<s>
A	O
control	B-Operating_System
register	I-Operating_System
is	O
a	O
processor	B-General_Concept
register	I-General_Concept
which	O
changes	O
or	O
controls	O
the	O
general	O
behavior	O
of	O
a	O
CPU	B-General_Concept
or	O
other	O
digital	O
device	O
.	O
</s>
<s>
Common	O
tasks	O
performed	O
by	O
control	B-Operating_System
registers	I-Operating_System
include	O
interrupt	B-Application
control	O
,	O
switching	O
the	O
addressing	B-Language
mode	I-Language
,	O
paging	B-Architecture
control	O
,	O
and	O
coprocessor	B-General_Concept
control	O
.	O
</s>
<s>
The	O
CR0	B-Operating_System
register	O
is	O
32	O
bits	O
long	O
on	O
the	O
386	B-General_Concept
and	O
higher	O
processors	O
.	O
</s>
<s>
On	O
x64	B-Device
processors	O
in	O
long	B-Application
mode	I-Application
,	O
it	O
(	O
and	O
the	O
other	O
control	B-Operating_System
registers	I-Operating_System
)	O
is	O
64	O
bits	O
long	O
.	O
</s>
<s>
CR0	B-Operating_System
has	O
various	O
control	O
flags	B-General_Concept
that	O
modify	O
the	O
basic	O
operation	O
of	O
the	O
processor	O
.	O
</s>
<s>
Register	O
CR0	B-Operating_System
is	O
the	O
32	O
Bit	O
version	O
of	O
the	O
old	O
Machine	O
Status	O
Word	O
(	O
MSW	O
)	O
register	O
.	O
</s>
<s>
The	O
MSW	O
register	O
was	O
expanded	O
to	O
the	O
Control	B-Operating_System
Register	I-Operating_System
with	O
the	O
appearance	O
of	O
the	O
i386	B-General_Concept
processor	O
.	O
</s>
<s>
Bit	O
Name	O
Full	O
Name	O
Description	O
0	O
PE	O
Protected	B-Application
Mode	I-Application
Enable	O
If	O
1	O
,	O
system	O
is	O
in	O
protected	B-Application
mode	I-Application
,	O
else	O
,	O
system	O
is	O
in	O
real	B-Application
mode	I-Application
1	O
MP	O
Monitor	O
co-processor	B-General_Concept
Controls	O
interaction	O
of	O
WAIT/FWAIT	O
instructions	O
with	O
TS	O
flag	O
in	O
CR0	B-Operating_System
2	O
EM	O
Emulation	O
If	O
set	O
,	O
no	O
x87	B-Application
floating-point	B-General_Concept
unit	I-General_Concept
present	O
,	O
if	O
clear	O
,	O
x87	B-Application
FPU	I-Application
present	O
3	O
TS	O
Task	O
switched	O
Allows	O
saving	O
x87	B-Application
task	O
context	O
upon	O
a	O
task	O
switch	O
only	O
after	O
x87	B-Application
instruction	O
used	O
4	O
ET	O
Extension	O
type	O
On	O
the	O
386	B-General_Concept
,	O
it	O
allowed	O
to	O
specify	O
whether	O
the	O
external	O
math	B-General_Concept
coprocessor	I-General_Concept
was	O
an	O
80287	O
or	O
80387	O
5	O
NE	O
Numeric	O
error	O
Enable	O
internal	O
x87	B-Application
floating	O
point	O
error	O
reporting	O
when	O
set	O
,	O
else	O
enables	O
PC	O
style	O
x87	B-Application
