<s>
In	O
computer	B-General_Concept
architecture	I-General_Concept
,	O
64-bit	B-Device
integers	O
,	O
memory	O
addresses	O
,	O
or	O
other	O
data	B-General_Concept
units	O
are	O
those	O
that	O
are	O
64	B-Device
bits	I-Device
wide	O
.	O
</s>
<s>
Also	O
,	O
64-bit	B-Device
CPUs	I-Device
and	O
ALUs	B-General_Concept
are	O
those	O
that	O
are	O
based	O
on	O
processor	B-General_Concept
registers	I-General_Concept
,	O
address	O
buses	O
,	O
or	O
data	B-General_Concept
buses	I-General_Concept
of	O
that	O
size	O
.	O
</s>
<s>
A	O
computer	O
that	O
uses	O
such	O
a	O
processor	O
is	O
a	O
64-bit	B-Device
computer	I-Device
.	O
</s>
<s>
From	O
the	O
software	O
perspective	O
,	O
64-bit	B-Device
computing	I-Device
means	O
the	O
use	O
of	O
machine	B-Language
code	I-Language
with	O
64-bit	B-Device
virtual	B-Architecture
memory	I-Architecture
addresses	O
.	O
</s>
<s>
However	O
,	O
not	O
all	O
64-bit	B-Device
instruction	B-General_Concept
sets	I-General_Concept
support	O
full	O
64-bit	B-Device
virtual	B-Architecture
memory	I-Architecture
addresses	O
;	O
x86-64	B-Device
and	O
ARMv8	O
,	O
for	O
example	O
,	O
support	O
only	O
48	O
bits	O
of	O
virtual	O
address	O
,	O
with	O
the	O
remaining	O
16	O
bits	O
of	O
the	O
virtual	O
address	O
required	O
to	O
be	O
all	O
0	O
's	O
or	O
all	O
1	O
's	O
,	O
and	O
several	O
64-bit	B-Device
instruction	B-General_Concept
sets	I-General_Concept
support	O
fewer	O
than	O
64	B-Device
bits	I-Device
of	O
physical	O
memory	B-General_Concept
address	I-General_Concept
.	O
</s>
<s>
The	O
term	O
64-bit	B-Device
also	O
describes	O
a	O
generation	O
of	O
computers	O
in	O
which	O
64-bit	B-Device
processors	I-Device
are	O
the	O
norm	O
.	O
</s>
<s>
64	B-Device
bits	I-Device
is	O
a	O
word	O
size	O
that	O
defines	O
certain	O
classes	O
of	O
computer	B-General_Concept
architecture	I-General_Concept
,	O
buses	O
,	O
memory	O
,	O
and	O
CPUs	B-General_Concept
and	O
,	O
by	O
extension	O
,	O
the	O
software	O
that	O
runs	O
on	O
them	O
.	O
</s>
<s>
64-bit	B-Device
CPUs	I-Device
have	O
been	O
used	O
in	O
supercomputers	B-Architecture
since	O
the	O
1970s	O
(	O
Cray-1	B-Device
,	O
1975	O
)	O
and	O
in	O
reduced	B-Architecture
instruction	I-Architecture
set	I-Architecture
computers	I-Architecture
(	O
RISC	B-Architecture
)	O
based	O
workstations	B-Device
and	O
servers	O
since	O
the	O
early	O
1990s	O
.	O
</s>
<s>
In	O
2003	O
,	O
64-bit	B-Device
CPUs	I-Device
were	O
introduced	O
to	O
the	O
mainstream	O
PC	B-Device
market	O
in	O
the	O
form	O
of	O
x86-64	B-Device
processors	O
and	O
the	O
PowerPC	B-General_Concept
G5	I-General_Concept
.	O
</s>
<s>
A	O
64-bit	B-Device
register	O
can	O
hold	O
any	O
of	O
264	O
(	O
over	O
18	O
quintillion	O
or	O
1.8	O
×1019	O
)	O
different	O
values	O
.	O
</s>
<s>
The	O
range	O
of	O
integer	O
values	O
that	O
can	O
be	O
stored	O
in	O
64	B-Device
bits	I-Device
depends	O
on	O
the	O
integer	O
representation	O
used	O
.	O
</s>
<s>
With	O
the	O
two	O
most	O
common	O
representations	O
,	O
the	O
range	O
is	O
0	O
through	O
18,446,744,073,709,551,615	O
(	O
264	O
−	O
1	O
)	O
for	O
representation	O
as	O
an	O
(	O
unsigned	B-Algorithm
)	O
binary	O
number	O
,	O
and	O
−	O
9,223,372,036,854,775,808	O
( −263	O
)	O
through	O
9,223,372,036,854,775,807	O
(	O
263	O
−	O
1	O
)	O
for	O
representation	O
as	O
two	B-General_Concept
's	I-General_Concept
complement	I-General_Concept
.	O
</s>
<s>
Hence	O
,	O
a	O
processor	O
with	O
64-bit	B-Device
memory	O
addresses	O
can	O
directly	O
access	O
264	O
bytes	O
(	O
16	O
exbibytes	O
or	O
EiB	O
)	O
of	O
byte-addressable	B-General_Concept
memory	O
.	O
</s>
<s>
With	O
no	O
further	O
qualification	O
,	O
a	O
64-bit	B-Device
computer	I-Device
architecture	O
generally	O
has	O
integer	O
and	O
addressing	O
registers	B-General_Concept
that	O
are	O
64	B-Device
bits	I-Device
wide	O
,	O
allowing	O
direct	O
support	O
for	O
64-bit	B-Device
data	B-General_Concept
types	O
and	O
addresses	O
.	O
</s>
<s>
However	O
,	O
a	O
CPU	O
might	O
have	O
external	O
data	B-General_Concept
buses	I-General_Concept
or	O
address	O
buses	O
with	O
different	O
sizes	O
from	O
the	O
registers	B-General_Concept
,	O
even	O
larger	O
(	O
the	O
32-bit	O
Pentium	B-General_Concept
had	O
a	O
64-bit	B-Device
data	B-General_Concept
bus	I-General_Concept
,	O
for	O
instance	O
)	O
.	O
</s>
<s>
Processor	B-General_Concept
registers	I-General_Concept
are	O
typically	O
divided	O
into	O
several	O
groups	O
:	O
integer	O
,	O
floating-point	B-Algorithm
,	O
single	B-Device
instruction	I-Device
,	I-Device
multiple	I-Device
data	I-Device
(	O
SIMD	B-Device
)	O
,	O
control	O
,	O
and	O
often	O
special	O
registers	B-General_Concept
for	O
address	O
arithmetic	O
which	O
may	O
have	O
various	O
uses	O
and	O
names	O
such	O
as	O
address	O
,	O
index	O
,	O
or	O
base	O
registers	B-General_Concept
.	O
</s>
<s>
However	O
,	O
in	O
modern	O
designs	O
,	O
these	O
functions	O
are	O
often	O
performed	O
by	O
more	O
general	O
purpose	O
integer	O
registers	B-General_Concept
.	O
</s>
<s>
In	O
most	O
processors	O
,	O
only	O
integer	O
or	O
address-registers	O
can	O
be	O
used	O
to	O
address	O
data	B-General_Concept
in	O
memory	O
;	O
the	O
other	O
types	O
of	O
registers	B-General_Concept
cannot	O
.	O
</s>
<s>
The	O
size	O
of	O
these	O
registers	B-General_Concept
therefore	O
normally	O
limits	O
the	O
amount	O
of	O
directly	O
addressable	O
memory	O
,	O
even	O
if	O
there	O
are	O
registers	B-General_Concept
,	O
such	O
as	O
floating-point	B-Algorithm
registers	B-General_Concept
,	O
that	O
are	O
wider	O
.	O
</s>
<s>
Most	O
high	O
performance	O
32-bit	O
and	O
64-bit	B-Device
processors	I-Device
(	O
some	O
notable	O
exceptions	O
are	O
older	O
or	O
embedded	O
ARM	B-Architecture
architecture	I-Architecture
(	O
ARM	O
)	O
and	O
32-bit	O
MIPS	B-Device
architecture	I-Device
(	O
MIPS	O
)	O
CPUs	B-General_Concept
)	O
have	O
integrated	O
floating	B-Algorithm
point	I-Algorithm
hardware	O
,	O
which	O
is	O
often	O
,	O
but	O
not	O
always	O
,	O
based	O
on	O
64-bit	B-Device
units	O
of	O
data	B-General_Concept
.	O
</s>
<s>
For	O
example	O
,	O
although	O
the	O
x86/x87	O
architecture	O
has	O
instructions	O
able	O
to	O
load	O
and	O
store	O
64-bit	B-Device
(	O
and	O
32-bit	O
)	O
floating-point	B-Algorithm
values	O
in	O
memory	O
,	O
the	O
internal	O
floating	B-Algorithm
point	I-Algorithm
data	B-General_Concept
and	O
register	O
format	O
is	O
80	O
bits	O
wide	O
,	O
while	O
the	O
general-purpose	O
registers	B-General_Concept
are	O
32	O
bits	O
wide	O
.	O
</s>
<s>
In	O
contrast	O
,	O
the	O
64-bit	B-Device
Alpha	B-Device
family	O
uses	O
a	O
64-bit	B-Device
floating-point	B-Algorithm
data	B-General_Concept
and	O
register	O
format	O
,	O
and	O
64-bit	B-Device
integer	O
registers	B-General_Concept
.	O
</s>
<s>
Many	O
computer	O
instruction	B-General_Concept
sets	I-General_Concept
are	O
designed	O
so	O
that	O
a	O
single	O
integer	O
register	O
can	O
store	O
the	O
memory	B-General_Concept
address	I-General_Concept
to	O
any	O
location	O
in	O
the	O
computer	O
's	O
physical	O
or	O
virtual	B-Architecture
memory	I-Architecture
.	O
</s>
<s>
Therefore	O
,	O
the	O
total	O
number	O
of	O
addresses	O
to	O
memory	O
is	O
often	O
determined	O
by	O
the	O
width	O
of	O
these	O
registers	B-General_Concept
.	O
</s>
<s>
The	O
IBM	B-Application
System/360	I-Application
of	O
the	O
1960s	O
was	O
an	O
early	O
32-bit	O
computer	O
;	O
it	O
had	O
32-bit	O
integer	O
registers	B-General_Concept
,	O
although	O
it	O
only	O
used	O
the	O
low	O
order	O
24	O
bits	O
of	O
a	O
word	O
for	O
addresses	O
,	O
resulting	O
in	O
a	O
16MiB	O
(	O
)	O
address	B-General_Concept
space	I-General_Concept
.	O
</s>
<s>
32-bit	O
superminicomputers	B-Device
,	O
such	O
as	O
the	O
