O
.	O
</s>
<s>
ACPI-compliant	O
systems	O
interact	O
with	O
hardware	B-Architecture
through	O
either	O
a	O
"	O
Function	O
Fixed	O
Hardware	B-Architecture
(	O
FFH	O
)	O
Interface	O
"	O
,	O
or	O
a	O
platform-independent	O
hardware	B-Architecture
programming	O
model	O
which	O
relies	O
on	O
platform-specific	O
ACPI	B-Device
Machine	O
Language	O
(	O
AML	O
)	O
provided	O
by	O
the	O
original	O
equipment	O
manufacturer	O
(	O
OEM	O
)	O
.	O
</s>
<s>
Function	O
Fixed	O
Hardware	B-Architecture
interfaces	O
are	O
platform-specific	O
features	O
,	O
provided	O
by	O
platform	O
manufacturers	O
for	O
the	O
purposes	O
of	O
performance	O
and	O
failure	O
recovery	O
.	O
</s>
<s>
Standard	O
Intel-based	O
PCs	O
have	O
a	O
fixed	O
function	O
interface	O
defined	O
by	O
Intel	O
,	O
which	O
provides	O
a	O
set	O
of	O
core	O
functionality	O
that	O
reduces	O
an	O
ACPI-compliant	O
system	O
's	O
need	O
for	O
full	O
driver	O
stacks	O
for	O
providing	O
basic	O
functionality	O
during	O
boot	O
time	O
or	O
in	O
the	O
case	O
of	O
major	O
system	O
failure	O
.	O
</s>
<s>
ACPI	B-Device
Platform	O
Error	O
Interface	O
(	O
APEI	O
)	O
is	O
a	O
specification	O
for	O
reporting	O
of	O
hardware	B-Architecture
errors	O
,	O
e.g.	O
</s>
<s>
chipset	O
,	O
RAM	B-Architecture
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
ACPI	B-Device
defines	O
many	O
tables	O
that	O
provide	O
the	O
interface	O
between	O
an	O
ACPI-compliant	O
operating	B-General_Concept
system	I-General_Concept
and	O
system	O
firmware	B-Application
(	O
BIOS	B-Operating_System
or	O
UEFI	B-Architecture
)	O
.	O
</s>
<s>
The	O
tables	O
allow	O
description	O
of	O
system	O
hardware	B-Architecture
in	O
a	O
platform-independent	O
manner	O
,	O
and	O
are	O
presented	O
as	O
either	O
fixed-formatted	O
data	O
structures	O
or	O
in	O
AML	O
.	O
</s>
<s>
The	O
AML	O
can	O
be	O
decompiled	O
by	O
tools	O
like	O
Intel	O
's	O
iASL	O
(	O
open-source	B-License
,	O
part	O
of	O
ACPICA	O
)	O
for	O
purposes	O
like	O
patching	O
the	O
tables	O
for	O
expanding	O
OS	O
compatibility	O
.	O
</s>
<s>
A	O
custom	O
ACPI	B-Device
table	O
called	O
the	O
Windows	O
Platform	O
Binary	O
Table	O
(	O
WPBT	O
)	O
is	O
used	O
by	O
Microsoft	O
to	O
allow	O
vendors	O
to	O
add	O
software	O
into	O
the	O
Windows	O
OS	O
automatically	O
.	O
</s>
<s>
Samsung	B-Application
shipped	O
PCs	O
with	O
Windows	O
Update	O
disabled	O
.	O
</s>
<s>
Ubuntu	B-Operating_System
founder	O
Mark	O
Shuttleworth	O
says	O
ACPI	B-Device
is	O
a	O
security	O
risk	O
.	O
</s>
<s>
He	O
says	O
"	O
arguing	O
for	O
ACPI	B-Device
on	O
your	O
next-generation	O
device	O
is	O
arguing	O
for	O
a	O
trojan	O
horse	O
of	O
monumental	O
proportions	O
to	O
be	O
installed	O
in	O
your	O
living	O
room	O
and	O
in	O
your	O
data	O
centre	O
"	O
and	O
"	O
firmware	B-Application
on	O
your	O
device	O
is	O
the	O
NSA	O
's	O
best	O
friend	O
"	O
.	O
</s>
<s>
He	O
goes	O
on	O
to	O
say	O
,	O
"	O
Your	O
biggest	O
mistake	O
is	O
to	O
assume	O
that	O
the	O
NSA	O
is	O
the	O
only	O
institution	O
abusing	O
this	O
position	O
of	O
trust	O
–	O
in	O
fact	O
,	O
it	O
's	O
reasonable	O
to	O
assume	O
that	O
all	O
firmware	B-Application
is	O
a	O
cesspool	O
of	O
insecurity	O
,	O
courtesy	O
of	O
incompetence	O
of	O
the	O
highest	O
degree	O
from	O
manufacturers	O
,	O
and	O
competence	O
of	O
the	O
highest	O
degree	O
from	O
a	O
very	O
wide	O
range	O
of	O
such	O
agencies.	O
"	O
</s>
<s>
He	O
suggests	O
open-source	B-License
,	O
declarative	B-Language
firmware	B-Application
(	O
ACPI	B-Device
or	O
non-ACPI	O
)	O
as	O
a	O
solution	O
.	O
</s>