error	O
detection	O
16	O
WP	O
Write	O
protect	O
When	O
set	O
,	O
the	O
CPU	B-General_Concept
ca	O
n't	O
write	O
to	O
read-only	O
pages	O
when	O
privilege	O
level	O
is	O
0	O
18	O
AM	O
Alignment	O
mask	O
Alignment	O
check	O
enabled	O
if	O
AM	O
set	O
,	O
AC	O
flag	O
(	O
in	O
EFLAGS	B-General_Concept
register	I-General_Concept
)	O
set	O
,	O
and	O
privilege	O
level	O
is	O
3	O
29	O
NW	O
Not-write	O
through	O
Globally	O
enables/disable	O
write-through	O
caching	O
30	O
CD	O
Cache	B-General_Concept
disable	O
Globally	O
enables/disable	O
the	O
memory	O
cache	B-General_Concept
31	O
PG	O
Paging	B-Architecture
If	O
1	O
,	O
enable	O
paging	B-Architecture
and	O
use	O
the	O
register	O
,	O
else	O
disable	O
paging	B-Architecture
.	O
</s>
<s>
Reserved	O
,	O
the	O
CPU	B-General_Concept
will	O
throw	O
a	O
#UD	O
exception	O
when	O
trying	O
to	O
access	O
it	O
.	O
</s>
<s>
Contains	O
a	O
value	O
called	O
Page	O
Fault	B-Application
Linear	O
Address	O
(	O
PFLA	O
)	O
.	O
</s>
<s>
When	O
a	O
page	O
fault	B-Application
occurs	O
,	O
the	O
address	O
the	O
program	O
attempted	O
to	O
access	O
is	O
stored	O
in	O
the	O
CR2	O
register	O
.	O
</s>
<s>
Used	O
when	O
virtual	B-Architecture
addressing	I-Architecture
is	O
enabled	O
,	O
hence	O
when	O
the	O
PG	O
bit	O
is	O
set	O
in	O
CR0	B-Operating_System
.	O
</s>
<s>
CR3	O
enables	O
the	O
processor	O
to	O
translate	O
linear	O
addresses	O
into	O
physical	O
addresses	O
by	O
locating	O
the	O
page	O
directory	O
and	O
page	B-General_Concept
tables	I-General_Concept
for	O
the	O
current	O
task	O
.	O
</s>
<s>
Used	O
in	O
protected	B-Application
mode	I-Application
to	O
control	O
operations	O
such	O
as	O
virtual-8086	O
support	O
,	O
enabling	O
I/O	B-General_Concept
breakpoints	O
,	O
page	B-General_Concept
size	I-General_Concept
extension	I-General_Concept
and	O
machine-check	B-Device
exceptions	I-Device
.	O
</s>
<s>
Bit	O
Name	O
Full	O
Name	O
Description	O
0	O
VME	O
Virtual	O
8086	O
Mode	O
Extensions	O
If	O
set	O
,	O
enables	O
support	O
for	O
the	O
virtual	O
interrupt	B-Application
flag	O
(	O
VIF	O
)	O
in	O
virtual-8086	O
mode	O
.	O
</s>
<s>
1	O
PVI	O
Protected-mode	B-Application
Virtual	O
Interrupts	B-Application
If	O
set	O
,	O
enables	O
support	O
for	O
the	O
virtual	O
interrupt	B-Application
flag	O
(	O
VIF	O
)	O
in	O
protected	B-Application
mode	I-Application
.	O
</s>
<s>
2	O
TSD	O
Time	O
Stamp	O
Disable	O
If	O
set	O
,	O
RDTSC	B-Device
instruction	O
can	O
only	O
be	O
executed	O
when	O
in	O
ring	B-Operating_System
0	I-Operating_System
,	O
otherwise	O
RDTSC	B-Device
