<s>
x86-64	B-Device
(	O
also	O
known	O
as	O
x64	B-Device
,	O
x86_64	O
,	O
AMD64	B-Device
,	O
and	O
Intel	O
64	O
)	O
is	O
a	O
64-bit	B-Application
version	O
of	O
the	O
x86	B-Operating_System
instruction	B-General_Concept
set	I-General_Concept
,	O
first	O
released	O
in	O
1999	O
.	O
</s>
<s>
It	O
introduced	O
two	O
new	O
modes	O
of	O
operation	O
,	O
64-bit	B-Application
mode	O
and	O
compatibility	O
mode	O
,	O
along	O
with	O
a	O
new	O
4-level	O
paging	B-Architecture
mode	O
.	O
</s>
<s>
With	O
64-bit	B-Application
mode	O
and	O
the	O
new	O
paging	B-Architecture
mode	O
,	O
it	O
supports	O
vastly	O
larger	O
amounts	O
of	O
virtual	B-Architecture
memory	I-Architecture
and	O
physical	O
memory	O
than	O
was	O
possible	O
on	O
its	O
32-bit	O
predecessors	O
,	O
allowing	O
programs	O
to	O
store	O
larger	O
amounts	O
of	O
data	O
in	O
memory	O
.	O
</s>
<s>
x86-64	B-Device
also	O
expands	O
general-purpose	B-General_Concept
registers	I-General_Concept
to	O
64-bit	B-Application
,	O
and	O
expands	O
the	O
number	O
of	O
them	O
from	O
8	O
(	O
some	O
of	O
which	O
had	O
limited	O
or	O
fixed	O
functionality	O
,	O
e.g.	O
</s>
<s>
for	O
stack	B-General_Concept
management	O
)	O
to	O
16	O
(	O
fully	O
general	O
)	O
,	O
and	O
provides	O
numerous	O
other	O
enhancements	O
.	O
</s>
<s>
Floating-point	B-Algorithm
arithmetic	I-Algorithm
is	O
supported	O
via	O
mandatory	O
SSE2-like	O
instructions	O
,	O
and	O
x87/MMX	O
style	O
registers	O
are	O
generally	O
not	O
used	O
(	O
but	O
still	O
available	O
even	O
in	O
64-bit	B-Application
mode	O
)	O
;	O
instead	O
,	O
a	O
set	O
of	O
16	O
vector	O
registers	O
,	O
128	O
bits	O
each	O
,	O
is	O
used	O
.	O
</s>
<s>
In	O
64-bit	B-Application
mode	O
,	O
instructions	O
are	O
modified	O
to	O
support	O
64-bit	B-Application
operands	O
and	O
64-bit	B-Application
addressing	B-Language
mode	I-Language
.	O
</s>
<s>
The	O
compatibility	O
mode	O
defined	O
in	O
the	O
architecture	O
allows	O
16	O
-	O
and	O
32-bit	O
user	B-Operating_System
applications	I-Operating_System
to	O
run	O
unmodified	O
,	O
coexisting	O
with	O
64-bit	B-Application
applications	O
if	O
the	O
64-bit	B-Application
operating	B-General_Concept
system	I-General_Concept
supports	O
them	O
.	O
</s>
<s>
As	O
the	O
full	O
x86	B-Operating_System
16-bit	O
and	O
32-bit	O
instruction	B-General_Concept
sets	I-General_Concept
remain	O
implemented	O
in	O
hardware	O
without	O
any	O
intervening	O
emulation	O
,	O
these	O
older	O
executables	B-Application
can	O
run	O
with	O
little	O
or	O
no	O
performance	O
penalty	O
,	O
</s>
<s>
Also	O
,	O
a	O
processor	O
supporting	O
x86-64	B-Device
still	O
powers	O
on	O
in	O
real	B-Application
mode	I-Application
for	O
full	O
backward	B-General_Concept
compatibility	I-General_Concept
with	O
the	O
8086	B-General_Concept
,	O
as	O
x86	B-Operating_System
processors	O
supporting	O
protected	B-Application
mode	I-Application
have	O
done	O
since	O
the	O
80286	B-General_Concept
.	O
</s>
<s>
The	O
AMD	B-Device
K8	I-Device
microarchitecture	B-General_Concept
,	O
in	O
the	O
Opteron	B-General_Concept
and	O
Athlon	O
64	O
processors	O
,	O
was	O
the	O
first	O
to	O
implement	O
it	O
.	O
</s>
<s>
This	O
was	O
the	O
first	O
significant	O
addition	O
to	O
the	O
x86	B-Operating_System
architecture	I-Operating_System
designed	O
by	O
a	O
company	O
other	O
than	O
Intel	O
.	O
</s>
<s>
Intel	O
was	O
forced	O
to	O
follow	O
suit	O
and	O
introduced	O
a	O
modified	O
NetBurst	B-Device
family	O
which	O
was	O
software-compatible	O
with	O
AMD	O
's	O
specification	O
.	O
</s>
<s>
VIA	O
Technologies	O
introduced	O
x86-64	B-Device
in	O
their	O
VIA	B-Device
Isaiah	I-Device
architecture	O
,	O
with	O
the	O
VIA	B-Device
Nano	I-Device
.	O
</s>
<s>
The	O
x86-64	B-Device
architecture	O
was	O
quickly	O
adopted	O
for	O
desktop	O
and	O
laptop	O
personal	O
computers	O
and	O
servers	O
which	O
were	O
commonly	O
configured	O
for	O
16GB	O
of	O
memory	O
or	O
more	O
.	O
</s>
<s>
It	O
is	O
now	O
replacing	O
the	O
discontinued	O
Intel	B-General_Concept
Itanium	I-General_Concept
architecture	I-General_Concept
(	O
formerly	O
IA-64	B-General_Concept
)	O
which	O
was	O
originally	O
intended	O
to	O
eventually	O
replace	O
x86	B-Operating_System
.	O
</s>
<s>
The	O
architectures	O
are	O
not	O
compatible	O
on	O
the	O
native	O
instruction	B-General_Concept
set	I-General_Concept
level	O
,	O
and	O
operating	B-General_Concept
systems	I-General_Concept
and	O
applications	O
compiled	B-Language
for	O
one	O
cannot	O
be	O
run	O
on	O
the	O
other	O
.	O
</s>
<s>
AMD64	B-Device
(	O
also	O
variously	O
referred	O
to	O
by	O
AMD	O
in	O
their	O
literature	O
and	O
documentation	O
as	O
“	O
AMD	O
64-bit	O
Technology	O
”	O
and	O
“	O
AMD	O
x86-64	B-Device
Architecture	O
”	O
)	O
was	O
created	O
as	O
an	O
alternative	O
to	O
the	O
radically	O
different	O
IA-64	B-General_Concept
architecture	O
designed	O
by	O
Intel	O
and	O
Hewlett-Packard	O
,	O
which	O
was	O
backward-incompatible	B-General_Concept
with	O
IA-32	B-Device
,	O
the	O
32-bit	O
version	O
of	O
the	O
x86	B-Operating_System
architecture	I-Operating_System
.	O
</s>
<s>
AMD	O
originally	O
announced	O
AMD64	B-Device
in	O
1999	O
with	O
a	O
full	O
specification	O
available	O
in	O
August	O
2000	O
.	O
</s>
<s>
As	O
AMD	O
was	O
never	O
invited	O
to	O
be	O
a	O
contributing	O
party	O
for	O
the	O
IA-64	B-General_Concept
architecture	O
and	O
any	O
kind	O
of	O
licensing	O
seemed	O
unlikely	O
,	O
the	O
AMD64	B-Device
architecture	O
was	O
positioned	O
by	O
AMD	O
from	O
the	O
beginning	O
as	O
an	O
evolutionary	O
way	O
to	O
add	O
64-bit	B-Device
computing	I-Device
capabilities	O
to	O
the	O
existing	O
x86	B-Operating_System
architecture	I-Operating_System
while	O
supporting	O
legacy	O
32-bit	B-Device
x86	I-Device
code	B-Application
,	O
as	O
opposed	O
to	O
Intel	O
's	O
approach	O
of	O
creating	O
an	O
entirely	O
new	O
,	O
completely	O
x86-incompatible	O
64-bit	B-Device
architecture	I-Device
with	O
IA-64	B-General_Concept
.	O
</s>
<s>
The	O
first	O
AMD64-based	O
processor	O
,	O
the	O
Opteron	B-General_Concept
,	O
was	O
released	O
in	O
April	O
2003	O
.	O
</s>
<s>
AMD	O
's	O
processors	O
implementing	O
the	O
AMD64	B-Device
architecture	O
include	O
Opteron	B-General_Concept
,	O
Athlon	O
64	O
,	O
Athlon	O
64	O
X2	O
,	O
Athlon	O
64	O
FX	O
,	O
Athlon	O
II	O
(	O
followed	O
by	O
"	O
X2	O
"	O
,	O
"	O
X3	O
"	O
,	O
or	O
"	O
X4	O
"	O
to	O
indicate	O
the	O
number	O
of	O
cores	O
,	O
and	O
XLT	O
models	O
)	O
,	O
Turion	O
64	O
,	O
Turion	O
64	O
X2	O
,	O
Sempron	O
(	O
"	O
Palermo	O
"	O
E6	O
stepping	B-General_Concept
and	O
all	O
"	O
Manila	O
"	O
models	O
)	O
,	O
Phenom	O
(	O
followed	O
by	O
"	O
X3	O
"	O
or	O
"	O
X4	O
"	O
to	O
indicate	O
the	O
number	O
of	O
cores	O
)	O
,	O
Phenom	O
II	O
(	O
followed	O
by	O
"	O
X2	O
"	O
,	O
"	O
X3	O
"	O
,	O
"	O
X4	O
"	O
or	O
"	O
X6	O
"	O
to	O
indicate	O
the	O
number	O
of	O
cores	O
)	O
,	O
FX	O
,	O
Fusion/APU	B-Architecture
and	O
Ryzen/Epyc	O
.	O
</s>
<s>
The	O
primary	O
defining	O
characteristic	O
of	O
AMD64	B-Device
is	O
the	O
availability	O
of	O
64-bit	B-Application
general-purpose	O
processor	B-General_Concept
registers	I-General_Concept
(	O
for	O
example	O
,	O
)	O
,	O
64-bit	B-Application
integer	O
arithmetic	O
and	O
logical	O
operations	O
,	O
and	O
64-bit	B-Application
virtual	B-Application
addresses	I-Application
.	O
</s>
<s>
Notable	O
changes	O
in	O
the	O
64-bit	B-Application
extensions	O
include	O
:	O
</s>
<s>
All	O
general-purpose	B-General_Concept
registers	I-General_Concept
(	O
GPRs	B-General_Concept
)	O
are	O
expanded	O
from	O
32bits	O
to	O
64bits	B-Device
,	O
and	O
all	O
arithmetic	O
and	O
logical	O
operations	O
,	O
memory-to-register	O
and	O
register-to-memory	O
operations	O
,	O
etc.	O
,	O
can	O
operate	O
directly	O
on	O
64-bit	B-Application
integers	O
.	O
</s>
<s>
Pushes	B-Application
and	I-Application
pops	I-Application
on	O
the	O
stack	B-General_Concept
default	O
to	O
8-byte	O
strides	O
,	O
and	O
pointers	O
are	O
8	O
bytes	B-Application
wide	O
.	O
</s>
<s>
In	O
addition	O
to	O
increasing	O
the	O
size	O
of	O
the	O
general-purpose	B-General_Concept
registers	I-General_Concept
,	O
the	O
number	O
of	O
named	O
general-purpose	B-General_Concept
registers	I-General_Concept
is	O
increased	O
from	O
eight	O
(	O
i.e.	O
</s>
<s>
,	O
,	O
,	O
,	O
,	O
,	O
,	O
)	O
in	O
x86	B-Operating_System
to	O
16	O
(	O
i.e.	O
</s>
<s>
It	O
is	O
therefore	O
possible	O
to	O
keep	O
more	O
local	O
variables	O
in	O
registers	O
rather	O
than	O
on	O
the	O
stack	B-General_Concept
,	O
and	O
to	O
let	O
registers	O
hold	O
frequently	O
accessed	O
constants	O
;	O
arguments	O
for	O
small	O
and	O
fast	O
subroutines	O
may	O
also	O
be	O
passed	O
in	O
registers	O
to	O
a	O
greater	O
extent	O
.	O
</s>
<s>
AMD64	B-Device
still	O
has	O
fewer	O
registers	O
than	O
many	O
RISC	B-Architecture
instruction	I-Architecture
sets	I-Architecture
(	O
e.g.	O
</s>
<s>
PA-RISC	B-Device
,	O
Power	B-Architecture
ISA	I-Architecture
,	O
and	O
MIPS	B-Device
have	O
32	O
GPRs	B-General_Concept
;	O
Alpha	B-Device
,	O
64-bit	B-Application
ARM	O
,	O
and	O
SPARC	B-Architecture
have	O
31	O
)	O
or	O
VLIW-like	O
machines	O
such	O
as	O
the	O
IA-64	B-General_Concept
(	O
which	O
has	O
128registers	O
)	O
.	O
</s>
<s>
However	O
,	O
an	O
AMD64	B-Device
implementation	O
may	O
have	O
far	O
more	O
internal	O
registers	O
than	O
the	O
number	O
of	O
architectural	O
registers	O
exposed	O
by	O
the	O
instruction	B-General_Concept
