<s>
Virtual	O
DOS	B-Device
machines	O
(	O
VDM	O
)	O
refer	O
to	O
a	O
technology	O
that	O
allows	O
running	O
16-bit/32	O
-bit	O
DOS	B-Device
and	O
16-bit	B-Application
Windows	I-Application
programs	O
when	O
there	O
is	O
already	O
another	O
operating	B-General_Concept
system	I-General_Concept
running	O
and	O
controlling	O
the	O
hardware	O
.	O
</s>
<s>
Virtual	O
DOS	B-Device
machines	O
can	O
operate	O
either	O
exclusively	O
through	O
typical	O
software	B-Application
emulation	I-Application
methods	O
(	O
e.g.	O
</s>
<s>
dynamic	O
recompilation	O
)	O
or	O
can	O
rely	O
on	O
the	O
virtual	B-Application
8086	I-Application
mode	I-Application
of	O
the	O
Intel	B-General_Concept
80386	I-General_Concept
processor	O
,	O
which	O
allows	O
real	B-Application
mode	I-Application
8086	O
software	O
to	O
run	O
in	O
a	O
controlled	O
environment	O
by	O
catching	O
all	O
operations	O
which	O
involve	O
accessing	O
protected	O
hardware	O
and	O
forwarding	O
them	O
to	O
the	O
normal	O
operating	B-General_Concept
system	I-General_Concept
(	O
as	O
exceptions	O
)	O
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
can	O
then	O
perform	O
an	O
emulation	B-Application
and	O
resume	O
the	O
execution	O
of	O
the	O
DOS	B-Device
software	O
.	O
</s>
<s>
VDMs	O
generally	O
also	O
implement	O
support	O
for	O
running	O
16	B-Device
-	I-Device
and	O
32-bit	O
protected	B-Application
mode	I-Application
software	O
(	O
DOS	B-Device
extenders	I-Device
)	O
,	O
which	O
has	O
to	O
conform	O
to	O
the	O
DOS	B-Device
Protected	B-Application
Mode	I-Application
Interface	O
(	O
DPMI	O
)	O
.	O
</s>
<s>
When	O
a	O
DOS	B-Device
program	O
running	O
inside	O
a	O
VDM	O
needs	O
to	O
access	O
a	O
peripheral	O
,	O
Windows	B-Application
will	O
either	O
allow	O
this	O
directly	O
(	O
rarely	O
)	O
,	O
or	O
will	O
present	O
the	O
DOS	B-Device
program	O
with	O
a	O
virtual	O
device	O
driver	O
(	O
VDD	O
)	O
which	O
emulates	B-Application
the	O
hardware	O
using	O
operating	B-General_Concept
system	I-General_Concept
functions	O
.	O
</s>
<s>
A	O
VDM	O
will	O
systematically	O
have	O
emulations	B-Application
for	O
the	O
Intel	B-Device
8259A	I-Device
interrupt	B-Application
controllers	O
,	O
the	O
8254	B-Device
timer	O
chips	O
,	O
the	O
8237	O
DMA	O
controller	O
,	O
etc	O
.	O
</s>
<s>
In	O
January	O
1985	O
Digital	O
Research	O
together	O
with	O
Intel	O
previewed	O
Concurrent	B-Operating_System
DOS	I-Operating_System
286	I-Operating_System
1.0	O
,	O
a	O
version	O
of	O
Concurrent	B-Operating_System
DOS	I-Operating_System
capable	O
of	O
running	O
real	B-Application
mode	I-Application
DOS	B-Device
programs	O
in	O
the	O
80286	B-General_Concept
's	O
protected	B-Application
mode	I-Application
.	O
</s>
<s>
Although	O
with	O
the	O
E-1	O
stepping	O
Intel	O
started	O
to	O
address	O
the	O
issues	O
in	O
August	O
1985	O
,	O
so	O
that	O