can	O
be	O
used	O
at	O
any	O
privilege	O
level	O
.	O
</s>
<s>
3	O
DE	O
Debugging	O
Extensions	O
If	O
set	O
,	O
enables	O
debug	B-Device
register	I-Device
based	O
breaks	O
on	O
I/O	B-General_Concept
space	O
access	O
.	O
</s>
<s>
4	O
PSE	O
Page	B-General_Concept
Size	I-General_Concept
Extension	I-General_Concept
If	O
set	O
,	O
enables	O
32-bit	O
paging	B-Architecture
mode	O
to	O
use	O
4	O
MiB	O
huge	O
pages	O
in	O
addition	O
to	O
4	O
KiB	O
pages	O
.	O
</s>
<s>
If	O
PAE	O
is	O
enabled	O
or	O
the	O
processor	O
is	O
in	O
x86-64	B-Device
long	B-Application
mode	I-Application
this	O
bit	O
is	O
ignored	O
.	O
</s>
<s>
5	O
PAE	O
Physical	B-General_Concept
Address	I-General_Concept
Extension	I-General_Concept
If	O
set	O
,	O
changes	O
page	B-General_Concept
table	I-General_Concept
layout	O
to	O
translate	O
32-bit	O
virtual	O
addresses	O
into	O
extended	O
36-bit	O
physical	O
addresses	O
.	O
</s>
<s>
6	O
MCE	O
Machine	B-Device
Check	I-Device
Exception	I-Device
If	O
set	O
,	O
enables	O
machine	B-Device
check	I-Device
interrupts	B-Application
to	O
occur	O
.	O
</s>
<s>
8	O
PCE	O
Performance-Monitoring	O
Counter	O
enable	O
If	O
set	O
,	O
RDPMC	O
can	O
be	O
executed	O
at	O
any	O
privilege	O
level	O
,	O
else	O
RDPMC	O
can	O
only	O
be	O
used	O
in	O
ring	B-Operating_System
0	I-Operating_System
.	O
</s>
<s>
9	O
OSFXSR	O
Operating	O
system	O
support	O
for	O
FXSAVE	O
and	O
FXRSTOR	O
instructions	O
If	O
set	O
,	O
enables	O
Streaming	B-General_Concept
SIMD	I-General_Concept
Extensions	I-General_Concept
(	O
SSE	O
)	O
instructions	O
and	O
fast	O
FPU	O
save	O
&	O
restore	O
.	O
</s>
<s>
11	O
UMIP	O
User-Mode	B-Operating_System
Instruction	O
Prevention	O
If	O
set	O
,	O
the	O
SGDT	O
,	O
SIDT	O
,	O
SLDT	O
,	O
SMSW	O
and	O
STR	O
instructions	O
cannot	O
be	O
executed	O
if	O
CPL	O
>	O
0	O
.	O
</s>
<s>
12	O
LA57	O
57-Bit	O
Linear	O
Addresses	O
If	O
set	O
,	O
enables	O
5-Level	O
Paging	B-Architecture
.	O
</s>
<s>
13	O
VMXE	O
Virtual	O
Machine	O
Extensions	O
Enable	O
see	O
Intel	O
VT-x	O
x86	B-Operating_System
virtualization	B-General_Concept
.	O
</s>
<s>
14	O
SMXE	O
Safer	B-Device
Mode	I-Device
Extensions	I-Device
Enable	O
see	O
Trusted	B-Device
Execution	I-Device
Technology	I-Device
(	O
TXT	O
)	O
15	O
16	O
FSGSBASE	O
FSGSBASE	O
Enable	O
If	O
set	O
,	O
enables	O
the	O
instructions	O
RDFSBASE	O
,	O
RDGSBASE	O
,	O
WRFSBASE	O
,	O
and	O
WRGSBASE	O
.	O
</s>
<s>
20	O
Supervisor	O
Mode	O
Execution	O
Protection	O
Enable	O
If	O
set	O
,	O
execution	O
of	O
code	O
in	O
a	O
higher	O
ring	B-Operating_System
generates	O