set	I-General_Concept
(	O
see	O
register	B-Architecture
renaming	I-Architecture
)	O
.	O
</s>
<s>
(	O
For	O
example	O
,	O
AMD	O
Zen	O
cores	O
have	O
168	O
64-bit	B-Application
integer	O
and	O
160	O
128-bit	O
vector	O
floating-point	B-Algorithm
physical	O
internal	O
registers	O
.	O
)	O
</s>
<s>
Similarly	O
,	O
the	O
number	O
of	O
128-bit	O
XMM	O
registers	O
(	O
used	O
for	O
Streaming	B-General_Concept
SIMD	I-General_Concept
instructions	O
)	O
is	O
also	O
increased	O
from	O
8	O
to	O
16	O
.	O
</s>
<s>
The	O
traditional	O
x87	B-Application
FPU	I-Application
register	O
stack	B-General_Concept
is	O
not	O
included	O
in	O
the	O
register	B-General_Concept
file	I-General_Concept
size	O
extension	O
in	O
64-bit	B-Application
mode	O
,	O
compared	O
with	O
the	O
XMM	O
registers	O
used	O
by	O
SSE2	B-General_Concept
,	O
which	O
did	O
get	O
extended	O
.	O
</s>
<s>
The	O
x87	B-Application
register	O
stack	B-General_Concept
is	O
not	O
a	O
simple	O
register	B-General_Concept
file	I-General_Concept
although	O
it	O
does	O
allow	O
direct	O
access	O
to	O
individual	O
registers	O
by	O
low	O
cost	O
exchange	O
operations	O
.	O
</s>
<s>
The	O
AMD64	B-Device
architecture	O
defines	O
a	O
64-bit	B-Application
virtual	O
address	O
format	O
,	O
of	O
which	O
the	O
low-order	O
48	O
bits	O
are	O
used	O
in	O
current	O
implementations	O
.	O
</s>
<s>
This	O
allows	O
up	O
to	O
256TB	O
(	O
248	O
bytes	B-Application
)	O
of	O
virtual	O
address	O
space	O
.	O
</s>
<s>
The	O
architecture	O
definition	O
allows	O
this	O
limit	O
to	O
be	O
raised	O
in	O
future	O
implementations	O
to	O
the	O
full	O
64	B-Device
bits	I-Device
,	O
extending	O
the	O
virtual	O
address	O
space	O
to	O
16EB	O
(	O
264	O
bytes	B-Application
)	O
.	O
</s>
<s>
This	O
is	O
compared	O
to	O
just	O
4GB	O
(	O
232	O
bytes	B-Application
)	O
for	O
the	O
x86	B-Operating_System
.	O
</s>
<s>
This	O
means	O
that	O
very	O
large	O
files	O
can	O
be	O
operated	O
on	O
by	O
mapping	B-General_Concept
the	O
entire	O
file	O
into	O
the	O
process	O
's	O
address	O
space	O
(	O
which	O
is	O
often	O
much	O
faster	O
than	O
working	O
with	O
file	O
read/write	O
calls	O
)	O
,	O
rather	O
than	O
having	O
to	O
map	O
regions	O
of	O
the	O
file	O
into	O
and	O
out	O
of	O
the	O
address	O
space	O
.	O
</s>
<s>
The	O
original	O
implementation	O
of	O
the	O
AMD64	B-Device
architecture	O
implemented	O
40-bit	O
physical	O
addresses	O
and	O
so	O
could	O
address	O
up	O
to	O
1TB	O
(	O
240	O
bytes	B-Application
)	O
of	O
RAM	O
.	O
</s>
<s>
Current	O
implementations	O
of	O
the	O
AMD64	B-Device
architecture	O
(	O
starting	O
from	O
AMD	O
10h	O
microarchitecture	B-General_Concept
)	O
extend	O
this	O
to	O
48-bit	O
physical	O
addresses	O
and	O
therefore	O
can	O
address	O
up	O
to	O
256TB	O
(	O
248	O
bytes	B-Application
)	O
of	O
RAM	O
.	O
</s>
<s>
The	O
architecture	O
permits	O
extending	O
this	O
to	O
52	O
bits	O
in	O
the	O
future	O
(	O
limited	O
by	O
the	O
page	B-General_Concept
table	I-General_Concept
entry	O
format	O
)	O
;	O
this	O
would	O
allow	O
addressing	O
of	O
up	O
to	O
4PB	O
of	O
RAM	O
.	O
</s>
<s>
For	O
comparison	O
,	O
32-bit	B-Device
x86	I-Device
processors	O
are	O
limited	O
to	O
64GB	O
of	O
RAM	O
in	O
Physical	B-General_Concept
Address	I-General_Concept
Extension	I-General_Concept
(	O
PAE	O
)	O
mode	O
,	O
or	O
4GB	O
of	O
RAM	O
without	O
PAE	O
mode	O
.	O
</s>
<s>
When	O
operating	O
in	O
legacy	B-Device
mode	I-Device
the	O
AMD64	B-Device
architecture	O
supports	O
Physical	B-General_Concept
Address	I-General_Concept
Extension	I-General_Concept
(	O
PAE	O
)	O
mode	O
,	O
as	O
do	O
most	O
current	O
x86	B-Operating_System
processors	O
,	O
but	O
AMD64	B-Device
extends	O
PAE	O
from	O
36	O
bits	O
to	O
an	O
architectural	O
limit	O
of	O
52bits	O
of	O
physical	B-General_Concept
address	I-General_Concept
.	O
</s>
<s>
Any	O
implementation	O
,	O
therefore	O
,	O
allows	O
the	O
same	O
physical	B-General_Concept
address	I-General_Concept
limit	O
as	O
under	O
long	B-Application
mode	I-Application
.	O
</s>
<s>
This	O
makes	O
position-independent	B-Operating_System
code	I-Operating_System
,	O
as	O
is	O
often	O
used	O
in	O
shared	O
libraries	O
and	O
code	B-Application
loaded	O
at	O
run	O
time	O
,	O
more	O
efficient	O
.	O
</s>
<s>
The	O
original	O
AMD64	B-Device
architecture	O
adopted	O
Intel	O
's	O
SSE	B-General_Concept
and	O
SSE2	B-General_Concept
as	O
core	O
instructions	O
.	O
</s>
<s>
These	O
instruction	B-General_Concept
sets	I-General_Concept
provide	O
a	O
vector	O
supplement	O
to	O
the	O
scalar	O
x87	B-Application
FPU	I-Application
,	O
for	O
the	O
single-precision	O
and	O
double-precision	O
data	O
types	O
.	O
</s>
<s>
SSE2	B-General_Concept
also	O
offers	O
integer	O
vector	O
operations	O
,	O
for	O
data	O
types	O
ranging	O
from	O
8bit	O
to	O
64bit	B-Device
precision	O
.	O
</s>
<s>
This	O
makes	O
the	O
vector	O
capabilities	O
of	O
the	O
architecture	O
on	O
par	O
with	O
those	O
of	O
the	O
most	O
advanced	O
x86	B-Operating_System
processors	O
of	O
its	O
time	O
.	O
</s>
<s>
The	O
proliferation	O
of	O
64-bit	B-Device
processors	I-Device
has	O
made	O
these	O
vector	O
capabilities	O
ubiquitous	O
in	O
home	O
computers	O
,	O
allowing	O
the	O
improvement	O
of	O
the	O
standards	O
of	O
32-bit	O
applications	O
.	O
</s>
<s>
The	O
32-bit	O
edition	O
of	O
Windows	B-Application
8	O
,	O
for	O
example	O
,	O
requires	O
the	O
presence	O
of	O
SSE2	B-General_Concept
instructions	O
.	O
</s>
<s>
SSE3	B-General_Concept
instructions	O
and	O
later	O
Streaming	B-General_Concept
SIMD	I-General_Concept
Extensions	I-General_Concept
instruction	B-General_Concept
sets	I-General_Concept
are	O
not	O
standard	O
features	O
of	O
the	O
architecture	O
.	O
</s>
<s>
The	O
No-Execute	B-General_Concept
bit	I-General_Concept
or	O
NX	B-General_Concept
bit	I-General_Concept
(	O
bit	O
63	O
of	O
the	O
page	B-General_Concept
table	I-General_Concept
entry	O
)	O
allows	O
the	O
operating	B-General_Concept
system	I-General_Concept
to	O
specify	O
which	O
pages	O
of	O
virtual	O
address	O
space	O
can	O
contain	O
executable	B-Application
code	I-Application
and	O
which	O
cannot	O
.	O
</s>
<s>
An	O
attempt	O
to	O
execute	O
code	B-Application
from	O
a	O
page	B-Architecture
tagged	O
"	O
no	B-General_Concept
execute	I-General_Concept
"	O
will	O
result	O
in	O
a	O
memory	O
access	O
violation	O
,	O
similar	O
to	O
an	O
attempt	O
to	O
write	O
to	O
a	O
read-only	O
page	B-Architecture
.	O
</s>
<s>
This	O
should	O
make	O
it	O
more	O
difficult	O
for	O
malicious	O
code	B-Application
to	O
take	O
control	O
of	O
the	O
system	O
via	O
"	O
buffer	B-General_Concept
overrun	I-General_Concept
"	O
or	O
"	O
unchecked	O
buffer	O
"	O
attacks	O
.	O
</s>
<s>
A	O
similar	O
feature	O
has	O
been	O
available	O
on	O
x86	B-Operating_System
processors	O
since	O
the	O
80286	B-General_Concept
as	O
an	O
attribute	O
of	O
segment	B-Operating_System
descriptors	I-Operating_System
;	O
however	O
,	O
this	O
works	O
only	O
on	O
an	O
entire	O
segment	O
at	O
a	O
time	O
.	O
</s>
<s>
Segmented	B-Device
addressing	I-Device
has	O
long	O
been	O
considered	O
an	O
obsolete	O
mode	O
of	O
operation	O
,	O
and	O
all	O
current	O
PC	O
operating	B-General_Concept
systems	I-General_Concept
in	O
effect	O
bypass	O
it	O
,	O
setting	O
all	O
segments	O
to	O
a	O
base	O
address	O
of	O
zero	O
and	O
(	O
in	O
their	O
32-bit	O
implementation	O
)	O
a	O
size	O
of	O
4	O
GB	O
.	O
</s>
<s>
AMD	O
was	O
the	O
first	O
x86-family	O
vendor	O
to	O
implement	O
no-execute	O
in	O
linear	O
addressing	B-Language
mode	I-Language
.	O
</s>
<s>
The	O
feature	O
is	O
also	O
available	O
in	O
legacy	B-Device
mode	I-Device
on	O
AMD64	B-Device
processors	O
,	O
and	O
recent	O
Intel	B-Operating_System
x86	I-Operating_System
processors	O
,	O
when	O
PAE	O
is	O
used	O
.	O
</s>
<s>
A	O
few	O
"	O
system	B-Application
programming	I-Application
"	O
features	O
of	O
the	O
x86	B-Operating_System
architecture	I-Operating_System
were	O
either	O
unused	O
or	O
underused	O
in	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
and	O
are	O
either	O
not	O
available	O
on	O
AMD64	B-Device
in	O
long	O
(	O
64-bit	B-Application
and	O
compatibility	O
)	O
mode	O
,	O
or	O
exist	O
only	O
in	O
limited	O
form	O
.	O
</s>
<s>
These	O
include	O
segmented	B-Device
addressing	I-Device
(	O
although	O
the	O
FS	B-Device
and	I-Device
GS	I-Device
segments	O
are	O
retained	O
in	O
vestigial	O
form	O
for	O
use	O
as	O
extra-base	O
pointers	O
to	O
operating	B-General_Concept
system	I-General_Concept
structures	O
)	O
,	O
the	O
task	B-Device
state	I-Device
switch	I-Device
mechanism	O
,	O
and	O
virtual	B-Application
8086	I-Application
mode	I-Application
.	O
</s>
<s>
These	O
features	O
remain	O
fully	O
implemented	O
in	O
"	O
legacy	B-Device
mode	I-Device
"	O
,	O
allowing	O
these	O
processors	O
to	O
run	O
32-bit	O
and	O
16-bit	O
operating	B-General_Concept
systems	I-General_Concept
without	O
modifications	O
.	O
</s>
<s>
Some	O
instructions	O
that	O
proved	O
to	O
be	O
rarely	O
useful	O
are	O
not	O
supported	O
in	O
64-bit	B-Application
mode	O
,	O
including	O
saving/restoring	O
of	O
segment	B-Device
registers	I-Device
on	O
the	O
stack	B-General_Concept
,	O
saving/restoring	O
of	O
all	O
registers	O
(	O
PUSHA/POPA	O
)	O
,	O
decimal	O
arithmetic	O
,	O
BOUND	O
and	O
INTO	O
instructions	O
,	O
and	O
"	O
far	O
"	O
jumps	O
and	O
calls	O
with	O
immediate	O
operands	O
.	O
</s>
<s>
Although	O
virtual	B-Application