Digital	O
Research	O
's	O
"	O
8086	B-Operating_System
emulation	I-Operating_System
mode	I-Operating_System
"	O
worked	O
again	O
utilizing	O
the	O
undocumented	O
LOADALL	B-Device
processor	O
instruction	O
,	O
it	O
was	O
too	O
slow	O
to	O
be	O
practical	O
.	O
</s>
<s>
Microcode	B-Device
changes	O
for	O
the	O
E-2	O
stepping	O
improved	O
the	O
speed	O
again	O
.	O
</s>
<s>
This	O
early	O
implementation	O
can	O
be	O
seen	O
as	O
a	O
predecessor	O
to	O
actual	O
virtual	O
DOS	B-Device
machines	O
.	O
</s>
<s>
Eventually	O
,	O
Concurrent	B-Operating_System
DOS	I-Operating_System
286	I-Operating_System
was	O
reworked	O
from	O
a	O
potential	O
desktop	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
to	O
become	O
FlexOS	B-Operating_System
286	I-Operating_System
for	O
industrial	O
use	O
in	O
1986	O
.	O
</s>
<s>
When	O
Intel	O
's	O
80386	B-General_Concept
with	O
its	O
virtual	B-Application
8086	I-Application
mode	I-Application
became	O
available	O
(	O
as	O
samples	O
since	O
October	O
1985	O
and	O
in	O
quantities	O
since	O
June	O
1986	O
)	O
,	O
Digital	O
Research	O
switched	O
to	O
use	O
this	O
to	O
run	O
real	B-Application
mode	I-Application
DOS	B-Device
programs	O
in	O
virtual	O
DOS	B-Device
machines	O
in	O
protected	B-Application
mode	I-Application
under	O
Concurrent	B-Operating_System
DOS	I-Operating_System
386	I-Operating_System
1.0	O
(	O
February	O
1987	O
)	O
and	O
FlexOS	B-Operating_System
386	I-Operating_System
1.0	I-Operating_System
(	O
June	O
1987	O
)	O
.	O
</s>
<s>
protected	B-Application
mode	I-Application
operating	B-General_Concept
systems	I-General_Concept
was	O
not	O
DOS-based	O
by	O
themselves	O
.	O
</s>
<s>
Concurrent	B-Operating_System
DOS	I-Operating_System
386	I-Operating_System
was	O
later	O
developed	O
to	O
become	O
Multiuser	B-Operating_System
DOS	I-Operating_System
(	O
since	O
1991	O
)	O
and	O
REAL/32	B-Operating_System
(	O
since	O
1995	O
)	O
.	O
</s>
<s>
FlexOS	B-Operating_System
386	I-Operating_System
later	O
became	O
4690	B-Language
OS	I-Language
in	O
1993	O
.	O
</s>
<s>
In	O
contrast	O
to	O
these	O
protected	B-Application
mode	I-Application
operating	B-General_Concept
systems	I-General_Concept
,	O
DOS	B-Device
,	O
by	O
default	O
,	O
is	O
a	O
real-mode	B-Application
operating	B-General_Concept
system	I-General_Concept
,	O
switching	O
to	O
protected	B-Application
mode	I-Application
and	O
virtual	O
86	O
mode	O
only	O
on	O
behalf	O
of	O
memory	O
managers	O
and	O
DOS	B-Device
extenders	I-Device
in	O
order	O
to	O
provide	O
access	O
to	O
extended	O
memory	O
or	O
map	O
in	O
memory	O
into	O
the	O
first	O
megabyte	O
,	O
which	O
is	O
accessible	O
to	O
normal	O
DOS	B-Device
programs	O
.	O
</s>
<s>
DOS-based	O
VDMs	O
appeared	O
with	O
Microsoft	O
's	O
Windows/386	O
2.01	O
in	O
September	O
1987	O
.	O
</s>
<s>
DOS-based	O
virtual	O
DOS	B-Device