DEC	B-Device
VAX	I-Device
,	O
became	O
common	O
in	O
the	O
1970s	O
,	O
and	O
32-bit	O
microprocessors	O
,	O
such	O
as	O
the	O
Motorola	B-Device
68000	I-Device
family	I-Device
and	O
the	O
32-bit	B-Device
members	I-Device
of	I-Device
the	I-Device
x86	I-Device
family	I-Device
starting	O
with	O
the	O
Intel	B-General_Concept
80386	I-General_Concept
,	O
appeared	O
in	O
the	O
mid-1980s	O
,	O
making	O
32	O
bits	O
something	O
of	O
a	O
de	O
facto	O
consensus	O
as	O
a	O
convenient	O
register	O
size	O
.	O
</s>
<s>
A	O
32-bit	O
address	B-General_Concept
register	I-General_Concept
meant	O
that	O
232	O
addresses	O
,	O
or	O
4GiB	O
of	O
random-access	B-Architecture
memory	I-Architecture
(	O
RAM	B-Architecture
)	O
,	O
could	O
be	O
referenced	O
.	O
</s>
<s>
Some	O
supercomputer	B-Architecture
architectures	O
of	O
the	O
1970s	O
and	O
1980s	O
,	O
such	O
as	O
the	O
Cray-1	B-Device
,	O
used	O
registers	B-General_Concept
up	O
to	O
64	B-Device
bits	I-Device
wide	O
,	O
and	O
supported	O
64-bit	B-Device
integer	O
arithmetic	O
,	O
although	O
they	O
did	O
not	O
support	O
64-bit	B-Device
addressing	O
.	O
</s>
<s>
In	O
the	O
mid-1980s	O
,	O
Intel	B-General_Concept
i860	I-General_Concept
development	O
began	O
culminating	O
in	O
a	O
(	O
too	O
late	O
for	O
Windows	O
NT	O
)	O
1989	O
release	O
;	O
the	O
i860	O
had	O
32-bit	O
integer	O
registers	B-General_Concept
and	O
32-bit	O
addressing	O
,	O
so	O
it	O
was	O
not	O
a	O
fully	O
64-bit	B-Device
processor	I-Device
,	O
although	O
its	O
graphics	O
unit	O
supported	O
64-bit	B-Device
integer	O
arithmetic	O
.	O
</s>
<s>
However	O
,	O
32	O
bits	O
remained	O
the	O
norm	O
until	O
the	O
early	O
1990s	O
,	O
when	O
the	O
continual	O
reductions	O
in	O
the	O
cost	O
of	O
memory	O
led	O
to	O
installations	O
with	O
amounts	O
of	O
RAM	B-Architecture
approaching	O
4GiB	O
,	O
and	O
the	O
use	O
of	O
virtual	B-Architecture
memory	I-Architecture
spaces	O
exceeding	O
the	O
4GiB	O
ceiling	O
became	O
desirable	O
for	O
handling	O
certain	O
types	O
of	O
problems	O
.	O
</s>
<s>
In	O
response	O
,	O
MIPS	O
and	O
DEC	O
developed	O
64-bit	B-Device
microprocessor	O
architectures	O
,	O
initially	O
for	O
high-end	O
workstation	B-Device
and	O
server	B-Application
machines	O
.	O
</s>
<s>
By	O
the	O
mid-1990s	O
,	O
HAL	O
Computer	O
Systems	O
,	O
Sun	O
Microsystems	O
,	O
IBM	O
,	O
Silicon	O
Graphics	O
,	O
and	O
Hewlett-Packard	O
had	O
developed	O
64-bit	B-Device
architectures	I-Device
for	O
their	O
workstation	B-Device
and	O
server	B-Application
systems	O
.	O
</s>
<s>
A	O
notable	O
exception	O
to	O
this	O
trend	O
were	O
mainframes	B-Device
from	O
IBM	O
,	O
which	O
then	O
used	O
32-bit	O
data	B-General_Concept
and	O
31-bit	O
address	O
sizes	O
;	O
the	O
IBM	B-Device
mainframes	I-Device
did	O
not	O
include	O
64-bit	B-Device
processors	I-Device
until	O
2000	O
.	O
</s>
<s>
During	O
the	O
1990s	O
,	O
several	O
low-cost	O
64-bit	B-Device
microprocessors	O
were	O
used	O
in	O
consumer	O
electronics	O
and	O
embedded	O
applications	O
.	O
</s>
<s>
Notably	O
,	O
the	O
Nintendo	B-Operating_System
64	I-Operating_System
and	O
the	O
PlayStation	B-Device
2	I-Device
had	O
64-bit	B-Device
microprocessors	O
before	O
their	O
introduction	O
in	O
personal	B-Device
computers	I-Device
.	O
</s>
<s>
High-end	O
printers	O
,	O
network	O
equipment	O
,	O
and	O
industrial	O
computers	O
,	O
also	O
used	O
64-bit	B-Device
microprocessors	O
,	O
such	O
as	O
the	O
Quantum	O
Effect	O
Devices	O
R5000	B-General_Concept
.	O
</s>
<s>
64-bit	B-Device
computing	I-Device
started	O
to	O
trickle	O
down	O
to	O
the	O
personal	B-Device
computer	I-Device
desktop	O
from	O
2003	O
onward	O
,	O
when	O
some	O
models	O
in	O
Apple	O
's	O
Macintosh	O
lines	O
switched	O
to	O
PowerPC	B-General_Concept
970	I-General_Concept
processors	O
(	O
termed	O
G5	O
by	O
Apple	O
)	O
,	O
and	O
Advanced	O
Micro	O
Devices	O
(	O
AMD	O
)	O
released	O
its	O
first	O
64-bit	O
x86-64	O
processor	O
.	O
</s>
<s>
1961	O
IBM	O
delivers	O
the	O
IBM	B-Device
7030	I-Device
Stretch	I-Device
supercomputer	B-Architecture
,	O
which	O
uses	O
64-bit	B-Device
data	B-General_Concept
words	O
and	O
32	O
-	O
or	O
64-bit	B-Device
instruction	O
words	O
.	O
</s>
<s>
1974	O
Control	O
Data	B-General_Concept
Corporation	O
launches	O
the	O
CDC	B-Device
Star-100	I-Device
vector	O
supercomputer	B-Architecture
,	O
which	O
uses	O
a	O
64-bit	B-Device
word	O
architecture	O
(	O
prior	O
CDC	O
systems	O
were	O
based	O
on	O
a	O
60-bit	O
architecture	O
)	O
.	O
</s>
<s>
International	O
Computers	O
Limited	O
launches	O
the	O
ICL	B-Device
2900	I-Device
Series	I-Device
with	O
32-bit	O
,	O
64-bit	B-Device
,	O
and	O
128-bit	O
two	B-General_Concept
's	I-General_Concept
complement	I-General_Concept
integers	O
;	O
64-bit	B-Device
and	O
128-bit	O
floating	B-Algorithm
point	I-Algorithm
;	O
32-bit	O
,	O
64-bit	B-Device
,	O
and	O
128-bit	O
packed	O
decimal	O
and	O
a	O
128-bit	O
accumulator	O
register	O
.	O
</s>
<s>
The	O
latest	O
is	O
the	O
Fujitsu	O
Supernova	O
,	O
which	O
emulates	B-Application
the	O
original	O
environment	O
on	O
64-bit	B-Device
Intel	O
processors	O
.	O
</s>
<s>
1976	O
Cray	O
Research	O
delivers	O
the	O
first	O
Cray-1	B-Device
supercomputer	B-Architecture
,	O
which	O
is	O
based	O
on	O
a	O
64-bit	B-Device
word	O
architecture	O
and	O
will	O
form	O
the	O
basis	O
for	O
later	O
Cray	O
vector	O
supercomputers	B-Architecture
.	O
</s>
<s>
1983	O
Elxsi	O
launches	O
the	O
Elxsi	O
6400	O
parallel	O
minisupercomputer	B-Device
.	O
</s>
<s>
The	O
Elxsi	O
architecture	O
has	O
64-bit	B-Device
data	B-General_Concept
registers	B-General_Concept
but	O
a	O
32-bit	O
address	B-General_Concept
space	I-General_Concept
.	O
</s>
<s>
1989	O
Intel	O
introduces	O
the	O
Intel	B-General_Concept
i860	I-General_Concept
reduced	B-Architecture
instruction	I-Architecture
set	I-Architecture
computer	I-Architecture
(	O
RISC	B-Architecture
)	O
processor	O
.	O
</s>
<s>
Marketed	O
as	O
a	O
"	O
64-Bit	B-Device
Microprocessor	O
"	O
,	O
it	O
had	O
essentially	O
a	O
32-bit	O
architecture	O
,	O
enhanced	O
with	O
a	O
3D	O
graphics	O
unit	O
capable	O
of	O
64-bit	B-Device
integer	O
operations	O
.	O
</s>
<s>
1993	O
Atari	O
introduces	O
the	O
Atari	B-Device
Jaguar	I-Device
video	B-Device
game	I-Device
console	I-Device
,	O
which	O
includes	O
some	O
64-bit	B-Device
wide	O
data	B-General_Concept
paths	O
in	O
its	O
architecture	O
.	O
</s>
<s>
1991	O
MIPS	O
Computer	O
Systems	O
produces	O
the	O
first	O
64-bit	B-Device
microprocessor	O
,	O
the	O
R4000	B-General_Concept
,	O
which	O
implements	O
the	O
MIPS	O
III	O
architecture	O
,	O
the	O
third	O
revision	O
of	O
its	O
MIPS	B-Device
architecture	I-Device
.	O
</s>
<s>
The	O
CPU	O
is	O
used	O
in	O
SGI	O
graphics	O
workstations	B-Device
starting	O
with	O
the	O
IRIS	B-Device
Crimson	I-Device
.	O
</s>
<s>
Kendall	O
Square	O
Research	O
deliver	O
their	O
first	O
KSR1	O
supercomputer	B-Architecture
,	O
based	O
on	O
a	O
proprietary	O
64-bit	B-Device
RISC	B-Architecture
processor	I-Architecture
architecture	O
running	O
OSF/1	O
.	O
</s>
<s>
1992	O
Digital	O
Equipment	O
Corporation	O
(	O
DEC	O
)	O
introduces	O
the	O
pure	O
64-bit	B-Device
Alpha	B-Device
architecture	O
which	O
was	O
born	O
from	O
the	O
PRISM	B-Architecture
project	O
.	O
</s>
<s>
1994	O
Intel	O
announces	O
plans	O
for	O
the	O
64-bit	B-Device
IA-64	B-General_Concept
architecture	O
(	O
jointly	O
developed	O
with	O
Hewlett-Packard	O
)	O
as	O
a	O
successor	O
to	O
its	O
32-bit	O
IA-32	B-Device
processors	O
.	O
</s>
<s>
1995	O
Sun	O
launches	O
a	O
64-bit	B-Device
SPARC	B-Architecture
processor	O
,	O
the	O
UltraSPARC	B-General_Concept
.	O
</s>
<s>
Fujitsu-owned	O
HAL	O
Computer	O
Systems	O
launches	O
workstations	B-Device