a	O
fault	B-Application
.	O
</s>
<s>
21	O
SMAP	O
Supervisor	B-Device
Mode	I-Device
Access	I-Device
Prevention	I-Device
Enable	O
If	O
set	O
,	O
access	O
of	O
data	O
in	O
a	O
higher	O
ring	B-Operating_System
generates	O
a	O
fault.22	O
PKE	O
Protection	O
Key	O
Enable	O
See	O
Intel	O
64	O
and	O
IA-32	O
Architectures	O
Software	O
Developer	O
’s	O
Manual	O
.	O
</s>
<s>
24	O
PKS	O
Enable	O
Protection	O
Keys	O
for	O
Supervisor-Mode	O
Pages	O
If	O
set	O
,	O
each	O
supervisor-mode	O
linear	O
address	O
is	O
associated	O
with	O
a	O
protection	O
key	O
when	O
4-level	O
or	O
5-level	O
paging	B-Architecture
is	O
in	O
use	O
.	O
</s>
<s>
25	O
UINTR	O
User	O
Interrupts	B-Application
Enable	O
If	O
set	O
,	O
enables	O
user-mode	B-Operating_System
inter-processor	O
interrupts	B-Application
and	O
their	O
associated	O
instructions	O
and	O
data	O
structures	O
.	O
</s>
<s>
Extended	O
Feature	O
Enable	O
Register	O
(	O
EFER	O
)	O
is	O
a	O
model-specific	B-General_Concept
register	I-General_Concept
added	O
in	O
the	O
AMD	B-Architecture
K6	I-Architecture
processor	O
,	O
to	O
allow	O
enabling	O
the	O
SYSCALL/SYSRET	O
instruction	O
,	O
and	O
later	O
for	O
entering	O
and	O
exiting	O
long	B-Application
mode	I-Application
.	O
</s>
<s>
This	O
register	O
becomes	O
architectural	O
in	O
AMD64	B-Device
and	O
has	O
been	O
adopted	O
by	O
Intel	O
as	O
IA32_EFER	O
.	O
</s>
<s>
CR8	O
is	O
used	O
to	O
prioritize	O
external	O
interrupts	B-Application
and	O
is	O
referred	O
to	O
as	O
the	O
task-priority	O
register	O
(	O
TPR	O
)	O
.	O
</s>
<s>
The	O
AMD64	B-Device
architecture	O
allows	O
software	O
to	O
define	O
up	O
to	O
15	O
external	O
interrupt-priority	O
classes	O
.	O
</s>
<s>
CR8	O
uses	O
the	O
four	O
low-order	O
bits	O
for	O
specifying	O
a	O
task	B-Operating_System
priority	I-Operating_System
and	O
the	O
remaining	O
60	O
bits	O
are	O
reserved	O
and	O
must	O
be	O
written	O
with	O
zeros	O
.	O
</s>
<s>
System	O
software	O
can	O
use	O
the	O
TPR	O
register	O
to	O
temporarily	O
block	O
low-priority	O
interrupts	B-Application
from	O
interrupting	B-Application
a	O
high-priority	O
task	O
.	O
</s>
<s>
This	O
is	O
accomplished	O
by	O
loading	O
TPR	O
with	O
a	O
value	O
corresponding	O
to	O
the	O
highest-priority	O
interrupt	B-Application
that	O
is	O
to	O
be	O
blocked	O
.	O
</s>
<s>
For	O
example	O
,	O
loading	O
TPR	O
with	O
a	O
value	O
of	O
9	O
(	O
1001b	O
)	O
blocks	O
all	O
interrupts	B-Application
with	O
a	O
priority	O
class	O
of	O
9	O
or	O
less	O
,	O
while	O
allowing	O
all	O
interrupts	B-Application
with	O
a	O
priority	O