machines	O
were	O
also	O
present	O
in	O
Windows	B-Application
3.0	I-Application
,	O
3.1x	B-Application
and	O
Windows	B-Application
for	O
Workgroups	O
3.1x	B-Application
running	O
in	O
386	B-General_Concept
Enhanced	O
Mode	O
as	O
well	O
as	O
in	O
Windows	B-Application
95	I-Application
,	O
98	B-Device
,	O
98	B-Device
SE	O
and	O
ME	B-Device
.	O
</s>
<s>
One	O
of	O
the	O
characteristics	O
of	O
these	O
solutions	O
running	O
on	O
top	O
of	O
DOS	B-Device
is	O
that	O
the	O
memory	O
layout	O
shown	O
inside	O
virtual	O
DOS	B-Device
machines	O
are	O
virtual	O
instances	O
of	O
the	O
DOS	B-Device
system	B-Application
and	O
DOS	B-Device
driver	O
configuration	O
run	O
before	O
the	O
multitasker	O
is	O
loaded	O
,	O
and	O
that	O
requests	O
which	O
cannot	O
be	O
handled	O
in	O
protected	B-Application
mode	I-Application
are	O
passed	O
down	O
into	O
the	O
system	B-Application
domain	O
to	O
be	O
executed	O
by	O
the	O
underlying	O
DOS	B-Device
system	B-Application
.	O
</s>
<s>
Similar	O
to	O
Windows	B-Application
3.x	I-Application
386	B-General_Concept
Enhanced	O
Mode	O
in	O
architecture	O
,	O
EMM386	B-Device
3.xx	O
of	O
Novell	O
DOS	B-Device
7	O
,	O
Caldera	O
OpenDOS	O
7.01	O
,	O
DR-DOS	O
7.02	O
(	O
and	O
later	O
)	O
also	O
uses	O
DOS-based	O
VDMs	O
to	O
support	O
pre-emptive	O
multitasking	O
of	O
multiple	O
DOS	B-Device
applications	O
,	O
when	O
the	O
EMM386	B-Device
/MULTI	O
option	O
is	O
used	O
.	O
</s>
<s>
This	O
component	O
has	O
been	O
under	O
development	O
at	O
Digital	O
Research	O
/	O
Novell	O
since	O
1991	O
under	O
the	O
codename	O
"	O
Vladivar	O
"	O
(	O
originally	O
a	O
separate	O
device	O
driver	O
KRNL386.SYS	O
instead	O
of	O
a	O
module	O
of	O
EMM386	B-Device
)	O
.	O
</s>
<s>
While	O
primarily	O
developed	O
for	O
the	O
next	O
major	O
version	O
of	O
DRDOS	O
,	O
released	O
as	O
Novell	O
DOS	B-Device
7	O
in	O
1994	O
,	O
it	O
was	O
also	O
used	O
in	O
the	O
never	O
released	O
DR	O
DOS	B-Device
"	O
Panther	O
"	O
and	O
"	O
Star	B-Operating_System
Trek	I-Operating_System
"	O
project	O
in	O
1992/1993	O
.	O
</s>
<s>
Multiple	O
virtual	O
DOS	B-Device
machines	O
(	O
MVDM	O
)	O
are	O
used	O
in	O
OS/2	O
2.0	O
and	O
later	O
since	O
1992	O
.	O
</s>
<s>
For	O
example	O
,	O
block	O
devices	O
are	O
supported	O
,	O
and	O
various	O
DOS	B-Device
versions	O
can	O
be	O
booted	O
into	O
an	O
OS/2	O
MVDM	O
.	O
</s>
<s>
While	O
the	O
OS/2	O
1.x	O
DOS	B-Application
box	I-Application
was	O
based	O
on	O
DOS	B-Device
3.0	O
,	O
OS/2	O
2.x	O
MVDMs	O
emulate	O
DOS	B-Device
5.0	O
.	O
</s>
<s>
Seamless	O
integration	O
of	O
Windows	B-Application
3.1	I-Application
and	O
later	O
Win32s	B-Library
applications	O
in	O
OS/2	O
is	O
a	O
concept	O
looking	O
similar	O
on	O
surface	O
to	O
the	O
seamless	O
integration	O
of	O
XP	B-Application
Mode	O
based	O
on	O
Windows	B-Application
Virtual	I-Application