based	O
on	O
a	O
64-bit	B-Device
CPU	I-Device
,	O
HAL	O
's	O
independently	O
designed	O
first-generation	O
SPARC64	B-General_Concept
.	O
</s>
<s>
IBM	O
releases	O
the	O
A10	O
and	O
A30	O
microprocessors	O
,	O
the	O
first	O
64-bit	B-Device
PowerPC	B-Architecture
AS	O
processors	O
.	O
</s>
<s>
IBM	O
also	O
releases	O
a	O
64-bit	B-Device
AS/400	B-Device
system	O
upgrade	O
,	O
which	O
can	O
convert	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
database	O
and	O
applications	O
.	O
</s>
<s>
1996	O
Nintendo	O
introduces	O
the	O
Nintendo	B-Operating_System
64	I-Operating_System
video	B-Device
game	I-Device
console	I-Device
,	O
built	O
around	O
a	O
low-cost	O
variant	O
of	O
the	O
MIPS	B-General_Concept
R4000	I-General_Concept
.	O
</s>
<s>
HP	O
releases	O
the	O
first	O
implementation	O
of	O
its	O
64-bit	B-Device
PA-RISC	B-Device
2.0	I-Device
architecture	O
,	O
the	O
PA-8000	B-General_Concept
.	O
</s>
<s>
1998	O
IBM	O
releases	O
the	O
POWER3	B-General_Concept
line	O
of	O
full-64-bit	O
PowerPC/POWER	O
processors	O
.	O
</s>
<s>
1999	O
Intel	O
releases	O
the	O
instruction	B-General_Concept
set	I-General_Concept
for	O
the	O
IA-64	B-General_Concept
architecture	O
.	O
</s>
<s>
AMD	O
publicly	O
discloses	O
its	O
set	O
of	O
64-bit	B-Device
extensions	O
to	O
IA-32	B-Device
,	O
called	O
x86-64	B-Device
(	O
later	O
branded	O
AMD64	B-Device
)	O
.	O
</s>
<s>
2000	O
IBM	O
ships	O
its	O
first	O
64-bit	B-Device
z/Architecture	B-Device
mainframe	B-Architecture
,	O
the	O
zSeries	O
z900	O
.	O
</s>
<s>
z/Architecture	B-Device
is	O
a	O
64-bit	B-Device
version	O
of	O
the	O
32-bit	O
ESA/390	O
architecture	O
,	O
a	O
descendant	O
of	O
the	O
32-bit	O
System/360	B-Application
architecture	O
.	O
</s>
<s>
2001	O
Intel	O
ships	O
its	O
IA-64	B-General_Concept
processor	O
line	O
,	O
after	O
repeated	O
delays	O
in	O
getting	O
to	O
market	O
.	O
</s>
<s>
Now	O
branded	O
Itanium	B-General_Concept
and	O
targeting	O
high-end	O
servers	O
,	O
sales	O
fail	O
to	O
meet	O
expectations	O
.	O
</s>
<s>
2003	O
AMD	O
introduces	O
its	O
Opteron	B-General_Concept
and	O
Athlon	O
64	O
processor	O
lines	O
,	O
based	O
on	O
its	O
AMD64	B-Device
architecture	O
which	O
is	O
the	O
first	O
x86-based	O
64-bit	B-Device
processor	I-Device
architecture	O
.	O
</s>
<s>
Apple	O
also	O
ships	O
the	O
64-bit	B-Device
"	O
G5	O
"	O
PowerPC	B-General_Concept
970	I-General_Concept
CPU	O
produced	O
by	O
IBM	O
.	O
</s>
<s>
Intel	O
maintains	O
that	O
its	O
Itanium	B-General_Concept
chips	O
would	O
remain	O
its	O
only	O
64-bit	B-Device
processors	I-Device
.	O
</s>
<s>
2004	O
Intel	O
,	O
reacting	O
to	O
the	O
market	O
success	O
of	O
AMD	O
,	O
admits	O
it	O
has	O
been	O
developing	O
a	O
clone	O
of	O
the	O
AMD64	B-Device
extensions	O
named	O
IA-32e	B-Device
(	O
later	O
renamed	O
EM64T	B-Device
,	O
then	O
yet	O
again	O
renamed	O
to	O
Intel	O
64	O
)	O
.	O
</s>
<s>
Intel	O
ships	O
updated	O
versions	O
of	O
its	O
Xeon	B-Device
and	O
Pentium	B-General_Concept
4	I-General_Concept
processor	O
families	O
supporting	O
the	O
new	O
64-bit	B-Device
instruction	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
VIA	O
Technologies	O
announces	O
the	O
Isaiah	B-Device
64-bit	B-Device
processor	I-Device
.	O
</s>
<s>
2006	O
Sony	O
,	O
IBM	O
,	O
and	O
Toshiba	O
begin	O
manufacturing	O
the	O
64-bit	B-Device
Cell	B-General_Concept
processor	I-General_Concept
for	O
use	O
in	O
the	O
PlayStation	B-Operating_System
3	I-Operating_System
,	O
servers	O
,	O
workstations	B-Device
,	O
and	O
other	O
appliances	O
.	O
</s>
<s>
Intel	O
released	O
Core	B-Device
2	I-Device
Duo	I-Device
as	O
the	O
first	O
mainstream	O
x86-64	B-Device
processor	O
for	O
its	O
mobile	O
,	O
desktop	O
,	O
and	O
workstation	B-Device
line	O
.	O
</s>
<s>
Prior	O
64-bit	B-Device
extension	O
processor	O
lines	O
were	O
not	O
widely	O
available	O
in	O
the	O
consumer	O
retail	O
market	O
(	O
most	O
of	O
64-bit	B-Device
Pentium	B-General_Concept
4/D	O
were	O
OEM	O
)	O
,	O
64-bit	B-Device
Pentium	B-General_Concept
4	I-General_Concept
,	O
Pentium	B-General_Concept
D	O
,	O
and	O
Celeron	B-Device
were	O
not	O
into	O
mass	O
production	O
until	O
late	O
2006	O
due	O
to	O
poor	O
yield	O
issue	O
(	O
most	O
of	O
good	O
yield	O
wafers	O
were	O
targeted	O
at	O
server	B-Application
and	O
mainframe	B-Architecture
while	O
mainstream	O
still	O
remain	O
130nm	O
32-bit	O
processor	O
line	O
until	O
2006	O
)	O
and	O
soon	O
became	O
low	O
end	O
after	O
Core	O
2	O
debuted	O
.	O
</s>
<s>
AMD	O
released	O
their	O
first	O
64-bit	B-Device
mobile	O
processor	O
and	O
manufactured	O
in	O
90nm	O
.	O
</s>
<s>
2011	O
ARM	O
Holdings	O
announces	O
ARMv8-A	O
,	O
the	O
first	O
64-bit	B-Device
version	O
of	O
the	O
ARM	B-Architecture
architecture	I-Architecture
family	I-Architecture
.	O
</s>
<s>
2012	O
ARM	O
Holdings	O
announced	O
their	O
Cortex-A53	O
and	O
Cortex-A57	O
cores	O
,	O
their	O
first	O
cores	O
based	O
on	O
their	O
64-bit	B-Device
architecture	I-Device
,	O
on	O
30	O
October	O
2012	O
.	O
</s>
<s>
2013Apple	O
announces	O
the	O
iPhone	B-Operating_System
5S	I-Operating_System
,	O
with	O
the	O
world	O
's	O
first	O
64-bit	B-Device
processor	I-Device
in	O
a	O
smartphone	O
,	O
which	O
uses	O
their	O
A7	O
ARMv8-A-based	O
system-on-a-chip	O
alongside	O
the	O
iPad	B-Operating_System
Air	I-Operating_System
and	O
iPad	B-Operating_System
Mini	I-Operating_System
2	I-Operating_System
which	O
are	O
the	O
world	O
's	O
first	O
64-bit	B-Device
processor	I-Device
in	O
a	O
tablet	O
.	O
</s>
<s>
2014Google	O
announces	O
the	O
Nexus	B-Device
9	I-Device
tablet	O
,	O
the	O
first	O
Android	B-Application
device	O
to	O
run	O
on	O
the	O
64-bit	B-Device
Tegra	O
K1	O
chip	O
.	O
</s>
<s>
2015Apple	O
announces	O
the	O
iPod	B-Operating_System
Touch	I-Operating_System
(	O
6th	O
generation	O
)	O
,	O
the	O
first	O
iPod	B-Operating_System
Touch	I-Operating_System
to	O
use	O
the	O
64-bit	B-Device
processor	I-Device
A8	O
ARMv8-A-based	O
system-on-a-chip	O
alongside	O
the	O
Apple	B-Device
TV	I-Device
(	O
4th	O
generation	O
)	O
which	O
is	O
the	O
world	O
's	O
first	O
64-bit	B-Device
processor	I-Device
in	O
an	O
Apple	B-Device
TV	I-Device
.	O
</s>
<s>
2018Apple	O
announces	O
the	O
Apple	B-Device
Watch	I-Device
Series	I-Device
4	I-Device
,	O
the	O
first	O
Apple	B-Device
Watch	I-Device
to	O
use	O
the	O
64-bit	B-Device
processor	I-Device
S4	O
ARMv8-A-based	O
system-on-a-chip	O
.	O
</s>
<s>
2020Synopsis	O
announce	O
the	O
ARCv3	O
ISA	O
,	O
the	O
first	O
64-bit	B-Device
version	O
of	O
the	O
ARC	B-Application
ISA	I-Application
.	O
</s>
<s>
1985	O
Cray	O
releases	O
UNICOS	B-Operating_System
,	O
the	O
first	O
64-bit	B-Device
implementation	O
of	O
the	O
Unix	B-Application
operating	I-Application
system	I-Application
.	O
</s>
<s>
1993	O
DEC	O
releases	O
the	O
64-bit	B-Device
DEC	O
OSF/1	O
AXP	O
Unix-like	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
(	O
later	O
renamed	O
Tru64	O
UNIX	B-Application
)	O
for	O
its	O
systems	O
based	O
on	O
the	O
Alpha	B-Device
architecture	O
.	O
</s>
<s>
1994	O
Support	O
for	O
the	O
R8000	B-General_Concept
processor	O
is	O
added	O
by	O
Silicon	O
Graphics	O
to	O
the	O
IRIX	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
in	O
release	O
6.0	O
.	O
</s>
<s>
1995	O
DEC	O
releases	O
OpenVMS	B-Operating_System
7.0	O
,	O
the	O
first	O
full	O
64-bit	B-Device
version	O
of	O
OpenVMS	B-Operating_System
for	O
Alpha	B-Device
.	O
</s>
<s>
First	O
64-bit	B-Device
Linux	B-Application
distribution	I-Application
for	O
the	O
Alpha	B-Device
architecture	O
is	O
released	O
.	O
</s>
<s>
1996	O
Support	O
for	O
the	O
R4x00	O
processors	O
in	O
64-bit	B-Device
mode	O
is	O
added	O
by	O
Silicon	O
Graphics	O
to	O