class	O
of	O
10	O
or	O
more	O
to	O
be	O
recognized	O
.	O
</s>
<s>
Loading	O
TPR	O
with	O
0	O
enables	O
all	O
external	O
interrupts	B-Application
.	O
</s>
<s>
Loading	O
TPR	O
with	O
15	O
(	O
1111b	O
)	O
disables	O
all	O
external	O
interrupts	B-Application
.	O
</s>
<s>
XCR0	O
,	O
or	O
Extended	O
Control	B-Operating_System
Register	I-Operating_System
0	O
,	O
is	O
a	O
control	B-Operating_System
register	I-Operating_System
which	O
is	O
used	O
to	O
toggle	O
the	O
storing	O
or	O
loading	O
of	O
registers	O
related	O
to	O
specific	O
CPU	B-General_Concept
features	O
using	O
the	O
XSAVE/XRSTOR	O
instructions	O
.	O
</s>
<s>
Bit	O
Purpose	O
0	O
X87	B-Application
(	O
x87	B-Application
FPU/MMX	O
State	O
,	O
note	O
,	O
must	O
be	O
'	O
1	O
 '	O
)	O
1	O
SSE	O
(	O
XSAVE	O
feature	O
set	O
enable	O
for	O
MXCSR	O
and	O
XMM	O
regs	O
)	O
2	O
AVX	O
(	O
AVX	O
enable	O
,	O
and	O
XSAVE	O
feature	O
set	O
can	O
be	O
used	O
to	O
manage	O
YMM	O
regs	O
)	O
3	O
BNDREG	O
(	O
MPX	O
enable	O
,	O
and	O
XSAVE	O
feature	O
set	O
can	O
be	O
used	O
for	O
BND	O
regs	O
)	O
4	O
BNDCSR	O
(	O
MPX	O
enable	O
,	O
and	O
XSAVE	O
feature	O
set	O
can	O
be	O
used	O
for	O
BNDCFGU	O
and	O
BNDSTATUS	O
regs	O
)	O
5	O
opmask	O
(	O
AVX-512	O
enable	O
,	O
and	O
XSAVE	O
feature	O
set	O
can	O
be	O
used	O
for	O
AVX	O
opmask	O
,	O
AKA	O
k-mask	O
,	O
regs	O
)	O
6	O
ZMM_hi256	O
(	O
AVX-512	O
enable	O
,	O
and	O
XSAVE	O
feature	O
set	O
can	O
be	O
used	O
for	O
upper-halves	O
of	O
the	O
lower	O
ZMM	O
regs	O
)	O
7	O
Hi16_ZMM	O
(	O
AVX-512	O
enable	O
,	O
and	O
XSAVE	O
feature	O
set	O
can	O
be	O
used	O
for	O
the	O
upper	O
ZMM	O
regs	O
)	O
8	O
Reserved	O
9	O
PKRU	O
(	O
XSAVE	O
feature	O
set	O
can	O
be	O
used	O
for	O
PKRU	O
register	O
,	O
which	O
is	O
part	O
of	O
the	O
protection	O
keys	O
mechanism	O
.	O
</s>
<s>
Put	O
simply	O
,	O
if	O
the	O
X87	B-Application
state	O
was	O
enabled	O
in	O
XCR0	O
and	O
PT	O
state	O
was	O
enabled	O
in	O
IA32_XSS	O
,	O
the	O
XSAVE	O
instruction	O
would	O
only	O
store	O
X87	B-Application
state	O
,	O
while	O
the	O
privileged	O
XSAVES	O
would	O
store	O
both	O
X87	B-Application
and	O
PT	O
states	O
.	O
</s>
<s>
Because	O
it	O
is	O
an	O
MSR	O
,	O
it	O
can	O
be	O
accessed	O
using	O
the	O
RDMSR	B-General_Concept
and	O
WRMSR	B-General_Concept
instructions	O
.	O
</s>
<s>
14	O
User	O
interrupts	B-Application
(	O
UINTR	O
)	O
state	O
15	O
Last	O
branch	O
recording	O
(	O
LBR	O
)	O
state	O
16	O
HWP	O
(	O
enables	O
the	O
saving/loading	O
of	O
IA32_HWP_REQUEST	O
MSR	O
)	O
17	O
–	O
63	O
Reserved	O
;	O
must	O
be	O
0	O
.	O
</s>