PC	I-Application
in	O
Windows	B-Device
7	I-Device
.	O
</s>
<s>
Applications	O
in	O
a	O
"	O
guest	O
"	O
can	O
use	O
named	B-Operating_System
pipes	I-Operating_System
for	O
communication	O
with	O
their	O
"	O
host	O
"	O
.	O
</s>
<s>
Due	O
to	O
a	O
technical	O
limitation	O
,	O
DOS	B-Device
and	O
16-bit	B-Application
Windows	I-Application
applications	O
under	O
OS/2	O
were	O
unable	O
to	O
see	O
more	O
than	O
2GB	O
of	O
hard	O
drive	O
space	O
;	O
this	O
was	O
fixed	O
in	O
ArcaOS	B-Device
5.0.4	I-Device
.	O
</s>
<s>
NTVDM	O
was	O
a	O
system	B-Application
component	O
of	O
all	O
IA-32	B-Device
editions	O
of	O
the	O
Windows	B-Device
NT	I-Device
family	I-Device
since	O
1993	O
with	O
the	O
release	O
of	O
Windows	B-Device
NT	I-Device
3.1	I-Device
.	O
</s>
<s>
It	O
allows	O
execution	O
of	O
16-bit	B-Application
Windows	I-Application
and	O
16-bit	B-Device
/	O
32-bit	O
DOS	B-Device
applications	O
.	O
</s>
<s>
The	O
Windows	B-Device
NT	I-Device
32-bit	O
user-mode	O
executable	O
which	O
forms	O
the	O
basis	O
for	O
a	O
single	O
DOS	B-Device
(	O
or	O
Windows	B-Application
3.x	I-Application
)	O
environment	O
is	O
called	O
.	O
</s>
<s>
In	O
order	O
to	O
execute	O
DOS	B-Device
programs	O
,	O
NTVDM	O
loads	O
which	O
in	O
turn	O
loads	O
,	O
which	O
executes	O
a	O
modified	O
in	O
order	O
to	O
run	O
the	O
application	O
that	O
was	O
passed	O
to	O
NTVDM	O
as	O
command-line	O
argument	O
.	O
</s>
<s>
The	O
16-bit	B-Device
real-mode	B-Application
system	B-Application
files	O
are	O
stripped	O
down	O
derivations	O
of	O
their	O
MS-DOS	O
5.0	O
equivalents	O
,	O
and	O
with	O
all	O
hard-wired	O
assumptions	O
on	O
the	O
FAT	B-Application
file	I-Application
system	I-Application
removed	O
and	O
using	O
the	O
invalid	B-Language
opcode	I-Language
0xC40xC4	O
to	O
bop	O
down	O
into	O
the	O
32-bit	O
NTVDM	O
to	O
handle	O
the	O
requests	O
.	O
</s>
<s>
Originally	O
,	O
NTDOS	O
reported	O
a	O
DOS	B-Device
version	O
of	O
30.00	O
to	O
programs	O
,	O
but	O
this	O
was	O
soon	O
changed	O
to	O
report	O
a	O
version	O
of	O
5.00	O
at	O
and	O
5.50	O
at	O
to	O
allow	O
more	O
programs	O
to	O
run	O
unmodified	O
.	O
</s>
<s>
This	O
holds	O
true	O
even	O
in	O
the	O
newest	O
releases	O
of	O
Windows	B-Application
;	O
many	O
additional	O
MS-DOS	O
functions	O
and	O
commands	B-Application
introduced	O
in	O
MS-DOS	O
versions	O
6.x	O
and	O
in	O
Windows	B-Application
9x	O
are	O
missing	O
.	O
</s>
<s>
16-bit	B-Application
Windows	I-Application
applications	O
by	O
default	O
all	O
run	O
in	O
their	O
own	O
thread	O
within	O
a	O
single	O
NTVDM	O
process	O
.	O
</s>
<s>
Although	O
NTVDM	O
itself	O
is	O
a	O
32-bit	O
process	O
and	O
pre-emptively	O
multitasked	O
with	O
respect	O
to	O
the	O
rest	O
of	O
the	O
system	B-Application
,	O
the	O
16-bit	B-Device
applications	O
within	O
it	O
are	O
cooperatively	O
multitasked	O
with	O
respect	O