the	O
IRIX	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
in	O
release	O
6.2	O
.	O
</s>
<s>
1998	O
Sun	O
releases	O
Solaris	B-Application
7	I-Application
,	O
with	O
full	O
64-bit	B-Device
UltraSPARC	B-General_Concept
support	O
.	O
</s>
<s>
2000	O
IBM	O
releases	O
z/OS	B-Application
,	O
a	O
64-bit	B-Device
operating	B-General_Concept
system	I-General_Concept
descended	O
from	O
MVS	B-Application
,	O
for	O
the	O
new	O
zSeries	O
64-bit	B-Device
mainframes	B-Device
;	O
64-bit	B-Device
Linux	B-Application
on	I-Application
z	I-Application
Systems	I-Application
follows	O
the	O
CPU	O
release	O
almost	O
immediately	O
.	O
</s>
<s>
2001	O
Linux	B-Application
becomes	O
the	O
first	O
OS	O
kernel	O
to	O
fully	O
support	O
x86-64	B-Device
(	O
on	O
a	O
simulator	O
,	O
as	O
no	O
x86-64	B-Device
processors	O
had	O
been	O
released	O
yet	O
)	O
.	O
</s>
<s>
2001	O
Microsoft	O
releases	O
Windows	O
XP	O
64-Bit	B-Device
Edition	O
for	O
the	O
Itanium	B-General_Concept
's	O
IA-64	B-General_Concept
architecture	O
;	O
it	O
could	O
run	O
32-bit	O
applications	O
through	O
an	O
execution	O
layer	O
.	O
</s>
<s>
2003	O
Apple	O
releases	O
its	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
10.3	I-Operating_System
"	O
Panther	B-Operating_System
"	O
operating	B-General_Concept
system	I-General_Concept
which	O
adds	O
support	O
for	O
native	O
64-bit	B-Device
integer	O
arithmetic	O
on	O
PowerPC	B-General_Concept
970	I-General_Concept
processors	O
.	O
</s>
<s>
Several	O
Linux	B-Application
distributions	I-Application
release	O
with	O
support	O
for	O
AMD64	B-Device
.	O
</s>
<s>
FreeBSD	B-Operating_System
releases	O
with	O
support	O
for	O
AMD64	B-Device
.	O
</s>
<s>
2005	O
On	O
January	O
4	O
,	O
Microsoft	O
discontinues	O
Windows	O
XP	O
64-Bit	B-Device
Edition	O
,	O
as	O
no	O
PCs	B-Device
with	O
IA-64	B-General_Concept
processors	O
had	O
been	O
available	O
since	O
the	O
previous	O
September	O
,	O
and	O
announces	O
that	O
it	O
is	O
developing	O
x86-64	B-Device
versions	O
of	O
Windows	O
to	O
replace	O
it	O
.	O
</s>
<s>
On	O
January	O
31	O
,	O
Sun	O
releases	O
Solaris	B-Application
10	I-Application
with	O
support	O
for	O
AMD64	B-Device
and	O
EM64T	B-Device
processors	O
.	O
</s>
<s>
On	O
April	O
29	O
,	O
Apple	O
releases	O
Mac	B-Application
OS	I-Application
X	I-Application
10.4	I-Application
"	I-Application
Tiger	I-Application
"	I-Application
which	O
provides	O
limited	O
support	O
for	O
64-bit	B-Device
command-line	O
applications	O
on	O
machines	O
with	O
PowerPC	B-General_Concept
970	I-General_Concept
processors	O
;	O
later	O
versions	O
for	O
Intel-based	O
Macs	O
supported	O
64-bit	B-Device
command-line	O
applications	O
on	O
Macs	O
with	O
EM64T	B-Device
processors	O
.	O
</s>
<s>
On	O
April	O
30	O
,	O
Microsoft	O
releases	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
for	O
AMD64	B-Device
and	O
EM64T	B-Device
processors	O
.	O
</s>
<s>
2006	O
Microsoft	O
releases	O
Windows	B-Application
Vista	I-Application
,	O
including	O
a	O
64-bit	B-Device
version	O
for	O
AMD64/EM64T	O
processors	O
that	O
retains	O
32-bit	O
compatibility	O
.	O
</s>
<s>
In	O
the	O
64-bit	B-Device
version	O
,	O
all	O
Windows	B-Application
applications	I-Application
and	O
components	O
are	O
64-bit	B-Device
,	O
although	O
many	O
also	O
have	O
their	O
32-bit	O
versions	O
included	O
for	O
compatibility	O
with	O
plug-ins	B-Application
.	O
</s>
<s>
2007	O
Apple	O
releases	O
Mac	B-Application
OS	I-Application
X	I-Application
10.5	I-Application
"	I-Application
Leopard	I-Application
"	I-Application
,	O
which	O
fully	O
supports	O
64-bit	B-Device
applications	O
on	O
machines	O
with	O
PowerPC	B-General_Concept
970	I-General_Concept
or	O
EM64T	B-Device
processors	O
.	O
</s>
<s>
2009	O
Microsoft	O
releases	O
Windows	B-Device
7	I-Device
,	O
which	O
,	O
like	O
Windows	B-Application
Vista	I-Application
,	O
includes	O
a	O
full	O
64-bit	B-Device
version	O
for	O
AMD64/Intel	O
64	O
processors	O
;	O
most	O
new	O
computers	O
are	O
loaded	O
by	O
default	O
with	O
a	O
64-bit	B-Device
version	O
.	O
</s>
<s>
Microsoft	O
also	O
releases	O
Windows	B-Device
Server	I-Device
2008	I-Device
R2	I-Device
,	O
which	O
is	O
the	O
first	O
64-bit	B-Device
only	O
server	B-Application
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Apple	O
releases	O
Mac	B-Device
OS	I-Device
X	I-Device
10.6	I-Device
,	O
"	O
Snow	B-Device
Leopard	I-Device
"	O
,	O
which	O
ships	O
with	O
a	O
64-bit	B-Device
kernel	O
for	O
AMD64/Intel64	O
processors	O
,	O
although	O
only	O
certain	O
recent	O
models	O
of	O
Apple	O
computers	O
will	O
run	O
the	O
64-bit	B-Device
kernel	O
by	O
default	O
.	O
</s>
<s>
Most	O
applications	O
bundled	O
with	O
Mac	B-Device
OS	I-Device
X	I-Device
10.6	I-Device
are	O
now	O
also	O
64-bit	B-Device
.	O
</s>
<s>
2011	O
Apple	O
releases	O
Mac	B-Application
OS	I-Application
X	I-Application
10.7	I-Application
,	O
"	O
Lion	B-Application
"	O
,	O
which	O
runs	O
the	O
64-bit	B-Device
kernel	O
by	O
default	O
on	O
supported	O
machines	O
.	O
</s>
<s>
Older	O
machines	O
that	O
are	O
unable	O
to	O
run	O
the	O
64-bit	B-Device
kernel	O
run	O
the	O
32-bit	O
kernel	O
,	O
but	O
,	O
as	O
with	O
earlier	O
releases	O
,	O
can	O
still	O
run	O
64-bit	B-Device
applications	O
;	O
Lion	B-Application
does	O
not	O
support	O
machines	O
with	O
32-bit	O
processors	O
.	O
</s>
<s>
Nearly	O
all	O
applications	O
bundled	O
with	O
Mac	B-Application
OS	I-Application
X	I-Application
10.7	I-Application
are	O
now	O
also	O
64-bit	B-Device
,	O
including	O
iTunes	O
.	O
</s>
<s>
2012	O
Microsoft	O
releases	O
Windows	B-Application
8	I-Application
which	O
supports	O
UEFI	B-Architecture
Class	O
3	O
(	O
UEFI	B-Architecture
without	O
CSM	O
)	O
and	O
Secure	O
Boot	O
.	O
</s>
<s>
2013	O
Apple	O
releases	O
iOS	B-Operating_System
7	I-Operating_System
,	O
which	O
,	O
on	O
machines	O
with	O
AArch64	B-Architecture
processors	O
,	O
has	O
a	O
64-bit	B-Device
kernel	O
that	O
supports	O
64-bit	B-Device
applications	O
.	O
</s>
<s>
2014	O
Google	O
releases	O
Android	B-Application
Lollipop	I-Application
,	O
the	O
first	O
version	O
of	O
the	O
Android	B-Application
operating	I-Application
system	I-Application
with	O
support	O
for	O
64-bit	B-Device
processors	I-Device
.	O
</s>
<s>
2017	O
Apple	O
releases	O
iOS	B-Operating_System
11	I-Operating_System
,	O
supporting	O
only	O
machines	O
with	O
AArch64	B-Architecture
processors	O
.	O
</s>
<s>
It	O
has	O
a	O
64-bit	B-Device
kernel	O
that	O
only	O
supports	O
64-bit	B-Device
applications	O
.	O
</s>
<s>
2018	O
Apple	O
releases	O
watchOS	B-Device
5	I-Device
,	O
the	O
first	O
watchOS	B-Device
version	O
to	O
bring	O
the	O
64-bit	B-Device
support	I-Device
.	O
</s>
<s>
2019	O
Apple	O
releases	O
macOS	B-Device
10.15	I-Device
"	O
Catalina	O
"	O
,	O
dropping	O
support	O
for	O
32-bit	O
Intel	O
applications	O
.	O
</s>
<s>
2021	O
Google	O
releases	O
Android	B-Application
12	I-Application
,	O
dropping	O
support	O
for	O
32-bit	O
applications	O
.	O
</s>
<s>
Microsoft	O
releases	O
Windows	B-Application
11	I-Application
on	O
October	O
5	O
,	O
which	O
only	O
supports	O
64-bit	B-Device
systems	O
,	O
dropping	O
support	O
for	O
IA-32	B-Device
systems	O
.	O
</s>
<s>
2022	O
Apple	O
releases	O
watchOS	B-Device
9	I-Device
,	O
the	O
first	O
watchOS	B-Device
version	O
to	O
run	O
exclusively	O
on	O
the	O
Apple	B-Device
Watch	I-Device
models	O
with	O
64-bit	B-Device
processors	I-Device
(	O
including	O
Apple	B-Device
Watch	I-Device
Series	I-Device
4	I-Device
or	O
newer	O
,	O
Apple	B-Device
Watch	I-Device
SE	O
(	O
1st	O
generation	O
)	O
or	O
newer	O
and	O
the	O
newly	O
introduced	O
Apple	B-Device
Watch	I-Device
Ultra	I-Device
)	O
,	O
dropping	O
support	O
for	O