addresses	I-Application
are	O
64bits	B-Device
wide	O
in	O
64-bit	B-Application
mode	O
,	O
current	O
implementations	O
(	O
and	O
all	O
chips	O
that	O
are	O
known	O
to	O
be	O
in	O
the	O
planning	O
stages	O
)	O
do	O
not	O
allow	O
the	O
entire	O
virtual	O
address	O
space	O
of	O
264	O
bytes	B-Application
(	O
16EB	O
)	O
to	O
be	O
used	O
.	O
</s>
<s>
Most	O
operating	B-General_Concept
systems	I-General_Concept
and	O
applications	O
will	O
not	O
need	O
such	O
a	O
large	O
address	O
space	O
for	O
the	O
foreseeable	O
future	O
,	O
so	O
implementing	O
such	O
wide	O
virtual	B-Application
addresses	I-Application
would	O
simply	O
increase	O
the	O
complexity	O
and	O
cost	O
of	O
address	O
translation	O
with	O
no	O
real	O
benefit	O
.	O
</s>
<s>
AMD	O
,	O
therefore	O
,	O
decided	O
that	O
,	O
in	O
the	O
first	O
implementations	O
of	O
the	O
architecture	O
,	O
only	O
the	O
least	O
significant	O
48bits	O
of	O
a	O
virtual	O
address	O
would	O
actually	O
be	O
used	O
in	O
address	O
translation	O
(	O
page	B-General_Concept
table	I-General_Concept
lookup	O
)	O
.	O
</s>
<s>
This	O
feature	O
eases	O
later	O
scalability	O
to	O
true	O
64-bit	B-Application
addressing	O
.	O
</s>
<s>
Many	O
operating	B-General_Concept
systems	I-General_Concept
(	O
including	O
,	O
but	O
not	O
limited	O
to	O
,	O
the	O
Windows	B-Device
NT	I-Device
family	I-Device
)	O
take	O
the	O
higher-addressed	O
half	O
of	O
the	O
address	O
space	O
(	O
named	O
kernel	B-Operating_System
space	I-Operating_System
)	O
for	O
themselves	O
and	O
leave	O
the	O
lower-addressed	O
half	O
(	O
user	B-Operating_System
space	I-Operating_System
)	O
for	O
application	O
code	B-Application
,	O
user	B-Operating_System
mode	I-Operating_System
stacks	B-Application
,	O
heaps	O
,	O
and	O
other	O
data	O
regions	O
.	O
</s>
<s>
The	O
"	O
canonical	O
address	O
"	O
design	O
ensures	O
that	O
every	O
AMD64	B-Device
compliant	O
implementation	O
has	O
,	O
in	O
effect	O
,	O
two	O
memory	O
halves	O
:	O
the	O
lower	O
half	O
starts	O
at	O
00000000'00000000	O
and	O
"	O
grows	O
upwards	O
"	O
as	O
more	O
virtual	O
address	O
bits	O
become	O
available	O
,	O
while	O
the	O
higher	O
half	O
is	O
"	O
docked	O
"	O
to	O
the	O
top	O
of	O
the	O
address	O
space	O
and	O
grows	O
downwards	O
.	O
</s>
<s>
Also	O
,	O
enforcing	O
the	O
"	O
canonical	O
form	O
"	O
of	O
addresses	O
by	O
checking	O
the	O
unused	O
address	O
bits	O
prevents	O
their	O
use	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
in	O
tagged	O
pointers	O
as	O
flags	O
,	O
privilege	O
markers	O
,	O
etc.	O
,	O
as	O
such	O
use	O
could	O
become	O
problematic	O
when	O
the	O
architecture	O
is	O
extended	O
to	O
implement	O
more	O
virtual	O
address	O
bits	O
.	O
</s>
<s>
The	O
first	O
versions	O
of	O
Windows	B-Application
for	O
x64	B-Device
did	O
not	O
even	O
use	O
the	O
full	O
256TB	O
;	O
they	O
were	O
restricted	O
to	O
just	O
8TB	O
of	O
user	B-Operating_System
space	I-Operating_System
and	O
8TB	O
of	O
kernel	B-Operating_System
space	I-Operating_System
.	O
</s>
<s>
Windows	B-Application
did	O
not	O
support	O
the	O
entire	O
48-bit	O
address	O
space	O
until	O
Windows	B-Application
8.1	B-Device
,	O
which	O
was	O
released	O
in	O
October	O
2013	O
.	O
</s>
<s>
The	O
64-bit	B-Application
addressing	B-Language
mode	I-Language
(	O
"	O
long	B-Application
mode	I-Application
"	O
)	O
is	O
a	O
superset	O
of	O
Physical	B-General_Concept
Address	I-General_Concept
Extensions	I-General_Concept
(	O
PAE	O
)	O
;	O
because	O
of	O
this	O
,	O
page	B-Architecture
sizes	O
may	O
be	O
4KB	O
(	O
212	O
bytes	B-Application
)	O
or	O
2MB	O
(	O
221	O
bytes	B-Application
)	O
.	O
</s>
<s>
Long	B-Application
mode	I-Application
also	O
supports	O
page	B-Architecture
sizes	O
of	O
1GB	O
(	O
230	O
bytes	B-Application
)	O
.	O
</s>
<s>
Rather	O
than	O
the	O
three-level	O
page	B-General_Concept
table	I-General_Concept
system	O
used	O
by	O
systems	O
in	O
PAE	O
mode	O
,	O
systems	O
running	O
in	O
long	B-Application
mode	I-Application
use	O
four	O
levels	O
of	O
page	B-General_Concept
table	I-General_Concept
:	O
PAE	O
's	O
Page-Directory	O
Pointer	O
Table	O
is	O
extended	O
from	O
four	O
entries	O
to	O
512	O
,	O
and	O
an	O
additional	O
Page-Map	O
Level	O
4	O
(	O
PML4	O
)	O
Table	O
is	O
added	O
,	O
containing	O
512	O
entries	O
in	O
48-bit	O
implementations	O
.	O
</s>
<s>
A	O
full	O
mapping	B-General_Concept
hierarchy	O
of	O
4KB	O
pages	O
for	O
the	O
whole	O
48-bit	O
space	O
would	O
take	O
a	O
bit	O
more	O
than	O
512GB	O
of	O
memory	O
(	O
about	O
0.195	O
%	O
of	O
the	O
256TB	O
virtual	O
space	O
)	O
.	O
</s>
<s>
Intel	O
has	O
implemented	O
a	O
scheme	O
with	O
a	O
5-level	B-Device
page	I-Device
table	I-Device
,	O
which	O
allows	O
Intel	O
64	O
processors	O
to	O
support	O
a	O
57-bit	O
virtual	O
address	O
space	O
.	O
</s>
<s>
Further	O
extensions	O
may	O
allow	O
full	O
64-bit	B-Application
virtual	O
address	O
space	O
and	O
physical	O
memory	O
by	O
expanding	O
the	O
page	B-General_Concept
table	I-General_Concept
entry	O
size	O
to	O
128-bit	O
,	O
and	O
reduce	O
page	B-Architecture
walks	O
in	O
the	O
5-level	O
hierarchy	O
by	O
using	O
a	O
larger	O
64KB	O
page	B-Architecture
allocation	O
size	O
that	O
still	O
supports	O
4KB	O
page	B-Architecture
operations	O
for	O
backward	B-General_Concept
compatibility	I-General_Concept
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
can	O
also	O
limit	O
the	O
virtual	O
address	O
space	O
.	O
</s>
<s>
Details	O
,	O
where	O
applicable	O
,	O
are	O
given	O
in	O
the	O
"	O
Operating	B-General_Concept
system	I-General_Concept
compatibility	O
and	O
characteristics	O
"	O
section	O
.	O
</s>
<s>
Current	O
AMD64	B-Device
processors	O
support	O
a	O
physical	B-General_Concept
address	I-General_Concept
space	O
of	O
up	O
to	O
248	O
bytes	B-Application
of	O
RAM	O
,	O
or	O
256TB	O
.	O
</s>
<s>
However	O
,	O
,	O
there	O
were	O
no	O
known	O
x86-64	B-Device
motherboards	B-Device
that	O
support	O
256TB	O
of	O
RAM	O
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
may	O
place	O
additional	O
limits	O
on	O
the	O
amount	O
of	O
RAM	O
that	O
is	O
usable	O
or	O
supported	O
.	O
</s>
<s>
Details	O
on	O
this	O
point	O
are	O
given	O
in	O
the	O
"	O
Operating	B-General_Concept
system	I-General_Concept
compatibility	O
and	O
characteristics	O
"	O
section	O
of	O
this	O
article	O
.	O
</s>
<s>
The	O
architecture	O
has	O
two	O
primary	O
modes	O
of	O
operation	O
:	O
long	B-Application
mode	I-Application
and	O
legacy	B-Device
mode	I-Device
.	O
</s>
<s>
Operating	O
Operating	B-General_Concept
system	I-General_Concept
required	O
Type	O
of	O
code	B-Application
being	O
run	O
Size	O
(	O
in	O
bits	O
)	O
No	O
.	O
</s>
<s>
Long	B-Application
mode	I-Application
is	O
the	O
architecture	O
's	O
intended	O
primary	O
mode	O
of	O
operation	O
;	O
it	O
is	O
a	O
combination	O
of	O
the	O
processor	O
's	O
native	O
64-bit	B-Application
mode	O
and	O
a	O
combined	O
32-bit	O
and	O
16-bit	O
compatibility	O
mode	O
.	O
</s>
<s>
It	O
is	O
used	O
by	O
64-bit	B-Application
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Under	O
a	O
64-bit	B-Application
operating	B-General_Concept
system	I-General_Concept
,	O
64-bit	B-Application
programs	O
run	O
under	O
64-bit	B-Application
mode	O
,	O
and	O
32-bit	O
and	O
16-bit	O
protected	B-Application
mode	I-Application
applications	O
(	O
that	O
do	O
not	O
need	O
to	O
use	O
either	O
real	B-Application
mode	I-Application
or	O
virtual	B-Application
8086	I-Application
mode	I-Application
in	O
order	O
to	O
execute	O
at	O
any	O
time	O
)	O
run	O
under	O
compatibility	O
mode	O
.	O
</s>
<s>
Real-mode	B-Application
programs	O
and	O
programs	O
that	O
use	O
virtual	B-Application
8086	I-Application
mode	I-Application
at	O
any	O
time	O
cannot	O
be	O
run	O
in	O
long	B-Application
mode	I-Application
unless	O
those	O
modes	O
are	O
emulated	O
in	O
software	O
.	O
</s>
<s>
However	O
,	O
such	O
programs	O
may	O
be	O
started	O
from	O
an	O
operating	B-General_Concept
system	I-General_Concept
running	O
in	O
long	B-Application
mode	I-Application
on	O
processors	O
supporting	O
VT-x	O
or	O
AMD-V	O
by	O
creating	O
a	O
virtual	O
processor	O
running	O
in	O
the	O
desired	O
mode	O
.	O
</s>
<s>
Since	O
the	O
basic	O
instruction	B-General_Concept
set	I-General_Concept
is	O
the	O
same	O
,	O
there	O
is	O
almost	O
no	O
performance	O
penalty	O
for	O
executing	O
protected	B-Application
mode	I-Application
x86	B-Operating_System
code	B-Application
.	O
</s>
<s>
This	O
is	O
unlike	O
Intel	O
's	O
IA-64	B-General_Concept
,	O
where	O
differences	O
in	O
the	O
underlying	O
instruction	B-General_Concept
set	I-General_Concept
mean	O
that	O
running	O
32-bit	O
code	B-Application
must	O
be	O
done	O
either	O
in	O
emulation	O
of	O
x86	B-Operating_System
(	O
making	O
the	O
process	O
slower	O
)	O
or	O
with	O
a	O
dedicated	O
x86	B-Operating_System
coprocessor	O
.	O
</s>
<s>
However	O
,	O
on	O
the	O
x86-64	B-Device
platform	O
,	O
many	O
x86	B-Operating_System
applications	O
could	O
benefit	O
from	O
a	O
64-bit	B-Application
recompile	B-Language
,	O
due	O
to	O
the	O
additional	O
registers	O
in	O
64-bit	B-Application
code	B-Application
and	O
guaranteed	O
SSE2-based	O
FPU	B-Application
support	O
,	O
which	O
a	O
compiler	B-Language
can	O
use	O
for	O
optimization	O
.	O
</s>
<s>
However	O
,	O
applications	O
that	O
regularly	O
handle	O
integers	O
wider	O
than	O
32	O
bits	O
,	O
such	O
as	O
cryptographic	O
algorithms	O
,	O
will	O
need	O