to	O
each	O
other	O
.	O
</s>
<s>
When	O
the	O
"	O
Run	O
in	O
separate	O
memory	O
space	O
"	O
option	O
is	O
checked	O
in	O
the	O
Run	O
box	O
or	O
the	O
application	O
's	O
shortcut	O
file	O
,	O
each	O
16-bit	B-Application
Windows	I-Application
application	O
gets	O
its	O
own	O
NTVDM	O
process	O
and	O
is	O
therefore	O
pre-emptively	O
multitasked	O
with	O
respect	O
to	O
other	O
processes	O
,	O
including	O
other	O
16-bit	B-Application
Windows	I-Application
applications	O
.	O
</s>
<s>
NTVDM	O
emulates	B-Application
BIOS	O
calls	O
and	O
tables	O
as	O
well	O
as	O
the	O
Windows	B-Application
3.1	I-Application
kernel	O
and	O
16-bit	B-Device
API	O
stubs	O
.	O
</s>
<s>
The	O
32-bit	O
WoW	B-Application
translation	O
layer	O
thunks	B-Application
16-bit	B-Device
API	O
routines	O
.	O
</s>
<s>
32-bit	O
DOS	B-Device
emulation	B-Application
is	O
present	O
for	O
DOS	B-Device
Protected	B-Application
Mode	I-Application
Interface	O
(	O
DPMI	O
)	O
and	O
32-bit	O
memory	O
access	O
.	O
</s>
<s>
This	O
layer	O
converts	O
the	O
necessary	O
extended	O
and	O
expanded	O
memory	O
calls	O
for	O
DOS	B-Device
functions	O
into	O
Windows	B-Device
NT	I-Device
memory	O
calls	O
.	O
</s>
<s>
is	O
the	O
emulation	B-Application
layer	O
that	O
emulates	B-Application
16-bit	B-Application
Windows	I-Application
.	O
</s>
<s>
Windows	B-Application
2000	I-Application
and	O
Windows	B-Application
XP	I-Application
added	O
Sound	B-Application
Blaster	I-Application
2.0	O
emulation	B-Application
.	O
</s>
<s>
16-bit	B-Device
virtual	O
device	O
drivers	O
and	O
DOS	B-Device
block	O
device	O
drivers	O
(	O
e.g.	O
,	O
RAM	O
disks	O
)	O
are	O
not	O
supported	O
.	O
</s>
<s>
Inter-process	B-Operating_System
communication	I-Operating_System
with	O
other	O
subsystems	O
can	O
take	O
place	O
through	O
OLE	B-Operating_System
,	O
DDE	B-Operating_System
and	O
named	B-Operating_System
pipes	I-Operating_System
.	O
</s>
<s>
Since	O
virtual	B-Application
8086	I-Application
mode	I-Application
is	O
not	O
available	O
on	O
non-x86-based	O
processors	O
(	O
more	O
specifically	O
,	O
MIPS	B-Device
,	O
DEC	B-Device
Alpha	I-Device
,	O
and	O
PowerPC	B-Architecture
)	O
NTVDM	O
was	O
instead	O
implemented	O
as	O
a	O
full	O
emulator	B-Application
in	O
these	O
versions	O
of	O
NT	O
,	O
using	O
code	O
licensed	O
from	O
Insignia	O
's	O
SoftPC	B-Device
.	O
</s>
<s>
Up	O
to	O
Windows	B-Device
NT	I-Device
3.51	I-Device
,	O
only	O
80286	B-General_Concept
emulation	B-Application
was	O
available	O
.	O
</s>
<s>
With	O
Windows	B-Device
NT	I-Device
4.0	I-Device
,	O
486	B-General_Concept
emulation	B-Application
was	O
added	O
.	O
</s>
<s>
NTVDM	O
is	O
not	O
included	O
with	O
64-bit	O
versions	O
of	O
Windows	B-Application
or	O
ARM32	O
based	O
versions	O
such	O
as	O
Windows	B-Operating_System
RT	I-Operating_System
or	O
Windows	B-Operating_System