Apple	B-Device
Watch	I-Device
Series	I-Device
3	I-Device
as	O
the	O
final	O
Apple	B-Device
Watch	I-Device
model	O
with	O
32-bit	O
processor	O
.	O
</s>
<s>
In	O
principle	O
,	O
a	O
64-bit	B-Device
microprocessor	O
can	O
address	O
16EiB	O
(	O
,	O
or	O
about	O
18.4exabytes	O
)	O
of	O
memory	O
.	O
</s>
<s>
However	O
,	O
not	O
all	O
instruction	B-General_Concept
sets	I-General_Concept
,	O
and	O
not	O
all	O
processors	O
implementing	O
those	O
instruction	B-General_Concept
sets	I-General_Concept
,	O
support	O
a	O
full	O
64-bit	B-Device
virtual	O
or	O
physical	O
address	B-General_Concept
space	I-General_Concept
.	O
</s>
<s>
The	O
x86-64	B-Device
architecture	I-Device
(	O
)	O
allows	O
48	O
bits	O
for	O
virtual	B-Architecture
memory	I-Architecture
and	O
,	O
for	O
any	O
given	O
processor	O
,	O
up	O
to	O
52	O
bits	O
for	O
physical	O
memory	O
.	O
</s>
<s>
A	O
PC	B-Device
cannot	O
currently	O
contain	O
4pebibytes	O
of	O
memory	O
(	O
due	O
to	O
the	O
physical	O
size	O
of	O
the	O
memory	O
chips	O
)	O
,	O
but	O
AMD	O
envisioned	O
large	O
servers	O
,	O
shared	O
memory	O
clusters	O
,	O
and	O
other	O
uses	O
of	O
physical	O
address	B-General_Concept
space	I-General_Concept
that	O
might	O
approach	O
this	O
in	O
the	O
foreseeable	O
future	O
.	O
</s>
<s>
Thus	O
the	O
52-bit	O
physical	O
address	O
provides	O
ample	O
room	O
for	O
expansion	O
while	O
not	O
incurring	O
the	O
cost	O
of	O
implementing	O
full	O
64-bit	B-Device
physical	O
addresses	O
.	O
</s>
<s>
Similarly	O
,	O
the	O
48-bit	O
virtual	O
address	B-General_Concept
space	I-General_Concept
was	O
designed	O
to	O
provide	O
65,536	O
(	O
216	O
)	O
times	O
the	O
32-bit	O
limit	O
of	O
4GiB	O
(	O
)	O
,	O
allowing	O
room	O
for	O
later	O
expansion	O
and	O
incurring	O
no	O
overhead	O
of	O
translating	O
full	O
64-bit	B-Device
addresses	O
.	O
</s>
<s>
The	O
Power	B-Architecture
ISA	I-Architecture
v3.0	O
allows	O
64	B-Device
bits	I-Device
for	O
an	O
effective	O
address	O
,	O
mapped	O
to	O
a	O
segmented	O
address	O
with	O
between	O
65	O
and	O
78	O
bits	O
allowed	O
,	O
for	O
virtual	B-Architecture
memory	I-Architecture
,	O
and	O
,	O
for	O
any	O
given	O
processor	O
,	O
up	O
to	O
60	O
bits	O
for	O
physical	O
memory	O
.	O
</s>
<s>
The	O
Oracle	B-Application
SPARC	B-Architecture
Architecture	O
2015	O
allows	O
64	B-Device
bits	I-Device
for	O
virtual	B-Architecture
memory	I-Architecture
and	O
,	O
for	O
any	O
given	O
processor	O
,	O
between	O
40	O
and	O
56	O
bits	O
for	O
physical	O
memory	O
.	O
</s>
<s>
The	O
ARM	O
AArch64	B-Architecture
Virtual	B-Operating_System
Memory	I-Operating_System
System	I-Operating_System
Architecture	O
allows	O
48	O
bits	O
for	O
virtual	B-Architecture
memory	I-Architecture
and	O
,	O
for	O
any	O
given	O
processor	O
,	O
from	O
32	O
to	O
48	O
bits	O
for	O
physical	O
memory	O
.	O
</s>
<s>
The	O
DEC	B-Device
Alpha	I-Device
specification	O
requires	O
minimum	O
of	O
43	O
bits	O
of	O
virtual	B-Architecture
memory	I-Architecture
address	B-General_Concept
space	I-General_Concept
(	O
8TiB	O
)	O
to	O
be	O
supported	O
,	O
and	O
hardware	O
need	O
to	O
check	O
and	O
trap	O
if	O
the	O
remaining	O
unsupported	O
bits	O
are	O
zero	O
(	O
to	O
support	O
compatibility	O
on	O
future	O
processors	O
)	O
.	O
</s>
<s>
Alpha	B-General_Concept
21064	I-General_Concept
supported	O
43	O
bits	O
of	O
virtual	B-Architecture
memory	B-General_Concept
address	I-General_Concept
space	I-General_Concept
(	O
8TiB	O
)	O
and	O
34	O
bits	O
of	O
physical	O
memory	B-General_Concept
address	I-General_Concept
space	I-General_Concept
(	O
16GiB	O
)	O
.	O
</s>
<s>
Alpha	B-General_Concept
21164	I-General_Concept
supported	O
43	O
bits	O
of	O
virtual	B-Architecture
memory	B-General_Concept
address	I-General_Concept
space	I-General_Concept
(	O
8TiB	O
)	O
and	O
40	O
bits	O
of	O
physical	O
memory	B-General_Concept
address	I-General_Concept
space	I-General_Concept
(	O
1TiB	O
)	O
.	O
</s>
<s>
Alpha	B-General_Concept
21264	I-General_Concept
supported	O
user-configurable	O
43	O
or	O
48	O
bits	O
of	O
virtual	B-Architecture
memory	B-General_Concept
address	I-General_Concept
space	I-General_Concept
(	O
8TiB	O
or	O
256TiB	O
)	O
and	O
44	O
bits	O
of	O
physical	O
memory	B-General_Concept
address	I-General_Concept
space	I-General_Concept
(	O
16TiB	O
)	O
.	O
</s>
<s>
A	O
change	O
from	O
a	O
32-bit	O
to	O
a	O
64-bit	B-Device
architecture	I-Device
is	O
a	O
fundamental	O
alteration	O
,	O
as	O
most	O
operating	B-General_Concept
systems	I-General_Concept
must	O
be	O
extensively	O
modified	O
to	O
take	O
advantage	O
of	O
the	O
new	O
architecture	O
,	O
because	O
that	O
software	O
has	O
to	O
manage	O
the	O
actual	O
memory	B-General_Concept
addressing	I-General_Concept
hardware	O
.	O
</s>
<s>
Other	O
software	O
must	O
also	O
be	O
ported	O
to	O
use	O
the	O
new	O
abilities	O
;	O
older	O
32-bit	O
software	O
may	O
be	O
supported	O
either	O
by	O
virtue	O
of	O
the	O
64-bit	B-Device
instruction	B-General_Concept
set	I-General_Concept
being	O
a	O
superset	O
of	O
the	O
32-bit	O
instruction	B-General_Concept
set	I-General_Concept
,	O
so	O
that	O
processors	O
that	O
support	O
the	O
64-bit	B-Device
instruction	B-General_Concept
set	I-General_Concept
can	O
also	O
run	O
code	O
for	O
the	O
32-bit	O
instruction	B-General_Concept
set	I-General_Concept
,	O
or	O
through	O
software	B-Application
emulation	I-Application
,	O
or	O
by	O
the	O
actual	O
implementation	O
of	O
a	O
32-bit	O
processor	O
core	O
within	O
the	O
64-bit	B-Device
processor	I-Device
,	O
as	O
with	O
some	O
Itanium	B-General_Concept
processors	O
from	O
Intel	O
,	O
which	O
included	O
an	O
IA-32	B-Device
processor	O
core	O
to	O
run	O
32-bit	B-Device
x86	I-Device
applications	O
.	O
</s>
<s>
The	O
operating	B-General_Concept
systems	I-General_Concept
for	O
those	O
64-bit	B-Device
architectures	I-Device
generally	O
support	O
both	O
32-bit	O
and	O
64-bit	B-Device
applications	O
.	O
</s>
<s>
One	O
significant	O
exception	O
to	O
this	O
is	O
the	O
IBM	B-Device
AS/400	I-Device
,	O
software	O
for	O
which	O
is	O
compiled	O
into	O
a	O
virtual	O
instruction	B-General_Concept
set	I-General_Concept
architecture	I-General_Concept
(	O
ISA	O
)	O
called	O
Technology	O
Independent	O
Machine	O
Interface	O
(	O
TIMI	O
)	O
;	O
TIMI	O
code	O
is	O
then	O
translated	O
to	O
native	O
machine	B-Language
code	I-Language
by	O
low-level	O
software	O
before	O
being	O
executed	O
.	O
</s>
<s>
The	O
translation	O
software	O
is	O
all	O
that	O
must	O
be	O
rewritten	O
to	O
move	O
the	O
full	O
OS	O
and	O
all	O
software	O
to	O
a	O
new	O
platform	O
,	O
as	O
when	O
IBM	O
transitioned	O
the	O
native	O
instruction	B-General_Concept
set	I-General_Concept
for	O
AS/400	B-Device
from	O
the	O
older	O
32/48	O
-bit	O
IMPI	O
to	O
the	O
newer	O
64-bit	B-Device
PowerPC-AS	O
,	O
codenamed	O
Amazon	O
.	O
</s>
<s>
The	O
IMPI	O
instruction	B-General_Concept
set	I-General_Concept
was	O
quite	O
different	O
from	O
even	O
32-bit	O
PowerPC	B-Architecture
,	O
so	O
this	O
transition	O
was	O
even	O
bigger	O
than	O
moving	O
a	O
given	O
instruction	B-General_Concept
set	I-General_Concept
from	O
32	O
to	O
64	B-Device
bits	I-Device
.	O
</s>
<s>
On	O
64-bit	B-Device
hardware	O
with	O
x86-64	B-Device
architecture	I-Device
(	O
AMD64	B-Device
)	O
,	O
most	O
32-bit	O
operating	B-General_Concept
systems	I-General_Concept
and	O
applications	O
can	O
run	O
with	O
no	O
compatibility	O
issues	O
.	O
</s>
<s>
While	O
the	O
larger	O
address	B-General_Concept
space	I-General_Concept
of	O
64-bit	B-Device
architectures	I-Device
makes	O
working	O
with	O
large	O
data	B-General_Concept
sets	O
in	O
applications	O
such	O
as	O
digital	O
video	O
,	O
scientific	O
computing	O
,	O
and	O
large	O