a	O
rewrite	O
of	O
the	O
code	B-Application
handling	O
the	O
huge	O
integers	O
in	O
order	O
to	O
take	O
advantage	O
of	O
the	O
64-bit	B-Application
registers	O
.	O
</s>
<s>
Legacy	B-Device
mode	I-Device
is	O
the	O
mode	O
that	O
the	O
processor	O
is	O
in	O
when	O
it	O
is	O
not	O
in	O
long	B-Application
mode	I-Application
.	O
</s>
<s>
In	O
this	O
mode	O
,	O
the	O
processor	O
acts	O
like	O
an	O
older	O
x86	B-Operating_System
processor	O
,	O
and	O
only	O
16-bit	O
and	O
32-bit	O
code	B-Application
can	O
be	O
executed	O
.	O
</s>
<s>
Legacy	B-Device
mode	I-Device
allows	O
for	O
a	O
maximum	O
of	O
32bit	O
virtual	O
addressing	O
which	O
limits	O
the	O
virtual	O
address	O
space	O
to	O
4GB	O
.	O
</s>
<s>
64-bit	B-Application
programs	O
cannot	O
be	O
run	O
from	O
legacy	B-Device
mode	I-Device
.	O
</s>
<s>
Protected	B-Application
mode	I-Application
is	O
made	O
into	O
a	O
submode	O
of	O
legacy	B-Device
mode	I-Device
.	O
</s>
<s>
It	O
is	O
the	O
submode	O
that	O
32-bit	O
operating	B-General_Concept
systems	I-General_Concept
and	O
16-bit	O
protected	B-Application
mode	I-Application
operating	B-General_Concept
systems	I-General_Concept
operate	O
in	O
when	O
running	O
on	O
an	O
x86-64	B-Device
CPU	O
.	O
</s>
<s>
Real	B-Application
mode	I-Application
is	O
the	O
initial	O
mode	O
of	O
operation	O
when	O
the	O
processor	O
is	O
initialized	O
,	O
and	O
is	O
a	O
submode	O
of	O
legacy	B-Device
mode	I-Device
.	O
</s>
<s>
It	O
is	O
backwards	B-General_Concept
compatible	I-General_Concept
with	O
the	O
original	O
Intel	B-General_Concept
8086	I-General_Concept
and	O
Intel	B-Device
8088	I-Device
processors	O
.	O
</s>
<s>
Real	B-Application
mode	I-Application
is	O
primarily	O
used	O
today	O
by	O
operating	B-General_Concept
system	I-General_Concept
bootloaders	B-Application
,	O
which	O
are	O
required	O
by	O
the	O
architecture	O
to	O
configure	O
virtual	B-Architecture
memory	I-Architecture
details	O
before	O
transitioning	O
to	O
higher	O
modes	O
.	O
</s>
<s>
This	O
mode	O
is	O
also	O
used	O
by	O
any	O
operating	B-General_Concept
system	I-General_Concept
that	O
needs	O
to	O
communicate	O
with	O
the	O
system	O
firmware	O
with	O
a	O
traditional	O
BIOS-style	O
interface	O
.	O
</s>
<s>
Intel	O
64	O
is	O
Intel	O
's	O
implementation	O
of	O
x86-64	B-Device
,	O
used	O
and	O
implemented	O
in	O
various	O
processors	O
made	O
by	O
Intel	O
.	O
</s>
<s>
Historically	O
,	O
AMD	O
has	O
developed	O
and	O
produced	O
processors	O
with	O
instruction	B-General_Concept
sets	I-General_Concept
patterned	O
after	O
Intel	O
's	O
original	O
designs	O
,	O
but	O
with	O
x86-64	B-Device
,	O
roles	O
were	O
reversed	O
:	O
Intel	O
found	O
itself	O
in	O
the	O
position	O
of	O
adopting	O
the	O
ISA	B-General_Concept
that	O
AMD	O
created	O
as	O
an	O
extension	O
to	O
Intel	O
's	O
own	O
x86	B-Operating_System
processor	O
line	O
.	O
</s>
<s>
Intel	O
's	O
name	O
for	O
this	O
instruction	B-General_Concept
set	I-General_Concept
has	O
changed	O
several	O
times	O
.	O
</s>
<s>
The	O
name	O
used	O
at	O
the	O
IDF	O
was	O
CT	O
(	O
presumably	O
for	O
Clackamas	O
Technology	O
,	O
another	O
codename	O
from	O
an	O
Oregon	O
river	O
)	O
;	O
within	O
weeks	O
they	O
began	O
referring	O
to	O
it	O
as	O
IA-32e	B-Device
(	O
for	O
IA-32	B-Device
extensions	O
)	O
and	O
in	O
March	O
2004	O
unveiled	O
the	O
"	O
official	O
"	O
name	O
EM64T	B-Device
(	O
Extended	O
Memory	O
64	O
Technology	O
)	O
.	O
</s>
<s>
In	O
late	O
2006	O
Intel	O
began	O
instead	O
using	O
the	O
name	O
Intel	O
64	O
for	O
its	O
implementation	O
,	O
paralleling	O
AMD	O
's	O
use	O
of	O
the	O
name	O
AMD64	B-Device
.	O
</s>
<s>
The	O
first	O
processor	O
to	O
implement	O
Intel64	B-Device
was	O
the	O
multi-socket	O
processor	O
Xeon	B-Device
code-named	O
Nocona	O
in	O
June	O
2004	O
.	O
</s>
<s>
Intel	O
subsequently	O
began	O
selling	O
Intel64-enabled	O
Pentium	B-General_Concept
4s	I-General_Concept
using	O
the	O
E0	O
revision	O
of	O
the	O
Prescott	O
core	O
,	O
being	O
sold	O
on	O
the	O
OEM	O
market	O
as	O
the	O
Pentium	B-General_Concept
4	I-General_Concept
,	O
model	O
F	O
.	O
The	O
E0	O
revision	O
also	O
adds	O
eXecute	O
Disable	O
(	O
XD	O
)	O
(	O
Intel	O
's	O
name	O
for	O
the	O
NX	B-General_Concept
bit	I-General_Concept
)	O
to	O
Intel64	B-Device
,	O
and	O
has	O
been	O
included	O
in	O
then	O
current	O
Xeon	B-Device
code-named	O
Irwindale	O
.	O
</s>
<s>
Intel	O
's	O
official	O
launch	O
of	O
Intel64	B-Device
(	O
under	O
the	O
name	O
EM64T	B-Device
at	O
that	O
time	O
)	O
in	O
mainstream	O
desktop	O
processors	O
was	O
the	O
N0	O
stepping	B-General_Concept
Prescott-2M	O
.	O
</s>
<s>
The	O
first	O
Intel	O
mobile	B-General_Concept
processor	I-General_Concept
implementing	O
Intel64	B-Device
is	O
the	O
Merom	B-Device
version	O
of	O
the	O
Core	B-Device
2	I-Device
processor	O
,	O
which	O
was	O
released	O
on	O
July	O
27	O
,	O
2006	O
.	O
</s>
<s>
None	O
of	O
Intel	O
's	O
earlier	O
notebook	O
CPUs	O
(	O
Core	O
Duo	O
,	O
Pentium	B-Architecture
M	I-Architecture
,	O
Celeron	B-Device
M	O
,	O
Mobile	B-General_Concept
Pentium	I-General_Concept
4	I-General_Concept
)	O
implement	O
Intel64	B-Device
.	O
</s>
<s>
Intel	O
's	O
processors	O
implementing	O
the	O
Intel64	B-Device
architecture	O
include	O
the	O
Pentium	B-General_Concept
4	I-General_Concept
F-series/5x1	O
series	O
,	O
506	O
,	O
and	O
516	O
,	O
Celeron	B-Device
D	O
models	O
3x1	O
,	O
3x6	O
,	O
355	O
,	O
347	O
,	O
352	O
,	O
360	O
,	O
and	O
365	O
and	O
all	O
later	O
Celerons	B-Device
,	O
all	O
models	O
of	O
Xeon	B-Device
since	O
"	O
Nocona	O
"	O
,	O
all	O
models	O
of	O
Pentium	B-Device
Dual-Core	I-Device
processors	O
since	O
"	O
Merom-2M	O
"	O
,	O
the	O
Atom	B-Device
230	O
,	O
330	O
,	O
D410	O
,	O
D425	O
,	O
D510	O
,	O
D525	O
,	O
N450	O
,	O
N455	O
,	O
N470	O
,	O
N475	O
,	O
N550	O
,	O
N570	O
,	O
N2600	O
and	O
N2800	O
,	O
all	O
versions	O
of	O
the	O
Pentium	B-Device
D	I-Device
,	O
Pentium	B-Device
Extreme	I-Device
Edition	I-Device
,	O
Core	O
2	O
,	O
Core	O
i9	O
,	O
Core	O
i7	O
,	O
Core	O
i5	O
,	O
and	O
Core	O
i3	O
processors	O
,	O
and	O
the	O
Xeon	B-General_Concept
Phi	I-General_Concept
7200	O
series	O
processors	O
.	O
</s>
<s>
VIA	O
Technologies	O
introduced	O
their	O
first	O
implementation	O
of	O
the	O
x86-64	B-Device
architecture	O
in	O
2008	O
after	O
five	O
years	O
of	O
development	O
by	O
its	O
CPU	O
division	O
,	O
Centaur	O
Technology	O
.	O
</s>
<s>
Codenamed	O
"	O
Isaiah	O
"	O
,	O
the	O
64-bit	B-Device
architecture	I-Device
was	O
unveiled	O
on	O
January	O
24	O
,	O
2008	O
,	O
and	O
launched	O
on	O
May	O
29	O
under	O
the	O
VIA	B-Device
Nano	I-Device
brand	O
name	O
.	O
</s>
<s>
The	O
processor	O
supports	O
a	O
number	O
of	O
VIA-specific	O
x86	B-Operating_System
extensions	O
designed	O
to	O
boost	O
efficiency	O
in	O
low-power	O
appliances	O
.	O
</s>
<s>
It	O
is	O
expected	O
that	O
the	O
Isaiah	O
architecture	O
will	O
be	O
twice	O
as	O
fast	O
in	O
integer	O
performance	O
and	O
four	O
times	O
as	O
fast	O
in	O
floating-point	B-Algorithm
performance	O
as	O
the	O
previous-generation	O
VIA	B-Device
Esther	I-Device
at	O
an	O
equivalent	O
clock	O
speed	O
.	O
</s>
<s>
Power	O
consumption	O
is	O
also	O
expected	O
to	O
be	O
on	O
par	O
with	O
the	O
previous-generation	O
VIA	O
CPUs	O
,	O
with	O
thermal	B-General_Concept
design	I-General_Concept
power	I-General_Concept
ranging	O
from	O
5W	O
to	O
25W	O
.	O
</s>
<s>
Being	O
a	O
completely	O
new	O
design	O
,	O
the	O
Isaiah	O
architecture	O
was	O
built	O
with	O
support	O
for	O
features	O
like	O
the	O
x86-64	B-Device
instruction	B-General_Concept
set	I-General_Concept
and	O
x86	B-General_Concept
virtualization	I-General_Concept
which	O
were	O
unavailable	O
on	O
its	O
predecessors	O
,	O
the	O
VIA	B-Device
C7	I-Device
line	O
,	O
while	O
retaining	O
their	O
encryption	O
extensions	O
.	O
</s>
<s>
In	O
2020	O
,	O
through	O
a	O
collaboration	O
between	O
AMD	O
,	O
Intel	O
,	O
Red	O
Hat	O
,	O
and	O
SUSE	O
,	O
three	O
microarchitecture	B-General_Concept
levels	O
on	O
top	O
of	O
the	O
x86-64	B-Device
baseline	O
were	O
defined	O
:	O
x86-64-v2	O
,	O
x86-64-v3	O
,	O
and	O
x86-64-v4	O
.	O
</s>
<s>
These	O
levels	O
define	O
specific	O
features	O
that	O
can	O
be	O
targeted	O
by	O
programmers	O
to	O
provide	O
compile-time	O
optimizations	O
.	O
</s>
<s>
Instruction	B-General_Concept
set	I-General_Concept
extensions	O
not	O
concerned	O
with	O
general-purpose	O
computation	O
,	O
including	O
AES-NI	O
and	O
RDRAND	B-Language
,	O
are	O
excluded	O
from	O
the	O
level	O
requirements	O
.	O
</s>
<s>
Although	O
nearly	O
identical	O
,	O
there	O
are	O
some	O
differences	O
between	O
the	O
two	O
instruction	B-General_Concept
sets	I-General_Concept
in	O
the	O
semantics	O
of	O
a	O
few	O
seldom	O
used	O
machine	B-Language
instructions	I-Language
(	O
or	O
situations	O
)	O
,	O
which	O
are	O
mainly	O
used	O
for	O
system	B-Application
programming	I-Application
.	O
</s>
<s>
Compilers	B-Language
generally	O
produce	O
executables	B-Application
(	O
i.e.	O
</s>
<s>
machine	B-Language
code	I-Language
)	O
that	O
avoid	O
any	O
differences	O
,	O
at	O
least	O
for	O
ordinary	O
application	B-Application
programs	I-Application
.	O
</s>
<s>
This	O
is	O
therefore	O
of	O
interest	O
mainly	O
to	O
developers	O
of	O
compilers	B-Language
,	O
operating	B-General_Concept
systems	I-General_Concept
and	O
similar	O
,	O
which	O
must	O
deal	O
with	O
individual	O
and	O
special	O
system	O
instructions	O
.	O