10	I-Operating_System
IoT	O
Core	O
.	O
</s>
<s>
Windows	B-Operating_System
10	I-Operating_System
is	O
the	O
final	O
version	O
of	O
Windows	B-Application
to	O
include	O
this	O
component	O
.	O
</s>
<s>
This	O
component	O
has	O
since	O
been	O
discontinued	O
,	O
as	O
Windows	B-Application
11	O
dropped	O
support	O
for	O
32-bit	O
processors	O
.	O
</s>
<s>
The	O
following	O
list	O
of	O
commands	B-Application
is	O
part	O
of	O
the	O
Windows	B-Application
XP	I-Application
MS-DOS	O
subsystem	O
.	O
</s>
<s>
In	O
January	O
2010	O
,	O
Google	B-Application
security	O
researcher	O
Tavis	O
Ormandy	O
revealed	O
a	O
serious	O
security	O
flaw	O
in	O
Windows	B-Device
NT	I-Device
's	O
VDM	O
implementation	O
that	O
allowed	O
unprivileged	O
users	O
to	O
escalate	O
their	O
privileges	O
to	O
SYSTEM	B-Application
level	O
,	O
noted	O
as	O
applicable	O
to	O
the	O
security	O
of	O
all	O
x86	B-Operating_System
versions	O
of	O
the	O
Windows	B-Device
NT	I-Device
kernel	O
since	O
1993	O
.	O
</s>
<s>
This	O
included	O
all	O
32-bit	O
versions	O
of	O
Windows	B-Device
NT	I-Device
,	O
2000	O
,	O
XP	B-Application
,	O
Server	O
2003	O
,	O
Vista	O
,	O
Server	O
2008	O
,	O
and	O
Windows	B-Device
7	I-Device
.	O
</s>
<s>
Prior	O
to	O
Microsoft	O
's	O
release	O
of	O
a	O
security	O
patch	O
,	O
the	O
workaround	O
for	O
this	O
issue	O
was	O
to	O
turn	O
off	O
16-bit	B-Device
application	O
support	O
,	O
which	O
prevented	O
older	O
programs	O
(	O
those	O
written	O
for	O
DOS	B-Device
and	O
Windows	B-Application
3.1	I-Application
)	O
from	O
running	O
.	O
</s>
<s>
64-bit	O
versions	O
of	O
Windows	B-Application
are	O
not	O
affected	O
since	O
the	O
NTVDM	O
subsystem	O
is	O
not	O
included	O
.	O
</s>
<s>
Once	O
the	O
Microsoft	O
security	O
patches	O
had	O
been	O
applied	O
to	O
the	O
affected	O
operating	B-General_Concept
systems	I-General_Concept
the	O
VDM	O
could	O
be	O
safely	O
reenabled	O
.	O
</s>
<s>
A	O
limitation	O
exists	O
in	O
the	O
Windows	B-Application
XP	I-Application
16-bit	B-Device
subsystem	O
(	O
but	O
not	O
in	O
earlier	O
versions	O
of	O
Windows	B-Device
NT	I-Device
)	O
because	O
of	O
the	O
raised	O
per-session	O
limit	O
for	O
GDI	O
objects	O
which	O
causes	O
GDI	O
handles	O
to	O
be	O
shifted	O
to	O
the	O
right	O
by	O
two	O
bits	O
,	O
when	O
converting	O
them	O
from	O
32	O
to	O
16	B-Device
bits	I-Device
.	O
</s>
<s>
As	O
a	O
result	O
,	O
the	O
actual	O
handle	O
cannot	O
be	O
larger	O
than	O
14	O
bits	O
and	O
consequently	O
16-bit	B-Device
applications	O
that	O
happen	O
to	O
be	O
served	O
a	O
handle	O
larger	O
than	O
16384	O
by	O
the	O
GDI	O
system	B-Application
crash	O
and	O
terminate	O
with	O
an	O
error	O
message	O
.	O
</s>
<s>
In	O
general	O
,	O
VDM	O
and	O
similar	O
technologies	O
do	O
not	O
satisfactorily	O
run	O
most	O
older	O
DOS	B-Device
games	O
on	O
today	O
's	O
computers	O
.	O
</s>
<s>