databases	O
easier	O
,	O
there	O
has	O
been	O
considerable	O
debate	O
on	O
whether	O
they	O
or	O
their	O
32-bit	O
compatibility	B-Application
modes	I-Application
will	O
be	O
faster	O
than	O
comparably	O
priced	O
32-bit	O
systems	O
for	O
other	O
tasks	O
.	O
</s>
<s>
A	O
compiled	O
Java	O
program	O
can	O
run	O
on	O
a	O
32	O
-	O
or	O
64-bit	B-Device
Java	O
virtual	B-Architecture
machine	I-Architecture
with	O
no	O
modification	O
.	O
</s>
<s>
The	O
lengths	O
and	O
precision	O
of	O
all	O
the	O
built-in	O
types	O
,	O
such	O
as	O
char	O
,	O
short	O
,	O
int	O
,	O
long	O
,	O
float	B-Algorithm
,	O
and	O
double	O
,	O
and	O
the	O
types	O
that	O
can	O
be	O
used	O
as	O
array	O
indices	O
,	O
are	O
specified	O
by	O
the	O
standard	O
and	O
are	O
not	O
dependent	O
on	O
the	O
underlying	O
architecture	O
.	O
</s>
<s>
Java	O
programs	O
that	O
run	O
on	O
a	O
64-bit	B-Device
Java	O
virtual	B-Architecture
machine	I-Architecture
have	O
access	O
to	O
a	O
larger	O
address	B-General_Concept
space	I-General_Concept
.	O
</s>
<s>
Speed	O
is	O
not	O
the	O
only	O
factor	O
to	O
consider	O
in	O
comparing	O
32-bit	O
and	O
64-bit	B-Device
processors	I-Device
.	O
</s>
<s>
Applications	O
such	O
as	O
multi-tasking	O
,	O
stress	O
testing	O
,	O
and	O
clustering	O
–	O
for	O
high-performance	B-Architecture
computing	I-Architecture
(	O
HPC	O
)	O
–	O
may	O
be	O
more	O
suited	O
to	O
a	O
64-bit	B-Device
architecture	I-Device
when	O
deployed	O
appropriately	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
64-bit	B-Device
clusters	O
have	O
been	O
widely	O
deployed	O
in	O
large	O
organizations	O
,	O
such	O
as	O
IBM	O
,	O
HP	O
,	O
and	O
Microsoft	O
.	O
</s>
<s>
A	O
64-bit	B-Device
processor	I-Device
performs	O
best	O
with	O
64-bit	B-Device
software	O
.	O
</s>
<s>
A	O
64-bit	B-Device
processor	I-Device
may	O
have	O
backward	B-General_Concept
compatibility	I-General_Concept
,	O
allowing	O
it	O
to	O
run	O
32-bit	O
application	O
software	O
for	O
the	O
32-bit	O
version	O
of	O
its	O
instruction	B-General_Concept
set	I-General_Concept
,	O
and	O
may	O
also	O
support	O
running	O
32-bit	O
operating	B-General_Concept
systems	I-General_Concept
for	O
the	O
32-bit	O
version	O
of	O
its	O
instruction	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
A	O
32-bit	O
processor	O
is	O
incompatible	O
with	O
64-bit	B-Device
software	O
.	O
</s>
<s>
A	O
common	O
misconception	O
is	O
that	O
64-bit	B-Device
architectures	I-Device
are	O
no	O
better	O
than	O
32-bit	O
architectures	O
unless	O
the	O
computer	O
has	O
more	O
than	O
4GiB	O
of	O
random-access	B-Architecture
memory	I-Architecture
.	O
</s>
<s>
Some	O
operating	B-General_Concept
systems	I-General_Concept
and	O
certain	O
hardware	O
configurations	O
limit	O
the	O
physical	O
memory	O
space	O
to	O
3GiB	O
on	O
IA-32	B-Device
systems	O
,	O
due	O
to	O
much	O
of	O
the	O
3	O
–	O
4GiB	O
region	O
being	O
reserved	O
for	O
hardware	O
addressing	O
;	O
see	O
3	B-Device
GiB	I-Device
barrier	I-Device
;	O
64-bit	B-Device
architectures	I-Device
can	O
address	O
far	O
more	O
than	O
4GiB	O
.	O
</s>
<s>
However	O
,	O
IA-32	B-Device
processors	O
from	O
the	O
Pentium	B-Device
Pro	I-Device
onward	O
allow	O
a	O
36-bit	O
physical	O
memory	B-General_Concept
address	I-General_Concept
space	O
,	O
using	O
Physical	B-General_Concept
Address	I-General_Concept
Extension	I-General_Concept
(	O
PAE	O
)	O
,	O
which	O
gives	O
a	O
64GiB	O
physical	O
address	B-General_Concept
range	I-General_Concept
,	O
of	O
which	O
up	O
to	O
62GiB	O
may	O
be	O
used	O
by	O
main	O
memory	O
;	O
operating	B-General_Concept
systems	I-General_Concept
that	O
support	O
PAE	O
may	O
not	O
be	O
limited	O
to	O
4GiB	O
of	O
physical	O
memory	O
,	O
even	O
on	O
IA-32	B-Device
processors	O
.	O
</s>
<s>
However	O
,	O
drivers	O
and	O
other	O
kernel	O
mode	O
software	O
,	O
more	O
so	O
older	O
versions	O
,	O
may	O
be	O
incompatible	O
with	O
PAE	O
;	O
this	O
has	O
been	O
cited	O
as	O
the	O
reason	O
for	O
32-bit	O
versions	O
of	O
Microsoft	B-Application
Windows	I-Application
being	O
limited	O
to	O
4GiB	O
of	O
physical	O
RAM	B-Architecture
(	O
although	O
the	O
validity	O
of	O
this	O
explanation	O
has	O
been	O
disputed	O
)	O
.	O
</s>
<s>
Some	O
operating	B-General_Concept
systems	I-General_Concept
reserve	O
portions	O
of	O
process	B-Operating_System
address	B-General_Concept
space	I-General_Concept
for	O
OS	O
use	O
,	O
effectively	O
reducing	O
the	O
total	O
address	B-General_Concept
space	I-General_Concept
available	O
for	O
mapping	O
memory	O
for	O
user	O
programs	O
.	O
</s>
<s>
For	O
instance	O
,	O
32-bit	B-Application
Windows	I-Application
reserves	O
1	O
or	O
2GiB	O
(	O
depending	O
on	O
the	O
settings	O
)	O
of	O
the	O
total	O
address	B-General_Concept
space	I-General_Concept
for	O
the	O
kernel	O
,	O
which	O
leaves	O
only	O
3	O
or	O
2GiB	O
(	O
respectively	O
)	O
of	O
the	O
address	B-General_Concept
space	I-General_Concept
available	O
for	O
user	O
mode	O
.	O
</s>
<s>
This	O
limit	O
is	O
much	O
higher	O
on	O
64-bit	B-Device
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Memory-mapped	B-General_Concept
files	I-General_Concept
are	O
becoming	O
more	O
difficult	O
to	O
implement	O
in	O
32-bit	O
architectures	O
as	O
files	O
of	O
over	O
4GiB	O
become	O
more	O
common	O
;	O
such	O
large	O
files	O
cannot	O
be	O
memory-mapped	O
easily	O
to	O
32-bit	O
architectures	O
,	O
as	O
only	O
part	O
of	O
the	O
file	O
can	O
be	O
mapped	O
into	O
the	O
address	B-General_Concept
space	I-General_Concept
at	O
a	O
time	O
,	O
and	O
to	O
access	O
such	O
a	O
file	O
by	O
memory	O
mapping	O
,	O
the	O
parts	O
mapped	O
must	O
be	O
swapped	O
into	O
and	O
out	O
of	O
the	O
address	B-General_Concept
space	I-General_Concept
as	O
needed	O
.	O
</s>
<s>
Some	O
64-bit	B-Device
programs	O
,	O
such	O
as	O
encoders	O
,	O
decoders	O
and	O
encryption	O
software	O
,	O
can	O
benefit	O
greatly	O
from	O
64-bit	B-Device
registers	B-General_Concept
,	O
while	O
the	O
performance	O
of	O
other	O
programs	O
,	O
such	O
as	O
3D	O
graphics-oriented	O
ones	O
,	O
remains	O
unaffected	O
when	O
switching	O
from	O
a	O
32-bit	O
to	O
a	O
64-bit	B-Device
environment	O
.	O
</s>
<s>
Some	O
64-bit	B-Device
architectures	I-Device
,	O
such	O
as	O
x86-64	B-Device
and	O
AArch64	B-Architecture
,	O
support	O
more	O
general-purpose	O
registers	B-General_Concept
than	O
their	O
32-bit	O
counterparts	O
(	O
although	O
this	O
is	O
not	O
due	O
specifically	O
to	O
the	O
word	O
length	O
)	O
.	O
</s>
<s>
This	O
leads	O
to	O
a	O
significant	O
speed	O
increase	O
for	O
tight	O
loops	O
since	O
the	O
processor	O
does	O
not	O
have	O
to	O
fetch	O
data	B-General_Concept
from	O
the	O
cache	O
or	O
main	O
memory	O
if	O
the	O
data	B-General_Concept
can	O
fit	O
in	O
the	O
available	O
registers	B-General_Concept
.	O
</s>
<s>
Example	O
in	O
C	B-Language
:	O
</s>
<s>
This	O
code	O
first	O
creates	O
5	O
values	O
:	O
a	O
,	O
b	O
,	O
c	B-Language
,	O
d	O
and	O
e	O
;	O
and	O
then	O
puts	O
them	O
in	O
a	O
loop	O
.	O
</s>
<s>
During	O
the	O
loop	O
,	O
this	O
code	O
changes	O
the	O
value	O
of	O
b	O
to	O
the	O
value	O
of	O
a	O
,	O
the	O
value	O
of	O
c	B-Language
to	O
the	O
value	O
of	O
b	O
,	O
the	O
value	O
of	O
d	O
to	O
the	O
value	O
of	O
c	B-Language
and	O
the	O
value	O
of	O
e	O
to	O
the	O
value	O
of	O
d	O
.	O
This	O
has	O
the	O
same	O
effect	O
as	O
changing	O
all	O
the	O
values	O
to	O
a	O
.	O
</s>
<s>
If	O
a	O
processor	O
can	O
keep	O
only	O
two	O
or	O
three	O
values	O
or	O
variables	O
in	O
registers	B-General_Concept
,	O
it	O
would	O
need	O
to	O
move	O
some	O
values	O
between	O
memory	O
and	O
registers	B-General_Concept
to	O
be	O
able	O
to	O
process	B-Operating_System
variables	O
d	O
and	O
e	O
also	O
;	O
this	O