</s>
<s>
Intel64	B-Device
's	O
BSF	O
and	O
BSR	O
instructions	O
act	O
differently	O
than	O
AMD64	B-Device
's	O
when	O
the	O
source	O
is	O
zero	O
and	O
the	O
operand	O
size	O
is	O
32bits	O
.	O
</s>
<s>
The	O
separate	O
claim	O
about	O
maybe	O
not	O
preserving	O
bits	O
in	O
the	O
upper	O
32	O
has	O
not	O
been	O
verified	O
,	O
but	O
has	O
only	O
been	O
ruled	O
out	O
for	O
Core	B-Device
2	I-Device
and	O
Skylake	O
,	O
not	O
all	O
Intel	O
microarchitectures	B-General_Concept
like	O
64-bit	B-Application
Pentium	B-General_Concept
4	I-General_Concept
or	O
low-power	O
Atom	B-Device
.	O
</s>
<s>
AMD64	B-Device
requires	O
a	O
different	O
microcode	B-Device
update	O
format	O
and	O
control	O
MSRs	O
(	O
model-specific	O
registers	O
)	O
,	O
while	O
Intel64	B-Device
implements	O
microcode	B-Device
update	O
unchanged	O
from	O
their	O
32-bit	O
only	O
processors	O
.	O
</s>
<s>
Intel64	B-Device
lacks	O
some	O
MSRs	O
that	O
are	O
considered	O
architectural	O
in	O
AMD64	B-Device
.	O
</s>
<s>
Intel64	B-Device
allows	O
SYSCALL/SYSRET	O
only	O
in	O
64-bit	B-Application
mode	O
(	O
not	O
in	O
compatibility	O
mode	O
)	O
,	O
and	O
allows	O
SYSENTER/SYSEXIT	O
in	O
both	O
modes	O
.	O
</s>
<s>
AMD64	B-Device
lacks	O
SYSENTER/SYSEXIT	O
in	O
both	O
sub-modes	O
of	O
long	B-Application
mode	I-Application
.	O
</s>
<s>
In	O
64-bit	B-Application
mode	O
,	O
near	O
branches	O
with	O
the	O
66H	O
(	O
operand	O
size	O
override	O
)	O
prefix	O
behave	O
differently	O
.	O
</s>
<s>
Intel64	B-Device
ignores	O
this	O
prefix	O
:	O
the	O
instruction	O
has	O
a	O
32-bit	O
sign	O
extended	O
offset	O
,	O
and	O
instruction	O
pointer	O
is	O
not	O
truncated	O
.	O
</s>
<s>
AMD64	B-Device
uses	O
a	O
16-bit	O
offset	O
field	O
in	O
the	O
instruction	O
,	O
and	O
clears	O
the	O
top	O
48bits	O
of	O
instruction	O
pointer	O
.	O
</s>
<s>
AMD	O
processors	O
raise	O
a	O
floating-point	B-Algorithm
Invalid	O
Exception	O
when	O
performing	O
an	O
FLD	O
or	O
FSTP	O
of	O
an	O
80-bit	O
signalling	O
NaN	O
,	O
while	O
Intel	O
processors	O
do	O
not	O
.	O
</s>
<s>
Intel64	B-Device
lacks	O
the	O
ability	O
to	O
save	O
and	O
restore	O
a	O
reduced	O
(	O
and	O
thus	O
faster	O
)	O
version	O
of	O
the	O
floating-point	B-Algorithm
state	O
(	O
involving	O
the	O
FXSAVE	O
and	O
FXRSTOR	O
instructions	O
)	O
.	O
</s>
<s>
AMD	O
processors	O
ever	O
since	O
Opteron	B-General_Concept
Rev	O
.	O
</s>
<s>
D	O
have	O
reintroduced	O
limited	O
support	O
for	O
segmentation	O
,	O
via	O
the	O
Long	B-Application
Mode	I-Application
Segment	O
Limit	O
Enable	O
(	O
LMSLE	O
)	O
bit	O
,	O
to	O
ease	O
virtualization	O
of	O
64-bit	B-Application
guests	O
.	O
</s>
<s>
When	O
returning	O
to	O
a	O
non-canonical	O
address	O
using	O
SYSRET	O
,	O
AMD64	B-Device
processors	O
execute	O
the	O
general	O
protection	O
fault	O
handler	O
in	O
privilege	O
level	O
3	O
,	O
while	O
on	O
Intel64	B-Device
processors	O
it	O
is	O
executed	O
in	O
privilege	O
level	O
0	O
.	O
</s>
<s>
The	O
AMD64	B-Device
processors	O
prior	O
to	O
Revision	O
F	O
(	O
distinguished	O
by	O
the	O
switch	O
from	O
DDR	O
to	O
DDR2	O
memory	O
and	O
new	O
sockets	O
AM2	O
,	O
F	O
and	O
S1	O
)	O
of	O
2006	O
lacked	O
the	O
CMPXCHG16B	O
instruction	O
,	O
which	O
is	O
an	O
extension	O
of	O
the	O
CMPXCHG8B	O
instruction	O
present	O
on	O
most	O
post-80486	O
processors	O
.	O
</s>
<s>
Similar	O
to	O
CMPXCHG8B	O
,	O
CMPXCHG16B	O
allows	O
for	O
atomic	B-General_Concept
operations	I-General_Concept
on	O
octa-words	O
(	O
128-bit	O
values	O
)	O
.	O
</s>
<s>
This	O
is	O
useful	O
for	O
parallel	O
algorithms	O
that	O
use	O
compare	B-Operating_System
and	I-Operating_System
swap	I-Operating_System
on	O
data	O
larger	O
than	O
the	O
size	O
of	O
a	O
pointer	O
,	O
common	O
in	O
lock-free	B-Operating_System
and	I-Operating_System
wait-free	I-Operating_System
algorithms	I-Operating_System
.	O
</s>
<s>
Without	O
CMPXCHG16B	O
one	O
must	O
use	O
workarounds	O
,	O
such	O
as	O
a	O
critical	B-Operating_System
section	I-Operating_System
or	O
alternative	O
lock-free	B-Operating_System
approaches	O
.	O
</s>
<s>
Its	O
absence	O
also	O
prevents	O
64-bit	B-Application
Windows	B-Application
prior	O
to	O
Windows	B-Device
8.1	I-Device
from	O
having	O
a	O
user-mode	B-Operating_System
address	O
space	O
larger	O
than	O
8TB	O
.	O
</s>
<s>
The	O
64-bit	B-Application
version	O
of	O
Windows	B-Device
8.1	I-Device
requires	O
the	O
instruction	O
.	O
</s>
<s>
Early	O
AMD64	B-Device
and	O
Intel64	B-Device
CPUs	O
lacked	O
LAHF	O
and	O
SAHF	O
instructions	O
in	O
64-bit	B-Application
mode	O
.	O
</s>
<s>
AMD	O
introduced	O
these	O
instructions	O
(	O
also	O
in	O
64-bit	B-Application
mode	O
)	O
with	O
their	O
90	O
nm	O
(	O
revisionD	O
)	O
processors	O
,	O
starting	O
with	O
Athlon64	O
in	O
October	O
2004	O
.	O
</s>
<s>
Intel	O
introduced	O
the	O
instructions	O
in	O
October	O
2005	O
with	O
the	O
0F47h	O
and	O
later	O
revisions	O
of	O
NetBurst	B-Device
.	O
</s>
<s>
The	O
64-bit	B-Application
version	O
of	O
Windows	B-Device
8.1	I-Device
requires	O
this	O
feature	O
.	O
</s>
<s>
Early	O
Intel	O
CPUs	O
with	O
Intel64	B-Device
also	O
lack	O
the	O
NX	B-General_Concept
bit	I-General_Concept
of	O
the	O
AMD64	B-Device
architecture	O
.	O
</s>
<s>
It	O
was	O
added	O
in	O
the	O
stepping	B-General_Concept
E0	O
(	O
0F41h	O
)	O
Pentium	B-General_Concept
4	I-General_Concept
in	O
October	O
2004	O
.	O
</s>
<s>
This	O
feature	O
is	O
required	O
by	O
all	O
versions	O
of	O
Windows	B-Application
8	O
.	O
</s>
<s>
Early	O
Intel64	B-Device
implementations	O
had	O
a	O
36-bit	O
(	O
64GB	O
)	O
physical	O
addressing	O
of	O
memory	O
while	O
original	O
AMD64	B-Device
implementations	O
had	O
a	O
40-bit	O
(	O
1TB	O
)	O
physical	O
addressing	O
.	O
</s>
<s>
Intel	O
used	O
the	O
40-bit	O
physical	O
addressing	O
first	O
on	O
Xeon	B-Device
MP	I-Device
(	O
Potomac	O
)	O
,	O
launched	O
on	O
29	O
March	O
2005	O
.	O
</s>
<s>
In	O
2007	O
AMD	O
10h-based	O
Opteron	B-General_Concept
was	O
the	O
first	O
to	O
provide	O
a	O
48-bit	O
(	O
256TB	O
)	O
physical	B-General_Concept
address	I-General_Concept
space	O
.	O
</s>
<s>
Intel	O
64	O
's	O
physical	O
addressing	O
was	O
extended	O
to	O
44	O
bits	O
(	O
16TB	O
)	O
in	O
Nehalem-EX	O
in	O
2010	O
and	O
to	O
46	O
bits	O
(	O
64TB	O
)	O
in	O
Sandy	O
Bridge	O
E	O
in	O
2011	O
.	O
</s>
<s>
With	O
the	O
Ice	O
Lake	O
3rd	O
gen	O
Xeon	B-Device
Scalable	O
processors	O
,	O
Intel	O
increased	O
the	O
virtual	O
addressing	O
to	O
57	O
bits	O
(	O
128PB	O
)	O
and	O
physical	O
to	O
52	O
bits	O
(	O
4PB	O
)	O
in	O
2021	O
,	O
necessitating	O
a	O
5-level	B-Device
paging	I-Device
.	O
</s>
<s>
The	O
following	O
year	O
AMD64	B-Device
added	O
the	O
same	O
in	O
4th	O
generation	O
EPYC	O
(	O
Genoa	O
)	O
.	O
</s>
<s>
In	O
supercomputers	B-Architecture
tracked	O
by	O
TOP500	B-Operating_System
,	O
the	O
appearance	O
of	O
64-bit	B-Application
extensions	O
for	O
the	O
x86	B-Operating_System
architecture	I-Operating_System
enabled	O
64-bit	B-Device
x86	I-Device
processors	O
by	O
AMD	O
and	O
Intel	O
to	O
replace	O
most	O
RISC	B-Architecture
processor	I-Architecture
architectures	O
previously	O
used	O
in	O
such	O
systems	O
(	O
including	O
PA-RISC	B-Device
,	O
SPARC	B-Architecture
,	O
Alpha	B-Device
and	O
others	O
)	O
,	O
as	O
well	O
as	O
32-bit	B-Device
x86	I-Device
,	O
even	O
though	O
Intel	O
itself	O
initially	O
tried	O
unsuccessfully	O
to	O
replace	O
x86	B-Operating_System
with	O
a	O
new	O
incompatible	O
64-bit	B-Device
architecture	I-Device
in	O
the	O
Itanium	B-General_Concept
processor	O
.	O
</s>
<s>
,	O
a	O
Fujitsu	O
A64FX-based	O
supercomputer	B-Architecture
called	O
Fugaku	B-Device
is	O
number	O
one	O
.	O
</s>
<s>
The	O
first	O
ARM-based	O
supercomputer	B-Architecture
appeared	O
on	O
the	O
list	O
in	O
2018	O
and	O
,	O
in	O
recent	O
years	O
,	O
non-CPU	O
architecture	O
co-processors	O
(	O
GPGPU	B-Architecture
)	O
have	O
also	O
played	O
a	O
big	O
role	O
in	O
performance	O
.	O
</s>
<s>
Intel	O
's	O
Xeon	B-General_Concept
Phi	I-General_Concept
"	O
Knights	O
Corner	O
"	O
coprocessors	O
,	O
which	O
implement	O
a	O
subset	O
of	O
x86-64	B-Device
with	O
some	O
vector	O
extensions	O
,	O
are	O
also	O
used	O
,	O
along	O
with	O
x86-64	B-Device
processors	O
,	O
in	O
the	O
Tianhe-2	B-Device
supercomputer	B-Architecture
.	O
</s>
<s>
The	O
following	O
operating	B-General_Concept
systems	I-General_Concept
and	O
releases	O
support	O
the	O
x86-64	B-Device
architecture	O
in	O
long	B-Application
mode	I-Application
.	O
</s>
<s>
Preliminary	O
infrastructure	O
work	O
was	O
started	O
in	O
February	O
2004	O
for	O
a	O
x86-64	B-Device
port	O
.	O
</s>
<s>
and	O
continued	O
during	O
Google	B-Application
Summer	I-Application
of	I-Application
Code	I-Application
2008	O
and	O
SoC	O
2009	O
.	O
</s>
<s>
The	O
first	O
official	O
release	O
to	O
contain	O
x86-64	B-Device
support	O
was	O
version	O
2.4	O
.	O
</s>
<s>
FreeBSD	B-Operating_System
first	O
added	O
x86-64	B-Device
support	O
under	O
the	O
name	O
"	O
amd64	B-Device
"	O
as	O
an	O
experimental	O
architecture	O
in	O
5.1-RELEASE	O
in	O
June	O
2003	O
.	O
</s>
<s>
Since	O
then	O
,	O
FreeBSD	B-Operating_System
has	O
designated	O
it	O
as	O
a	O
Tier1	O
platform	O
.	O
</s>
<s>
The	O
6.0-RELEASE	O
version	O
cleaned	O
up	O
some	O
quirks	O
with	O
running	O
x86	B-Operating_System
executables	B-Application
under	O
amd64	B-Device
,	O
and	O
most	O
drivers	O
work	O
just	O
as	O
they	O
do	O
on	O
the	O
x86	B-Operating_System