Emulation	B-Application
is	O
only	O
provided	O
for	O
the	O
most	O
basic	O
peripherals	O
,	O
often	O
implemented	O
incompletely	O
.	O
</s>
<s>
For	O
example	O
,	O
sound	O
emulation	B-Application
in	O
NTVDM	O
is	O
very	O
limited	O
.	O
</s>
<s>
NT-family	O
versions	O
of	O
Windows	B-Application
only	O
update	O
the	O
real	O
screen	O
a	O
few	O
times	O
per	O
second	O
when	O
a	O
DOS	B-Device
program	O
writes	O
to	O
it	O
,	O
and	O
they	O
do	O
not	O
emulate	O
higher	O
resolution	O
graphics	O
modes	O
.	O
</s>
<s>
This	O
either	O
makes	O
a	O
game	O
run	O
much	O
too	O
fast	O
or	O
causes	O
the	O
software	O
not	O
even	O
to	O
notice	O
the	O
emulated	B-Application
hardware	O
peripherals	O
,	O
because	O
it	O
does	O
not	O
wait	O
long	O
enough	O
for	O
an	O
answer	O
.	O
</s>
<s>
In	O
an	O
x86-64	B-Device
CPU	O
,	O
virtual	B-Application
8086	I-Application
mode	I-Application
is	O
available	O
as	O
a	O
sub-mode	O
only	O
in	O
its	O
legacy	O
mode	O
(	O
for	O
running	O
16	B-Device
-	I-Device
and	O
32-bit	O
operating	B-General_Concept
systems	I-General_Concept
)	O
,	O
not	O
in	O
the	O
native	O
64-bit	O
long	B-Application
mode	I-Application
.	O
</s>
<s>
NTVDM	O
is	O
not	O
supported	O
on	O
x86-64	B-Device
editions	O
of	O
Windows	B-Application
,	O
including	O
DOS	B-Device
programs	O
,	O
because	O
NTVDM	O
uses	O
VM86	B-Application
CPU	O
mode	O
instead	O
of	O
the	O
Local	O
Descriptor	O
Table	O
in	O
order	O
to	O
enable	O
16‑bits	O
segment	O
required	O
for	O
addressing	O
.	O
</s>
<s>
NTVDM	O
is	O
also	O
unavailable	O
on	O
AArch64	B-Architecture
versions	O
of	O
Windows	B-Application
(	O
such	O
as	O
Windows	B-Operating_System
RT	I-Operating_System
)	O
,	O
because	O
Microsoft	O
did	O
not	O
release	O
a	O
full	O
emulator	B-Application
for	O
this	O
incompatible	O
instruction	O
set	O
like	O
it	O
did	O
on	O
previous	O
incompatible	O
architectures	O
.	O
</s>
<s>
Whilst	O
NTVDM	O
is	O
not	O
supported	O
on	O
x86-64	B-Device
and	O
AArch64	B-Architecture
versions	O
of	O
Windows	B-Application
,	O
they	O
can	O
still	O
be	O
run	O
using	O
virtualization	B-General_Concept
software	O
,	O
such	O
as	O
Windows	B-Application
XP	I-Application
Mode	O
in	O
non-home	O
versions	O
of	O
Windows	B-Device
7	I-Device
or	O
VMware	B-Operating_System
Workstation	I-Operating_System
.	O
</s>
<s>
Other	O
methods	O
include	O
using	O
NTVDMx64	O
,	O
an	O
unofficial	O
port	O
of	O
the	O
leaked	O
emulated	B-Application
implementation	O
of	O
NTVDM	O
from	O
Windows	B-Device
NT	I-Device
4.0	I-Device
for	O
non-x86	O
platforms	O
,	O
or	O
OTVDM	O
(	O
WineVDM	O
)	O
,	O
a	O
16-bit	B-Application
Windows	I-Application
interpreter	O
based	O
on	O
MAME	B-Device
's	O
i386	B-General_Concept
emulation	B-Application
and	O
the	O
16-bit	B-Device
portion	O
of	O
the	O
popular	O
Windows	B-Application
compatibility	O
layer	O
,	O
Wine	B-Application
.	O
</s>