is	O
a	O
process	B-Operating_System
that	O
takes	O
many	O
CPU	O
cycles	O
.	O
</s>
<s>
A	O
processor	O
that	O
can	O
hold	O
all	O
values	O
and	O
variables	O
in	O
registers	B-General_Concept
can	O
loop	O
through	O
them	O
with	O
no	O
need	O
to	O
move	O
data	B-General_Concept
between	O
registers	B-General_Concept
and	O
memory	O
for	O
each	O
iteration	O
.	O
</s>
<s>
This	O
behavior	O
can	O
easily	O
be	O
compared	O
with	O
virtual	B-Architecture
memory	I-Architecture
,	O
although	O
any	O
effects	O
are	O
contingent	O
on	O
the	O
compiler	O
.	O
</s>
<s>
The	O
main	O
disadvantage	O
of	O
64-bit	B-Device
architectures	I-Device
is	O
that	O
,	O
relative	O
to	O
32-bit	O
architectures	O
,	O
the	O
same	O
data	B-General_Concept
occupies	O
more	O
space	O
in	O
memory	O
(	O
due	O
to	O
longer	O
pointers	O
and	O
possibly	O
other	O
types	O
,	O
and	O
alignment	O
padding	O
)	O
.	O
</s>
<s>
This	O
increases	O
the	O
memory	O
requirements	O
of	O
a	O
given	O
process	B-Operating_System
and	O
can	O
have	O
implications	O
for	O
efficient	O
processor	O
cache	O
use	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
z/OS	B-Application
operating	B-General_Concept
system	I-General_Concept
takes	O
this	O
approach	O
,	O
requiring	O
program	O
code	O
to	O
reside	O
in	O
31-bit	O
address	B-General_Concept
spaces	I-General_Concept
(	O
the	O
high	O
order	O
bit	O
is	O
not	O
used	O
in	O
address	O
calculation	O
on	O
the	O
underlying	O
hardware	O
platform	O
)	O
while	O
data	B-General_Concept
objects	O
can	O
optionally	O
reside	O
in	O
64-bit	B-Device
regions	O
.	O
</s>
<s>
Not	O
all	O
such	O
applications	O
require	O
a	O
large	O
address	B-General_Concept
space	I-General_Concept
or	O
manipulate	O
64-bit	B-Device
data	B-General_Concept
items	O
,	O
so	O
these	O
applications	O
do	O
not	O
benefit	O
from	O
these	O
features	O
.	O
</s>
<s>
x86-based	O
64-bit	B-Device
systems	O
sometimes	O
lack	O
equivalents	O
of	O
software	O
that	O
is	O
written	O
for	O
32-bit	O
architectures	O
.	O
</s>
<s>
The	O
most	O
severe	O
problem	O
in	O
Microsoft	B-Application
Windows	I-Application
is	O
incompatible	O
device	B-Application
drivers	I-Application
for	O
obsolete	O
hardware	O
.	O
</s>
<s>
Most	O
32-bit	O
application	O
software	O
can	O
run	O
on	O
a	O
64-bit	B-Device
operating	B-General_Concept
system	I-General_Concept
in	O
a	O
compatibility	B-Application
mode	I-Application
,	O
also	O
termed	O
an	O
emulation	B-Application
mode	O
,	O
e.g.	O
,	O
Microsoft	O
WoW64	B-Application
Technology	O
for	O
IA-64	B-General_Concept
and	O
AMD64	B-Device
.	O
</s>
<s>
The	O
64-bit	B-Device
Windows	O
Native	O
Mode	O
driver	O
environment	O
runs	O
atop	O
64-bit	B-Device
,	O
which	O
cannot	O
call	O
32-bit	O
Win32	O
subsystem	O
code	O
(	O
often	O
devices	O
whose	O
actual	O
hardware	O
function	O
is	O
emulated	B-Application
in	O
user	O
mode	O
software	O
,	O
like	O
Winprinters	O
)	O
.	O
</s>
<s>
Because	O
64-bit	B-Device
drivers	O
for	O
most	O
devices	O
were	O
unavailable	O
until	O
early	O
2007	O
(	O
Vista	B-Application
x64	B-Device
)	O
,	O
using	O
a	O
64-bit	B-Device
version	O
of	O
Windows	O
was	O
considered	O
a	O
challenge	O
.	O
</s>
<s>
However	O
,	O
the	O
trend	O
has	O
since	O
moved	O
toward	O
64-bit	B-Device
computing	I-Device
,	O
more	O
so	O
as	O
memory	O
prices	O
dropped	O
and	O
the	O
use	O
of	O
more	O
than	O
4GiB	O
of	O
RAM	B-Architecture
increased	O
.	O
</s>
<s>
Most	O
manufacturers	O
started	O
to	O
provide	O
both	O
32-bit	O
and	O
64-bit	B-Device
drivers	O
for	O
new	O
devices	O
,	O
so	O
unavailability	O
of	O
64-bit	B-Device
drivers	O
ceased	O
to	O
be	O
a	O
problem	O
.	O
</s>
<s>
64-bit	B-Device
drivers	O
were	O
not	O
provided	O
for	O
many	O
older	O
devices	O
,	O
which	O
could	O
consequently	O
not	O
be	O
used	O
in	O
64-bit	B-Device
systems	O
.	O
</s>
<s>
Driver	O
compatibility	O
was	O
less	O
of	O
a	O
problem	O
with	O
open-source	B-Application
drivers	O
,	O
as	O
32-bit	O
ones	O
could	O
be	O
modified	O
for	O
64-bit	B-Device
use	O
.	O
</s>
<s>
Support	O
for	O
hardware	O
made	O
before	O
early	O
2007	O
,	O
was	O
problematic	O
for	O
open-source	B-Application
platforms	I-Application
,	O
due	O
to	O
the	O
relatively	O
small	O
number	O
of	O
users	O
.	O
</s>
<s>
64-bit	B-Device
versions	O
of	O
Windows	O
cannot	O
run	O
16-bit	O
software	O
.	O
</s>
<s>
64-bit	B-Device
users	O
are	O
forced	O
to	O
install	O
a	O
virtual	B-Architecture
machine	I-Architecture
of	O
a	O
16	O
-	O
or	O
32-bit	O
operating	B-General_Concept
system	I-General_Concept
to	O
run	O
16-bit	O
applications	O
or	O
use	O
one	O
of	O
the	O
alternatives	O
for	O
NTVDM	O
.	O
</s>
<s>
Mac	B-Application
OS	I-Application
X	I-Application
10.4	I-Application
"	I-Application
Tiger	I-Application
"	I-Application
and	O
Mac	B-Application
OS	I-Application
X	I-Application
10.5	I-Application
"	I-Application
Leopard	I-Application
"	I-Application
had	O
only	O
a	O
32-bit	O
kernel	O
,	O
but	O
they	O
can	O
run	O
64-bit	B-Device
user-mode	O
code	O
on	O
64-bit	B-Device
processors	I-Device
.	O
</s>
<s>
Mac	B-Device
OS	I-Device
X	I-Device
10.6	I-Device
"	O
Snow	B-Device
Leopard	I-Device
"	O
had	O
both	O
32	O
-	O
and	O
64-bit	B-Device
kernels	O
,	O
and	O
,	O
on	O
most	O
Macs	O
,	O
used	O
the	O
32-bit	O
kernel	O
even	O
on	O
64-bit	B-Device
processors	I-Device
.	O
</s>
<s>
This	O
allowed	O
those	O
Macs	O
to	O
support	O
64-bit	B-Device
processes	O
while	O
still	O
supporting	O
32-bit	O
device	B-Application
drivers	I-Application
;	O
although	O
not	O
64-bit	B-Device
drivers	O
and	O
performance	O
advantages	O
that	O
can	O
come	O
with	O
them	O
.	O
</s>
<s>
Mac	B-Application
OS	I-Application
X	I-Application
10.7	I-Application
"	O
Lion	B-Application
"	O
ran	O
with	O
a	O
64-bit	B-Device
kernel	O
on	O
more	O
Macs	O
,	O
and	O
OS	B-Operating_System
X	I-Operating_System
10.8	I-Operating_System
"	O
Mountain	O
Lion	B-Application
"	O
and	O
later	O
macOS	B-Application
releases	O
only	O
have	O
a	O
64-bit	B-Device
kernel	O
.	O
</s>
<s>
On	O
systems	O
with	O
64-bit	B-Device
processors	I-Device
,	O
both	O
the	O
32	O
-	O
and	O
64-bit	B-Device
macOS	B-Application
kernels	O
can	O
run	O
32-bit	O
user-mode	O
code	O
,	O
and	O
all	O
versions	O
of	O
macOS	B-Application
up	O
to	O
macOS	B-Application
Mojave	O
(	O
10.14	O
)	O
include	O
32-bit	O
versions	O
of	O
libraries	O
that	O
32-bit	O
applications	O
would	O
use	O
,	O
so	O
32-bit	O
user-mode	O
software	O
for	O
macOS	B-Application
will	O
run	O
on	O
those	O
systems	O
.	O
</s>
<s>
The	O
32-bit	O
versions	O
of	O
libraries	O
have	O
been	O
removed	O
by	O
Apple	O
in	O
macOS	B-Device
Catalina	I-Device
(	O
10.15	O
)	O
.	O
</s>
<s>
Linux	B-Application
and	O
most	O
other	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
and	O
the	O
C	B-Language
and	O
C++	B-Language
toolchains	B-General_Concept
for	O
them	O
,	O
have	O
supported	O
64-bit	B-Device
processors	I-Device
for	O
many	O
years	O
.	O
</s>
<s>
Many	O
applications	O
and	O
libraries	O
for	O
those	O
platforms	O
are	O
open-source	B-Application
software	I-Application
,	O
written	O
in	O
C	B-Language
and	O
C++	B-Language
,	O
so	O
that	O
if	O
they	O
are	O
64-bit-safe	O
,	O
they	O
can	O
be	O
compiled	O
into	O
64-bit	B-Device
versions	O
.	O
</s>
<s>
This	O
source-based	O
distribution	O
model	O
,	O
with	O
an	O
emphasis	O
on	O
frequent	O
releases	O
,	O
makes	O
availability	O
of	O
application	O
software	O
for	O
those	O
operating	B-General_Concept
systems	I-General_Concept
less	O
of	O
an	O
issue	O
.	O
</s>
<s>
In	O
32-bit	O
programs	O
,	O
pointers	O
and	O
data	B-General_Concept
types	O
such	O
as	O
integers	O
generally	O
have	O
the	O
same	O
length	O
.	O
</s>
<s>
This	O
is	O
not	O
necessarily	O
true	O
on	O
64-bit	B-Device
machines	O