architecture	I-Operating_System
.	O
</s>
<s>
Work	O
is	O
currently	O
being	O
done	O
to	O
integrate	O
more	O
fully	O
the	O
x86	B-Operating_System
application	B-Operating_System
binary	I-Operating_System
interface	I-Operating_System
(	O
ABI	O
)	O
,	O
in	O
the	O
same	O
manner	O
as	O
the	O
Linux	B-Operating_System
32-bit	O
ABI	O
compatibility	O
currently	O
works	O
.	O
</s>
<s>
x86-64	B-Device
architecture	O
support	O
was	O
first	O
committed	O
to	O
the	O
NetBSD	B-Device
source	O
tree	O
on	O
June	O
19	O
,	O
2001	O
.	O
</s>
<s>
As	O
of	O
NetBSD2.0	O
,	O
released	O
on	O
December	O
9	O
,	O
2004	O
,	O
NetBSD/amd64	O
is	O
a	O
fully	O
integrated	O
and	O
supported	O
port	O
.	O
</s>
<s>
32-bit	O
code	B-Application
is	O
still	O
supported	O
in	O
64-bit	B-Application
mode	O
,	O
with	O
a	O
netbsd-32	O
kernel	B-Operating_System
compatibility	O
layer	O
for	O
32-bit	O
syscalls	O
.	O
</s>
<s>
The	O
NX	B-General_Concept
bit	I-General_Concept
is	O
used	O
to	O
provide	O
non-executable	O
stack	B-General_Concept
and	O
heap	O
with	O
per-page	O
granularity	O
(	O
segment	O
granularity	O
being	O
used	O
on	O
32-bit	B-Device
x86	I-Device
)	O
.	O
</s>
<s>
OpenBSD	B-Operating_System
has	O
supported	O
AMD64	B-Device
since	O
OpenBSD	B-Operating_System
3.5	O
,	O
released	O
on	O
May	O
1	O
,	O
2004	O
.	O
</s>
<s>
Complete	O
in-tree	O
implementation	O
of	O
AMD64	B-Device
support	O
was	O
achieved	O
prior	O
to	O
the	O
hardware	O
's	O
initial	O
release	O
because	O
AMD	O
had	O
loaned	O
several	O
machines	O
for	O
the	O
project	O
's	O
hackathon	O
that	O
year	O
.	O
</s>
<s>
OpenBSD	B-Operating_System
developers	O
have	O
taken	O
to	O
the	O
platform	O
because	O
of	O
its	O
support	O
for	O
the	O
NX	B-General_Concept
bit	I-General_Concept
,	O
which	O
allowed	O
for	O
an	O
easy	O
implementation	O
of	O
the	O
W^X	O
feature	O
.	O
</s>
<s>
The	O
code	B-Application
for	O
the	O
AMD64	B-Device
port	O
of	O
OpenBSD	B-Operating_System
also	O
runs	O
on	O
Intel	O
64	O
processors	O
which	O
contains	O
cloned	O
use	O
of	O
the	O
AMD64	B-Device
extensions	O
,	O
but	O
since	O
Intel	O
left	O
out	O
the	O
page	B-General_Concept
table	I-General_Concept
NX	B-General_Concept
bit	I-General_Concept
in	O
early	O
Intel	O
64	O
processors	O
,	O
there	O
is	O
no	O
W^X	O
capability	O
on	O
those	O
Intel	O
CPUs	O
;	O
later	O
Intel	O
64	O
processors	O
added	O
the	O
NX	B-General_Concept
bit	I-General_Concept
under	O
the	O
name	O
"	O
XD	B-General_Concept
bit	I-General_Concept
"	O
.	O
</s>
<s>
Symmetric	B-Operating_System
multiprocessing	I-Operating_System
(	O
SMP	O
)	O
works	O
on	O
OpenBSD	B-Operating_System
's	O
AMD64	B-Device
port	O
,	O
starting	O
with	O
release	O
3.6	O
on	O
November	O
1	O
,	O
2004	O
.	O
</s>
<s>
It	O
is	O
possible	O
to	O
enter	O
long	B-Application
mode	I-Application
under	O
DOS	B-Device
without	O
a	O
DOS	B-Device
extender	I-Device
,	O
but	O
the	O
user	O
must	O
return	O
to	O
real	B-Application
mode	I-Application
in	O
order	O
to	O
call	O
BIOS	B-Operating_System
or	O
DOS	B-Device
interrupts	O
.	O
</s>
<s>
It	O
may	O
also	O
be	O
possible	O
to	O
enter	O
long	B-Application
mode	I-Application
with	O
a	O
DOS	B-Device
extender	I-Device
similar	O
to	O
DOS/4GW	B-Application
,	O
but	O
more	O
complex	O
since	O
x86-64	B-Device
lacks	O
virtual	B-Application
8086	I-Application
mode	I-Application
.	O
</s>
<s>
DOS	B-Device
itself	O
is	O
not	O
aware	O
of	O
that	O
,	O
and	O
no	O
benefits	O
should	O
be	O
expected	O
unless	O
running	O
DOS	B-Device
in	O
an	O
emulation	O
with	O
an	O
adequate	O
virtualization	O
driver	O
backend	O
,	O
for	O
example	O
:	O
the	O
mass	O
storage	O
interface	O
.	O
</s>
<s>
Linux	B-Operating_System
was	O
the	O
first	O
operating	B-Operating_System
system	I-Operating_System
kernel	I-Operating_System
to	O
run	O
the	O
x86-64	B-Device
architecture	O
in	O
long	B-Application
mode	I-Application
,	O
starting	O
with	O
the	O
2.4	O
version	O
in	O
2001	O
(	O
preceding	O
the	O
hardware	O
's	O
availability	O
)	O
.	O
</s>
<s>
Linux	B-Operating_System
also	O
provides	O
backward	B-General_Concept
compatibility	I-General_Concept
for	O
running	O
32-bit	O
executables	B-Application
.	O
</s>
<s>
This	O
permits	O
programs	O
to	O
be	O
recompiled	B-Language
into	O
long	B-Application
mode	I-Application
while	O
retaining	O
the	O
use	O
of	O
32-bit	O
programs	O
.	O
</s>
<s>
Current	O
Linux	B-Application
distributions	I-Application
ship	O
with	O
x86-64-native	O
kernels	B-Operating_System
and	O
userlands	O
.	O
</s>
<s>
Some	O
,	O
such	O
as	O
Arch	O
Linux	B-Operating_System
,	O
SUSE	O
,	O
Mandriva	O
,	O
and	O
Debian	O
,	O
allow	O
users	O
to	O
install	O
a	O
set	O
of	O
32-bit	O
components	O
and	O
libraries	O
when	O
installing	O
off	O
a	O
64-bit	B-Application
distribution	O
medium	O
,	O
thus	O
allowing	O
most	O
existing	O
32-bit	O
applications	O
to	O
run	O
alongside	O
the	O
64-bit	B-Device
OS	I-Device
.	O
</s>
<s>
x32	B-Application
ABI	I-Application
(	O
Application	B-Operating_System
Binary	I-Operating_System
Interface	I-Operating_System
)	O
,	O
introduced	O
in	O
Linux	B-Operating_System
3.4	O
,	O
allows	O
programs	O
compiled	B-Language
for	O
the	O
x32	B-Application
ABI	I-Application
to	O
run	O
in	O
the	O
64-bit	B-Application
mode	O
of	O
x86-64	B-Device
while	O
only	O
using	O
32-bit	O
pointers	O
and	O
data	O
fields	O
.	O
</s>
<s>
64-bit	B-Operating_System
Linux	I-Operating_System
allows	O
up	O
to	O
128TB	O
of	O
virtual	O
address	O
space	O
for	O
individual	O
processes	O
,	O
and	O
can	O
address	O
approximately	O
64TB	O
of	O
physical	O
memory	O
,	O
subject	O
to	O
processor	O
and	O
system	O
limitations	O
.	O
</s>
<s>
Mac	O
OS	O
X	O
10.4.7	O
and	O
higher	O
versions	O
of	O
Mac	B-Application
OS	I-Application
X	I-Application
10.4	I-Application
run	O
64-bit	B-Application
command-line	O
tools	O
using	O
the	O
POSIX	O
and	O
math	O
libraries	O
on	O
64-bit	B-Application
Intel-based	O
machines	O
,	O
just	O
as	O
all	O
versions	O
of	O
Mac	B-Application
OS	I-Application
X	I-Application
10.4	I-Application
and	O
10.5	O
run	O
them	O
on	O
64-bit	B-Application
PowerPC	B-Architecture
machines	O
.	O
</s>
<s>
No	O
other	O
libraries	O
or	O
frameworks	O
work	O
with	O
64-bit	B-Application
applications	O
in	O
Mac	B-Application
OS	I-Application
X	I-Application
10.4	I-Application
.	O
</s>
<s>
The	O
kernel	B-Operating_System
,	O
and	O
all	O
kernel	B-Application
extensions	I-Application
,	O
are	O
32-bit	O
only	O
.	O
</s>
<s>
Mac	B-Application
OS	I-Application
X	I-Application
10.5	I-Application
supports	O
64-bit	B-Application
GUI	O
applications	O
using	O
Cocoa	B-Operating_System
,	O
Quartz	B-Operating_System
,	O
OpenGL	B-Application
,	O
and	O
X11	B-Operating_System
on	O
64-bit	B-Application
Intel-based	O
machines	O
,	O
as	O
well	O
as	O
on	O
64-bit	B-Application
PowerPC	B-Architecture
machines	O
.	O
</s>
<s>
All	O
non-GUI	O
libraries	O
and	O
frameworks	O
also	O
support	O
64-bit	B-Application
applications	O
on	O
those	O
platforms	O
.	O
</s>
<s>
The	O
kernel	B-Operating_System
,	O
and	O
all	O
kernel	B-Application
extensions	I-Application
,	O
are	O
32-bit	O
only	O
.	O
</s>
<s>
Mac	B-Device
OS	I-Device
X	I-Device
10.6	I-Device
is	O
the	O
first	O
version	O
of	O
macOS	B-Application
that	O
supports	O
a	O
64-bit	B-Application
kernel	B-Operating_System
.	O
</s>
<s>
However	O
,	O
not	O
all	O
64-bit	B-Device
computers	I-Device
can	O
run	O
the	O
64-bit	B-Application
kernel	B-Operating_System
,	O
and	O
not	O
all	O
64-bit	B-Device
computers	I-Device
that	O
can	O
run	O
the	O
64-bit	B-Application
kernel	B-Operating_System
will	O
do	O
so	O
by	O
default	O
.	O
</s>
<s>
The	O
64-bit	B-Application
kernel	B-Operating_System
,	O
like	O
the	O
32-bit	O
kernel	B-Operating_System
,	O
supports	O
32-bit	O
applications	O
;	O
both	O
kernels	B-Operating_System
also	O
support	O
64-bit	B-Application
applications	O
.	O
</s>
<s>
32-bit	O
applications	O
have	O
a	O
virtual	O
address	O
space	O
limit	O
of	O
4GB	O
under	O
either	O
kernel	B-Operating_System
.	O
</s>
<s>
The	O
64-bit	B-Application
kernel	B-Operating_System
does	O
not	O
support	O
32-bit	O
kernel	B-Application
extensions	I-Application
,	O
and	O
the	O
32-bit	O
kernel	B-Operating_System
does	O
not	O
support	O
64-bit	B-Application
kernel	B-Application
extensions	I-Application
.	O
</s>
<s>
OS	B-Operating_System
X	I-Operating_System
10.8	I-Operating_System
includes	O
only	O
the	O
64-bit	B-Application
kernel	B-Operating_System
,	O
but	O
continues	O
to	O
support	O
32-bit	O
applications	O
;	O
it	O
does	O
not	O
support	O
32-bit	O
kernel	B-Application
extensions	I-Application
,	O
however	O
.	O
</s>
<s>
macOS	B-Device
10.15	I-Device
includes	O
only	O
the	O
64-bit	B-Application
kernel	B-Operating_System
and	O
no	O
longer	O
supports	O
32-bit	O
applications	O
.	O
</s>
<s>
This	O
removal	O
of	O
support	O
has	O
presented	O
a	O
problem	O
for	O
WineHQ	B-Application
(	O
and	O
the	O
commercial	O
version	O
CrossOver	B-Operating_System
)	O
,	O
as	O
it	O
needs	O
to	O
still	O
be	O
able	O
to	O
run	O
32-bit	B-Application
Windows	I-Application
applications	O
.	O
</s>
<s>
The	O
solution	O
,	O
termed	O
wine32on64	O
,	O
was	O
to	O
add	O
thunks	B-Application
that	O
bring	O
the	O
CPU	O
in	O
and	O
out	O
of	O
32-bit	O
compatibility	O
mode	O
in	O
the	O
nominally	O
64-bit	B-Application
application	O
.	O
</s>
<s>
macOS	B-Application
uses	O
the	O
universal	B-Operating_System
binary	I-Operating_System
format	I-Operating_System
to	O
package	O
32	O
-	O
and	O
64-bit	B-Application
versions	O
of	O
application	O
and	O
library	O
code	B-Application
into	O
a	O
single	O
file	O
;	O
the	O
most	O
appropriate	O
version	O
is	O
automatically	O
selected	O
at	O
load	O
time	O
.	O
</s>
<s>
In	O
Mac	B-Device
OS	I-Device
X	I-Device
10.6	I-Device
,	O
the	O
universal	B-Operating_System
binary	I-Operating_System
format	I-Operating_System
is	O
also	O
used	O
for	O
the	O
kernel	B-Operating_System
and	O
for	O
those	O
kernel	B-Application
extensions	I-Application
that	O
support	O
both	O
32-bit	O
and	O
64-bit	B-Application
kernels	B-Operating_System
.	O
</s>
<s>
Solaris	B-Application
10	I-Application
and	O
later	O
releases	O
support	O
the	O
x86-64	B-Device
architecture	O
.	O
</s>
<s>
For	O
Solaris	B-Application
10	I-Application
,	O
just	O
as	O
with	O
the	O
SPARC	B-Architecture
architecture	O
,	O
there	O
is	O
only	O
one	O
operating	B-General_Concept
system	I-General_Concept
image	O
,	O
which	O
contains	O
a	O
32-bit	O
kernel	B-Operating_System
and	O
a	O
64-bit	B-Application
kernel	B-Operating_System
;	O
this	O
is	O
labeled	O
as	O
the	O
"	O
x64/x86	O
"	O
DVD-ROM	O
image	O
.	O
</s>
<s>
The	O
default	O
behavior	O
is	O
to	O
boot	O
a	O
64-bit	B-Application
kernel	B-Operating_System
,	O
allowing	O
both	O
64-bit	B-Application
and	O
existing	O
or	O
new	O
32-bit	O
executables	B-Application
to	O
be	O
run	O
.	O
</s>
<s>
A	O
32-bit	O
kernel	B-Operating_System
can	O
also	O
be	O
manually	O
selected	O
,	O
in	O
which	O
case	O
only	O
32-bit	O
executables	B-Application
will	O
run	O
.	O
</s>
<s>
The	O
isainfo	O
command	O
can	O
be	O
used	O
to	O
determine	O
if	O
a	O
system	O
is	O
running	O
a	O
64-bit	B-Application
kernel	B-Operating_System
.	O
</s>
<s>
For	O
Solaris	B-Application
11	I-Application
,	O
only	O
the	O
64-bit	B-Application
kernel	B-Operating_System
is	O
provided	O
.	O
</s>
<s>
However	O
,	O
the	O
64-bit	B-Application
kernel	B-Operating_System
supports	O
both	O
32	O
-	O
and	O
64-bit	B-Application
executables	B-Application
,	O
libraries	O
,	O
and	O
system	O
calls	O
.	O
</s>
<s>
x64	B-Device
editions	I-Device
of	O
Microsoft	B-Application
Windows	I-Application
client	O
and	O
server	O
—	O
Windows	B-Operating_System
XP	I-Operating_System
Professional	I-Operating_System
x64	I-Operating_System
Edition	I-Operating_System
and	O
Windows	B-Application
Server	I-Application
2003	I-Application
x64	B-Device
Edition	I-Device
—	O
were	O
released	O
in	O
March	O
2005	O
.	O
</s>
<s>
Internally	O
they	O
are	O
actually	O
the	O
same	O
build	O
(	O
5.2.3790.1830	O
SP1	O
)	O
,	O
as	O
they	O
share	O
the	O
same	O
source	O
base	O
and	O
operating	B-General_Concept
system	I-General_Concept
binaries	O
,	O
so	O
even	O
system	O
updates	O
are	O
released	O
in	O
unified	O
packages	O
,	O
much	O
in	O
the	O
manner	O
as	O
Windows	B-Application
2000	O
Professional	O
and	O
Server	O
editions	O
for	O
x86	B-Operating_System
.	O
</s>
<s>
Windows	B-Application
Vista	I-Application
,	O
which	O
also	O
has	O
many	O
different	O
editions	O
,	O
was	O
released	O
in	O
January	O
2007	O
.	O
</s>
<s>
Windows	B-Application
7	O
was	O
released	O
in	O
July	O
2009	O
.	O
</s>
<s>
Windows	B-Device
Server	I-Device
2008	I-Device
R2	I-Device
was	O
sold	O
in	O
only	O
x64	B-Device
and	O
Itanium	B-General_Concept
editions	O
;	O
later	O
versions	O
of	O
Windows	B-Application
Server	O
only	O
offer	O
an	O
x64	B-Device
edition	I-Device
.	O
</s>
<s>
Versions	O
of	O
Windows	B-Application
for	O
x64	B-Device
prior	O
to	O
Windows	B-Device
8.1	I-Device
and	O
Windows	B-Application
Server	O
2012	O
R2	O
offer	O
the	O
following	O
:	O
</s>
<s>
8TB	O
of	O
virtual	O
address	O
space	O
per	O
process	O
,	O
accessible	O
from	O
both	O
user	B-Operating_System
mode	I-Operating_System
and	O
kernel	B-Operating_System
mode	O
,	O
referred	O
to	O
as	O
the	O
user	B-Operating_System
mode	I-Operating_System
address	O
space	O
.	O
</s>
<s>
An	O
x64	B-Device
program	O
can	O
use	O
all	O
of	O
this	O
,	O
subject	O
to	O
backing	O
store	O
limits	O
on	O
the	O
system	O
,	O
and	O
provided	O
it	O
is	O
linked	O
with	O
the	O
"	O
large	O
address	O
aware	O
"	O
option	O
,	O
which	O
is	O
present	O
by	O
default	O
.	O
</s>
<s>
This	O
is	O
a	O
4096-fold	O
increase	O
over	O
the	O
default	O
2GB	O
user-mode	B-Operating_System
virtual	O
address	O
space	O
offered	O
by	O
32-bit	B-Application
Windows	I-Application
.	O
</s>
<s>
8TB	O
of	O
kernel	B-Operating_System
mode	O
virtual	O
address	O
space	O
for	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
As	O
with	O
the	O
user	B-Operating_System
mode	I-Operating_System
address	O
space	O
,	O
this	O
is	O
a	O
4096-fold	O
increase	O
over	O
32-bit	B-Application
Windows	I-Application
versions	O
.	O
</s>
<s>
The	O
increased	O
space	O
primarily	O
benefits	O
the	O
file	O
system	O
cache	O
and	O
kernel	B-Operating_System
mode	O
"	O
heaps	O
"	O
(	O
non-paged	O
pool	O
and	O
paged	O
pool	O
)	O
.	O
</s>
<s>
Windows	B-Application
only	O
uses	O
a	O
total	O
of	O
16TB	O
out	O
of	O
the	O
256TB	O
implemented	O
by	O
the	O
processors	O
because	O
early	O
AMD64	B-Device
processors	O
lacked	O
a	O
CMPXCHG16B	O
instruction	O
.	O
</s>
<s>
Under	O
Windows	B-Device
8.1	I-Device
and	O
Windows	B-Application
Server	O
2012	O
R2	O
,	O
both	O
user	B-Operating_System
mode	I-Operating_System
and	O
kernel	B-Operating_System
mode	O
virtual	O
address	O
spaces	O
have	O
been	O
extended	O
to	O
128TB	O
.	O
</s>
<s>
These	O
versions	O
of	O
Windows	B-Application
will	O
not	O
install	O
on	O
processors	O
that	O
lack	O
the	O
CMPXCHG16B	O
instruction	O
.	O
</s>
<s>
The	O
following	O
additional	O
characteristics	O
apply	O
to	O
all	O
x64	B-Device
versions	O
of	O
Windows	B-Application
:	O
</s>
<s>
Ability	O
to	O
run	O
existing	O
32-bit	O
applications	O
(	O
.exe	O
programs	O
)	O
and	O
dynamic	O
link	O
libraries	O
(	O
.dlls	O
)	O
using	O
WoW64	B-Application
if	O
WoW64	B-Application
is	O
supported	O
on	O
that	O
version	O
.	O
</s>
<s>
Furthermore	O
,	O
a	O
32-bit	O
program	O
,	O
if	O
it	O
was	O
linked	O
with	O
the	O
"	O
large	O
address	O
aware	O
"	O
option	O
,	O
can	O
use	O
up	O
to	O
4GB	O
of	O
virtual	O
address	O
space	O
in	O
64-bit	B-Application
Windows	B-Application
,	O
instead	O
of	O
the	O
default	O
2GB	O
(	O
optional	O
3GB	O
with	O
/3GB	O
boot	O
option	O
and	O
"	O
large	O
address	O
aware	O
"	O
link	O
option	O
)	O
offered	O
by	O
32-bit	B-Application
Windows	I-Application
.	O
</s>
<s>
Unlike	O
the	O
use	O
of	O
the	O
/3GB	O
boot	O
option	O
on	O
x86	B-Operating_System
,	O
this	O
does	O
not	O
reduce	O
the	O
kernel	B-Operating_System
mode	O
virtual	O
address	O
space	O
available	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
32-bit	O
applications	O
can	O
,	O
therefore	O
,	O
benefit	O
from	O
running	O
on	O
x64	B-Device
Windows	B-Application
even	O
if	O
they	O
are	O
not	O
recompiled	B-Language
for	O
x86-64	B-Device
.	O
</s>
<s>
Both	O
32	O
-	O
and	O
64-bit	B-Application
applications	O
,	O
if	O
not	O
linked	O
with	O
"	O
large	O
address	O
aware	O
"	O
,	O
are	O
limited	O
to	O
2GB	O
of	O
virtual	O
address	O
space	O
.	O
</s>
<s>
Ability	O
to	O
use	O
up	O
to	O
128GB	O
(	O
Windows	B-Application
XP/Vista	O
)	O
,	O
192GB	O
(	O
Windows7	O
)	O
,	O
512GB	O
(	O
Windows8	O
)	O
,	O
1TB	O
(	O
Windows	B-Application
Server	I-Application
2003	I-Application
)	O
,	O
2TB	O
(	O
Windows	B-Application
Server	O
2008/Windows	O
10	O
)	O
,	O
4TB	O
(	O
Windows	B-Application
Server	O
2012	O
)	O
,	O
or	O
24TB	O
(	O
Windows	B-Application
Server	O
2016/2019	O
)	O
of	O
physical	O
random	O
access	O
memory	O
(	O
RAM	O
)	O
.	O
</s>
<s>
LLP64	O
data	O
model	O
:	O
in	O
C/C	O
++	O
,	O
"	O
int	O
"	O
and	O
"	O
long	O
"	O
types	O
are	O
32bits	O
wide	O
,	O
"	O
long	O
long	O
"	O
is	O
64bits	B-Device
,	O
while	O
pointers	O
and	O
types	O
derived	O
from	O
pointers	O
are	O
64bits	B-Device
wide	O
.	O
</s>
<s>
Kernel	B-Operating_System
mode	O
device	O
drivers	O
must	O
be	O
64-bit	B-Application
versions	O
;	O
there	O
is	O
no	O
way	O
to	O
run	O
32-bit	O
kernel	B-Operating_System
mode	O
executables	B-Application
within	O
the	O
64-bit	B-Application
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
User	B-Operating_System
mode	I-Operating_System
device	O
drivers	O
can	O
be	O
either	O
32-bit	O
or	O
64-bit	B-Application
.	O
</s>
<s>
16-bit	O
Windows	B-Application
(	O
Win16	O
)	O
and	O
DOS	B-Device
applications	O
will	O
not	O
run	O
on	O
x86-64	B-Device
versions	O
of	O
Windows	B-Application
due	O
to	O
the	O
removal	O
of	O
the	O
virtual	O
DOS	B-Device
machine	O
subsystem	O
(	O
NTVDM	O
)	O
which	O
relied	O
upon	O
the	O
ability	O
to	O
use	O
virtual	B-Application
8086	I-Application
mode	I-Application
.	O
</s>
<s>
Virtual	B-Application
8086	I-Application
mode	I-Application
cannot	O
be	O
entered	O
while	O
running	O
in	O
long	B-Application
mode	I-Application
.	O
</s>
<s>
Full	O
implementation	O
of	O
the	O
NX	B-General_Concept
(	O
No	B-General_Concept
Execute	I-General_Concept
)	O
page	B-Architecture
protection	O
feature	O
.	O
</s>
<s>
This	O
is	O
also	O
implemented	O
on	O
recent	O
32-bit	O
versions	O
of	O
Windows	B-Application
when	O
they	O
are	O
started	O
in	O
PAE	O
mode	O
.	O
</s>
<s>
Instead	O
of	O
FS	O
segment	B-Operating_System
descriptor	I-Operating_System
on	O
x86	B-Operating_System
versions	O
of	O
the	O
Windows	B-Device
NT	I-Device
family	I-Device
,	O
GS	O
segment	B-Operating_System
descriptor	I-Operating_System