.	O
</s>
<s>
Mixing	O
data	B-General_Concept
types	O
in	O
programming	O
languages	O
such	O
as	O
C	B-Language
and	O
its	O
descendants	O
such	O
as	O
C++	B-Language
and	O
Objective-C	B-Language
may	O
thus	O
work	O
on	O
32-bit	O
implementations	O
but	O
not	O
on	O
64-bit	B-Device
implementations	O
.	O
</s>
<s>
In	O
many	O
programming	O
environments	O
for	O
C	B-Language
and	O
C-derived	O
languages	O
on	O
64-bit	B-Device
machines	O
,	O
int	O
variables	O
are	O
still	O
32	O
bits	O
wide	O
,	O
but	O
long	O
integers	O
and	O
pointers	O
are	O
64	B-Device
bits	I-Device
wide	O
.	O
</s>
<s>
These	O
are	O
described	O
as	O
having	O
an	O
LP64	O
data	B-Application
model	I-Application
,	O
which	O
is	O
an	O
abbreviation	O
of	O
"	O
Long	O
,	O
Pointer	O
,	O
64	O
"	O
.	O
</s>
<s>
Other	O
models	O
are	O
the	O
ILP64	O
data	B-Application
model	I-Application
in	O
which	O
all	O
three	O
data	B-General_Concept
types	O
are	O
64	B-Device
bits	I-Device
wide	O
,	O
and	O
even	O
the	O
SILP64	O
model	O
where	O
short	O
integers	O
are	O
also	O
64	B-Device
bits	I-Device
wide	O
.	O
</s>
<s>
LL	O
refers	O
to	O
the	O
long	O
long	O
integer	O
type	O
,	O
which	O
is	O
at	O
least	O
64	B-Device
bits	I-Device
on	O
all	O
platforms	O
,	O
including	O
32-bit	O
environments	O
.	O
</s>
<s>
There	O
are	O
also	O
systems	O
with	O
64-bit	B-Device
processors	I-Device
using	O
an	O
ILP32	O
data	B-Application
model	I-Application
,	O
with	O
the	O
addition	O
of	O
64-bit	B-Device
long	O
long	O
integers	O
;	O
this	O
is	O
also	O
used	O
on	O
many	O
platforms	O
with	O
32-bit	O
processors	O
.	O
</s>
<s>
This	O
model	O
reduces	O
code	O
size	O
and	O
the	O
size	O
of	O
data	B-General_Concept
structures	O
containing	O
pointers	O
,	O
at	O
the	O
cost	O
of	O
a	O
much	O
smaller	O
address	B-General_Concept
space	I-General_Concept
,	O
a	O
good	O
choice	O
for	O
some	O
embedded	O
systems	O
.	O
</s>
<s>
For	O
instruction	B-General_Concept
sets	I-General_Concept
such	O
as	O
x86	B-Operating_System
and	O
ARM	O
in	O
which	O
the	O
64-bit	B-Device
version	O
of	O
the	O
instruction	B-General_Concept
set	I-General_Concept
has	O
more	O
registers	B-General_Concept
than	O
does	O
the	O
32-bit	O
version	O
,	O
it	O
provides	O
access	O
to	O
the	O
additional	O
registers	B-General_Concept
without	O
the	O
space	O
penalty	O
.	O
</s>
<s>
It	O
is	O
common	O
in	O
64-bit	B-Device
RISC	B-Architecture
machines	O
,	O
explored	O
in	O
x86	B-Operating_System
as	O
x32	B-Application
ABI	I-Application
,	O
and	O
has	O
recently	O
been	O
used	O
in	O
the	O
Apple	B-Device
Watch	I-Device
Series	I-Device
4	I-Device
and	O
5	O
.	O
</s>
<s>
+	O
64-bit	B-Device
data	B-Application
models	I-Application
Data	B-Application
model	I-Application
(	O
integer	O
)	O
(	O
integer	O
)	O
pointers	O
,	O
Sample	O
operating	B-General_Concept
systems	I-General_Concept
ILP32	O
16	O
32	O
32	O
64	O
32	O
x32	O
and	O
ABIs	O
on	O
Linux	B-Application
systems	O
;	O
MIPS	O
N32	O
ABI	O
.	O
</s>
<s>
LLP64	O
16	O
32	O
32	O
64	O
64	O
Microsoft	B-Application
Windows	I-Application
(	O
x86-64	B-Device
and	O
IA-64	B-General_Concept
)	O
using	O
Visual	B-Application
C++	I-Application
;	O
and	O
MinGW	B-Application
LP64	O
16	O
32	O
64	O
64	O
64	O
Most	O
Unix	B-Application
and	O
Unix-like	B-Operating_System
systems	I-Operating_System
,	O
e.g.	O
,	O
Solaris	B-Application
,	O
Linux	B-Application
,	O
BSD	B-Operating_System
,	O
macOS	B-Application
.	O
</s>
<s>
Windows	O
when	O
using	O
Cygwin	B-Language
;	O
z/OS	B-Application
ILP64	O
16	O
64	O
64	O
64	O
64	O
HAL	O
Computer	O
Systems	O
port	O
of	O
Solaris	B-Application
to	O
the	O
SPARC64	B-General_Concept
SILP64	O
64	O
64	O
64	O
64	O
64	O
Classic	O
UNICOS	B-Operating_System
(	O
versus	O
UNICOS/mp	O
,	O
etc	O
.	O
)	O
</s>
<s>
Many	O
64-bit	B-Device
platforms	O
today	O
use	O
an	O
LP64	O
model	O
(	O
including	O
Solaris	B-Application
,	O
AIX	B-Application
,	O
HP-UX	B-Application
,	O
Linux	B-Application
,	O
macOS	B-Application
,	O
BSD	B-Operating_System
,	O
and	O
IBM	B-Application
z/OS	I-Application
)	O
.	O
</s>
<s>
Microsoft	B-Application
Windows	I-Application
uses	O
an	O
LLP64	O
model	O
.	O
</s>
<s>
These	O
are	O
not	O
problems	O
which	O
affect	O
fully	O
standard-compliant	O
code	O
,	O
but	O
code	O
is	O
often	O
written	O
with	O
implicit	O
assumptions	O
about	O
the	O
widths	O
of	O
data	B-General_Concept
types	O
.	O
</s>
<s>
C	B-Language
code	O
should	O
prefer	O
(	O
u	O
)	O
intptr_t	O
instead	O
of	O
long	O
when	O
casting	O
pointers	O
into	O
integer	O
objects	O
.	O
</s>
<s>
However	O
,	O
the	O
programming	O
model	O
chosen	O
as	O
the	O
primary	O
model	O
for	O
the	O
OS	O
application	B-Application
programming	I-Application
interface	I-Application
(	O
API	B-Application
)	O
typically	O
dominates	O
.	O
</s>
<s>
Another	O
consideration	O
is	O
the	O
data	B-Application
model	I-Application
used	O
for	O
device	B-Application
drivers	I-Application
.	O
</s>
<s>
Drivers	O
make	O
up	O
the	O
majority	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
code	O
in	O
most	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
(	O
although	O
many	O
may	O
not	O
be	O
loaded	O
when	O
the	O
operating	B-General_Concept
system	I-General_Concept
is	O
running	O
)	O
.	O
</s>
<s>
Many	O
drivers	O
use	O
pointers	O
heavily	O
to	O
manipulate	O
data	B-General_Concept
,	O
and	O
in	O
some	O
cases	O
have	O
to	O
load	O
pointers	O
of	O
a	O
certain	O
size	O
into	O
the	O
hardware	O
they	O
support	O
for	O
direct	B-General_Concept
memory	I-General_Concept
access	I-General_Concept
(	O
DMA	O
)	O
.	O
</s>
<s>
As	O
an	O
example	O
,	O
a	O
driver	O
for	O
a	O
32-bit	O
PCI	O
device	O
asking	O
the	O
device	O
to	O
DMA	O
data	B-General_Concept
into	O
upper	O
areas	O
of	O
a	O
64-bit	B-Device
machine	O
's	O
memory	O
could	O
not	O
satisfy	O
requests	O
from	O
the	O
operating	B-General_Concept
system	I-General_Concept
to	O
load	O
data	B-General_Concept
from	O
the	O
device	O
to	O
memory	O
above	O
the	O
4	O
gibibyte	O
barrier	O
,	O
because	O
the	O
pointers	O
for	O
those	O
addresses	O
would	O
not	O
fit	O
into	O
the	O
DMA	O
registers	B-General_Concept
of	O
the	O
device	O
.	O
</s>
<s>
This	O
problem	O
is	O
solved	O
by	O
having	O
the	O
OS	O
take	O
the	O
memory	O
restrictions	O
of	O
the	O
device	O
into	O
account	O
when	O
generating	O
requests	O
to	O
drivers	O
for	O
DMA	O
,	O
or	O
by	O
using	O
an	O
input	B-General_Concept
–	I-General_Concept
output	I-General_Concept
memory	I-General_Concept
management	I-General_Concept
unit	I-General_Concept
(	O
IOMMU	B-General_Concept
)	O
.	O
</s>
<s>
,	O
64-bit	B-Device
architectures	I-Device
for	O
which	O
processors	O
are	O
being	O
manufactured	O
include	O
:	O
</s>
<s>
The	O
64-bit	B-Device
extension	O
created	O
by	O
Advanced	O
Micro	O
Devices	O
(	O
AMD	O
)	O
to	O
Intel	O
's	O
x86	B-Operating_System
architecture	I-Operating_System
(	O
later	O
licensed	O
by	O
Intel	O
)	O
;	O
commonly	O
termed	O
x86-64	B-Device
,	O
AMD64	B-Device
,	O
or	O
x64	B-Device
:	O
</s>
<s>
IBM	O
's	O
PowerPC/Power	O
ISA	O
:	O
</s>
<s>
SPARC	B-Architecture
V9	I-Architecture
architecture	O
:	O
</s>
<s>
IBM	O
's	O
z/Architecture	B-Device
,	O
a	O
64-bit	B-Device
version	O
of	O
the	O
ESA/390	O
architecture	O
,	O
used	O
in	O
IBM	O
's	O
eServer	B-Device
zSeries	I-Device
and	I-Device
System	I-Device
z	I-Device
mainframes	B-Device
:	O
</s>
<s>
Intel	O
's	O
IA-64	B-General_Concept
architecture	O
:	O
</s>
<s>
Elbrus	B-Device
architecture	O
:	O
</s>
<s>
Most	O
architectures	O
of	O
64	B-Device
bits	I-Device
that	O
are	O
derived	O
from	O
the	O
same	O
architecture	O
of	O
32	O
bits	O
can	O
execute	O
code	O
written	O
for	O
the	O
32-bit	O
versions	O
natively	O
,	O
with	O
no	O
performance	O
penalty	O
.	O
</s>