is	O
used	O
to	O
point	O
to	O
two	O
operating	B-General_Concept
system	I-General_Concept
defined	O
structures	O
:	O
Thread	O
Information	O
Block	O
(	O
NT_TIB	O
)	O
in	O
user	B-Operating_System
mode	I-Operating_System
and	O
Processor	O
Control	O
Region	O
(	O
KPCR	O
)	O
in	O
kernel	B-Operating_System
mode	O
.	O
</s>
<s>
Thus	O
,	O
for	O
example	O
,	O
in	O
user	B-Operating_System
mode	I-Operating_System
GS:0	O
is	O
the	O
address	O
of	O
the	O
first	O
member	O
of	O
the	O
Thread	O
Information	O
Block	O
.	O
</s>
<s>
Maintaining	O
this	O
convention	O
made	O
the	O
x86-64	B-Device
port	O
easier	O
,	O
but	O
required	O
AMD	O
to	O
retain	O
the	O
function	O
of	O
the	O
FS	B-Device
and	I-Device
GS	I-Device
segments	O
in	O
long	B-Application
mode	I-Application
–	O
even	O
though	O
segmented	B-Device
addressing	I-Device
per	O
se	O
is	O
not	O
really	O
used	O
by	O
any	O
modern	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Early	O
reports	O
claimed	O
that	O
the	O
operating	B-General_Concept
system	I-General_Concept
scheduler	O
would	O
not	O
save	O
and	O
restore	O
the	O
x87	B-Application
FPU	I-Application
machine	O
state	O
across	O
thread	O
context	O
switches	O
.	O
</s>
<s>
Observed	O
behavior	O
shows	O
that	O
this	O
is	O
not	O
the	O
case	O
:	O
the	O
x87	B-Application
state	O
is	O
saved	O
and	O
restored	O
,	O
except	O
for	O
kernel	B-Operating_System
mode-only	O
threads	O
(	O
a	O
limitation	O
that	O
exists	O
in	O
the	O
32-bit	O
version	O
as	O
well	O
)	O
.	O
</s>
<s>
The	O
most	O
recent	O
documentation	O
available	O
from	O
Microsoft	O
states	O
that	O
the	O
x87/MMX/3DNow	O
!	O
</s>
<s>
instructions	O
may	O
be	O
used	O
in	O
long	B-Application
mode	I-Application
,	O
but	O
that	O
they	O
are	O
deprecated	O
and	O
may	O
cause	O
compatibility	O
problems	O
in	O
the	O
future	O
.	O
</s>
<s>
(	O
3DNow	B-General_Concept
!	I-General_Concept
</s>
<s>
is	O
no	O
longer	O
available	O
on	O
AMD	O
processors	O
,	O
with	O
the	O
exception	O
of	O
the	O
PREFETCH	O
and	O
PREFETCHW	O
instructions	O
,	O
which	O
are	O
also	O
supported	O
on	O
Intel	O
processors	O
as	O
of	O
Broadwell	B-General_Concept
.	O
)	O
</s>
<s>
Some	O
components	O
like	O
Jet	B-Application
Database	I-Application
Engine	I-Application
and	O
Data	B-Library
Access	I-Library
Objects	I-Library
will	O
not	O
be	O
ported	O
to	O
64-bit	B-Device
architectures	I-Device
such	O
as	O
x86-64	B-Device
and	O
IA-64	B-General_Concept
.	O
</s>
<s>
Microsoft	B-Application
Visual	I-Application
Studio	I-Application
can	O
compile	B-Language
native	B-Language
applications	I-Language
to	O
target	O
either	O
the	O
x86-64	B-Device
architecture	O
,	O
which	O
can	O
run	O
only	O
on	O
64-bit	B-Application
Microsoft	B-Application
Windows	I-Application
,	O
or	O
the	O
IA-32	B-Device
architecture	O
,	O
which	O
can	O
run	O
as	O
a	O
32-bit	O
application	O
on	O
32-bit	O
Microsoft	B-Application
Windows	I-Application
or	O
64-bit	B-Application
Microsoft	B-Application
Windows	I-Application
in	O
WoW64	B-Application
emulation	O
mode	O
.	O
</s>
<s>
Managed	O
applications	O
can	O
be	O
compiled	B-Language
either	O
in	O
IA-32	B-Device
,	O
x86-64	B-Device
or	O
AnyCPU	O
modes	O
.	O
</s>
<s>
Software	O
created	O
in	O
the	O
first	O
two	O
modes	O
behave	O
like	O
their	O
IA-32	B-Device
or	O
x86-64	B-Device
native	B-Language
code	I-Language
counterparts	O
respectively	O
;	O
When	O
using	O
the	O
AnyCPU	O
mode	O
,	O
however	O
,	O
applications	O
in	O
32-bit	O
versions	O
of	O
Microsoft	B-Application
Windows	I-Application
run	O
as	O
32-bit	O
applications	O
,	O
while	O
they	O
run	O
as	O
a	O
64-bit	B-Application
application	O
in	O
64-bit	B-Application
editions	O
of	O
Microsoft	B-Application
Windows	I-Application
.	O
</s>
<s>
Both	O
the	B-Operating_System
PlayStation	I-Operating_System
4	I-Operating_System
and	O
Xbox	B-Device
One	I-Device
,	O
and	O
all	O
variants	O
of	O
those	O
consoles	O
,	O
incorporate	O
AMD	O
x86-64	B-Device
processors	O
,	O
based	O
on	O
the	O
Jaguar	O
microarchitecture	B-General_Concept
.	O
</s>
<s>
Firmware	O
and	O
games	O
are	O
written	O
in	O
x86-64	B-Device
code	B-Application
;	O
no	O
legacy	O
x86	B-Operating_System
code	B-Application
is	O
involved	O
.	O
</s>
<s>
The	O
current	O
generation	O
,	O
the	O
PlayStation	B-Device
5	I-Device
and	O
the	O
Xbox	B-Device
Series	I-Device
X	I-Device
and	I-Device
Series	I-Device
S	I-Device
respectively	O
,	O
also	O
incorporate	O
AMD	O
x86-64	B-Device
processors	O
,	O
based	O
on	O
the	O
Zen	O
2	O
microarchitecture	B-General_Concept
.	O
</s>
<s>
Although	O
considered	O
a	O
PC	O
,	O
the	O
Steam	B-Device
Deck	I-Device
uses	O
a	O
custom	O
AMD	O
x86-64	B-Device
accelerated	B-Architecture
processing	I-Architecture
unit	I-Architecture
(	O
APU	O
)	O
,	O
based	O
on	O
the	O
Zen	O
2	O
microarchitecture	B-General_Concept
.	O
</s>
<s>
Since	O
AMD64	B-Device
and	O
Intel	O
64	O
are	O
substantially	O
similar	O
,	O
many	O
software	O
and	O
hardware	O
products	O
use	O
one	O
vendor-neutral	O
term	O
to	O
indicate	O
their	O
compatibility	O
with	O
both	O
implementations	O
.	O
</s>
<s>
AMD	O
's	O
original	O
designation	O
for	O
this	O
processor	O
architecture	O
,	O
"	O
x86-64	B-Device
"	O
,	O
is	O
still	O
sometimes	O
used	O
for	O
this	O
purpose	O
,	O
as	O
is	O
the	O
variant	O
"	O
x86_64	O
"	O
.	O
</s>
<s>
Other	O
companies	O
,	O
such	O
as	O
Microsoft	O
and	O
Sun	O
Microsystems/Oracle	O
Corporation	O
,	O
use	O
the	O
contraction	O
"	O
x64	B-Device
"	O
in	O
marketing	O
material	O
.	O
</s>
<s>
The	O
term	O
IA-64	B-General_Concept
refers	O
to	O
the	O
Itanium	B-General_Concept
processor	O
,	O
and	O
should	O
not	O
be	O
confused	O
with	O
x86-64	B-Device
,	O
as	O
it	O
is	O
a	O
completely	O
different	O
instruction	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
Many	O
operating	B-General_Concept
systems	I-General_Concept
and	O
products	O
,	O
especially	O
those	O
that	O
introduced	O
x86-64	B-Device
support	O
prior	O
to	O
Intel	O
's	O
entry	O
into	O
the	O
market	O
,	O
use	O
the	O
term	O
"	O
AMD64	B-Device
"	O
or	O
"	O
amd64	B-Device
"	O
to	O
refer	O
to	O
both	O
AMD64	B-Device
and	O
Intel	O
64	O
.	O
</s>
<s>
Most	O
BSD	B-Operating_System
systems	O
such	O
as	O
FreeBSD	B-Operating_System
,	O
MidnightBSD	B-Application
,	O
NetBSD	B-Device
and	O
OpenBSD	B-Operating_System
refer	O
to	O
both	O
AMD64	B-Device
and	O
Intel	O
64	O
under	O
the	O
architecture	O
name	O
"	O
amd64	B-Device
"	O
.	O
</s>
<s>
Some	O
Linux	B-Application
distributions	I-Application
such	O
as	O
Debian	O
,	O
Ubuntu	B-Operating_System
,	O
Gentoo	B-Application
Linux	I-Application
refer	O
to	O
both	O
AMD64	B-Device
and	O
Intel	O
64	O
under	O
the	O
architecture	O
name	O
"	O
amd64	B-Device
"	O
.	O
</s>
<s>
Microsoft	B-Application
Windows	I-Application
's	O
x64	B-Device
versions	O
use	O
the	O
AMD64	B-Device
moniker	O
internally	O
to	O
designate	O
various	O
components	O
which	O
use	O
or	O
are	O
compatible	O
with	O
this	O
architecture	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
environment	O
variable	O
PROCESSOR_ARCHITECTURE	O
is	O
assigned	O
the	O
value	O
"	O
AMD64	B-Device
"	O
as	O
opposed	O
to	O
"	O
x86	B-Operating_System
"	O
in	O
32-bit	O
versions	O
,	O
and	O
the	O
system	O
directory	O
on	O
a	O
Windows	B-Application
x64	B-Device
Edition	I-Device
installation	O
CD-ROM	O
is	O
named	O
"	O
AMD64	B-Device
"	O
,	O
in	O
contrast	O
to	O
"	O
i386	O
"	O
in	O
32-bit	O
versions	O
.	O
</s>
<s>
Sun	O
's	O
Solaris	B-Application
's	O
isalist	O
command	O
identifies	O
both	O
AMD64	B-Device
-	O
and	O
Intel	O
64-based	O
systems	O
as	O
"	O
amd64	B-Device
"	O
.	O
</s>
<s>
Java	B-Language
Development	I-Language
Kit	I-Language
(	O
JDK	B-Language
)	O
:	O
the	O
name	O
"	O
amd64	B-Device
"	O
is	O
used	O
in	O
directory	O
names	O
containing	O
x86-64	B-Device
files	O
.	O
</s>
<s>
The	O
Linux	B-Operating_System
kernel	I-Operating_System
and	O
the	O
GNU	B-Application
Compiler	I-Application
Collection	I-Application
refers	O
to	O
64-bit	B-Device
architecture	I-Device
as	O
"	O
x86_64	O
"	O
.	O
</s>
<s>
Some	O
Linux	B-Application
distributions	I-Application
,	O
such	O
as	O
Fedora	O
,	O
openSUSE	B-Operating_System
,	O
Arch	O
Linux	B-Operating_System
,	O
Gentoo	B-Application
Linux	I-Application
refer	O
to	O
this	O
64-bit	B-Device
architecture	I-Device
as	O
"	O
x86_64	O
"	O
.	O
</s>
<s>
Apple	O
macOS	B-Application
refers	O
to	O
64-bit	B-Device
architecture	I-Device
as	O
"	O
x86-64	B-Device
"	O
or	O
"	O
x86_64	O
"	O
,	O
as	O
seen	O
in	O
the	O
Terminal	O
command	O
arch	O
and	O
in	O
their	O
developer	O
documentation	O
.	O
</s>
<s>
Breaking	O
with	O
most	O
other	O
BSD	B-Operating_System
systems	O
,	O
DragonFly	B-Application
BSD	I-Application
refers	O
to	O
64-bit	B-Device
architecture	I-Device
as	O
"	O
x86_64	O
"	O
.	O
</s>
<s>
Haiku	B-Language
refers	O
to	O
64-bit	B-Device
architecture	I-Device
as	O
"	O
x86_64	O
"	O
.	O
</s>
<s>
x86-64/AMD64	O
was	O
solely	O
developed	O
by	O
AMD	O
.	O
</s>
<s>
AMD	O
holds	O
patents	O
on	O
techniques	O
used	O
in	O
AMD64	B-Device
;	O
those	O
patents	O
must	O
be	O
licensed	O
from	O
AMD	O
in	O
order	O
to	O
implement	O
AMD64	B-Device
.	O
</s>
<s>
Intel	O
entered	O
into	O
a	O
cross-licensing	O
agreement	O
with	O
AMD	O
,	O
licensing	O
to	O
AMD	O
their	O
patents	O
on	O
existing	O
x86	B-Operating_System
techniques	O
,	O
and	O
licensing	O
from	O
AMD	O
their	O
patents	O
on	O
techniques	O
used	O
in	O
x86-64	B-Device
.	O
</s>
