<s>
OpenVMS	O
,	O
often	O
referred	O
to	O
as	O
just	O
VMS	O
,	O
is	O
a	O
multi-user	B-Operating_System
,	O
multiprocessing	B-Operating_System
and	O
virtual	O
memory-based	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
It	O
is	O
designed	O
to	O
support	O
time-sharing	B-General_Concept
,	O
batch	B-General_Concept
processing	I-General_Concept
,	O
transaction	B-General_Concept
processing	I-General_Concept
and	O
workstation	B-Device
applications	O
.	O
</s>
<s>
It	O
was	O
first	O
announced	O
by	O
Digital	O
Equipment	O
Corporation	O
(	O
DEC	O
)	O
as	O
VAX/VMS	O
(	O
Virtual	B-General_Concept
Address	I-General_Concept
eXtension/Virtual	O
Memory	O
System	O
)	O
alongside	O
the	O
VAX-11/780	O
minicomputer	B-Architecture
in	O
1977	O
.	O
</s>
<s>
OpenVMS	O
has	O
subsequently	O
been	O
ported	O
to	O
run	O
on	O
DEC	B-Device
Alpha	I-Device
systems	O
,	O
the	O
Itanium-based	O
HPE	B-General_Concept
Integrity	I-General_Concept
Servers	I-General_Concept
,	O
and	O
select	O
x86-64	B-Device
hardware	O
and	O
hypervisors	B-Operating_System
.	O
</s>
<s>
OpenVMS	O
offers	O
high	O
availability	O
through	O
clustering	B-Architecture
—	O
the	O
ability	O
to	O
distribute	O
the	O
system	O
over	O
multiple	O
physical	O
machines	O
.	O
</s>
<s>
This	O
allows	O
clustered	O
applications	O
and	O
data	O
to	O
remain	O
continuously	O
available	O
while	O
operating	B-General_Concept
system	I-General_Concept
software	O
and	O
hardware	O
maintenance	O
and	O
upgrades	O
are	O
performed	O
,	O
or	O
if	O
part	O
of	O
the	O
cluster	O
is	O
destroyed	O
.	O
</s>
<s>
In	O
April	O
1975	O
,	O
Digital	O
Equipment	O
Corporation	O
embarked	O
on	O
a	O
project	O
to	O
design	O
a	O
32-bit	O
extension	O
to	O
its	O
PDP-11	B-Device
computer	O
line	O
.	O
</s>
<s>
The	O
hardware	O
component	O
was	O
code	O
named	O
Star	O
;	O
the	O
operating	B-General_Concept
system	I-General_Concept
was	O
code	O
named	O
Starlet	O
.	O
</s>
<s>
The	O
Star	O
and	O
Starlet	O
projects	O
culminated	O
in	O
the	O
VAX-11/780	O
computer	O
and	O
the	O
VAX/VMS	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
VMS	O
was	O
mostly	O
written	O
in	O
VAX	B-Language
MACRO	I-Language
with	O
some	O
components	O
written	O
in	O
BLISS	B-Language
.	O
</s>
<s>
One	O
of	O
the	O
original	O
goals	O
for	O
VMS	O
was	O
backwards	B-General_Concept
compatibility	I-General_Concept
with	O
DEC	O
's	O
existing	O
RSX-11M	B-Application
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Prior	O
to	O
the	O
V3.0	O
release	O
,	O
VAX/VMS	O
included	O
an	O
compatibility	O
layer	O
named	O
the	O
RSX	O
Application	O
Migration	O
Executive	O
(	O
RSX	O
AME	O
)	O
which	O
allowed	O
user	O
mode	O
RSX-11M	B-Application
software	O
to	O
be	O
run	O
unmodified	O
on	O
top	O
of	O
VMS	O
.	O
</s>
<s>
The	O
RSX	O
AME	O
played	O
an	O
important	O
role	O
on	O
early	O
versions	O
of	O
VAX/VMS	O
,	O
which	O
used	O
re-used	O
certain	O
RSX-11M	B-Application
user	O
mode	O
utilities	O
before	O
native	O
VAX	B-Device
versions	O
had	O
been	O
developed	O
.	O
</s>
<s>
In	O
VAX/VMS	O
V4.0	O
,	O
RSX	O
AME	O
was	O
removed	O
from	O
the	O
base	O
system	O
,	O
and	O
replaced	O
with	O
an	O
optional	O
layered	O
product	O
named	O
VAX-11	O
RSX	O
.	O
</s>
<s>
A	O
number	O
of	O
distributions	O
of	O
VAX/VMS	O
were	O
created	O
:	O
</s>
<s>
MicroVMS	O
was	O
a	O
distribution	O
of	O
VAX/VMS	O
designed	O
for	O
MicroVAX	B-Device
and	O
VAXstation	B-Device
hardware	O
,	O
which	O
had	O
less	O
memory	O
and	O
disk	O
space	O
than	O
larger	O
VAX	B-Device
systems	O
of	O
the	O
time	O
.	O
</s>
<s>
MicroVMS	O
split	O
up	O
VAX/VMS	O
into	O
multiple	O
kits	O
,	O
which	O
a	O
customer	O
could	O
use	O
to	O
install	O
a	O
subset	O
of	O
VAX/VMS	O
tailored	O
to	O
their	O
specific	O
requirements	O
.	O
</s>
<s>
MicroVMS	O
releases	O
were	O
produced	O
for	O
each	O
of	O
the	O
V4.x	O
releases	O
of	O
VAX/VMS	O
and	O
was	O
discontinued	O
when	O
VAX/VMS	O
V5.0	O
was	O
released	O
.	O
</s>
<s>
Desktop-VMS	O
was	O
a	O
short	O
lived	O
distribution	O
of	O
VAX/VMS	O
sold	O
with	O
VAXstation	B-Device
systems	O
.	O
</s>
<s>
It	O
consisted	O
of	O
a	O
single	O
CD-ROM	B-Device
containing	O
a	O
bundle	O
of	O
VMS	O
,	O
DECwindows	B-Application
,	O
DECnet	B-Protocol
,	O
VAXcluster	O
support	O
,	O
and	O
a	O
setup	O
process	O
designed	O
for	O
non-technical	O
users	O
.	O
</s>
<s>
Desktop-VMS	O
had	O
its	O
own	O
versioning	O
scheme	O
beginning	O
with	O
V1.0	O
,	O
which	O
corresponded	O
to	O
the	O
V5.x	O
releases	O
of	O
VMS	O
.	O
</s>
<s>
An	O
unofficial	O
derivative	O
of	O
VAX/VMS	O
named	O
MOS	O
VP	O
(	O
)	O
was	O
created	O
in	O
the	O
Soviet	O
Union	O
during	O
the	O
1980s	O
for	O
the	O
SM	O
1700	O
line	O
of	O
VAX	B-Device
clone	O
hardware	O
.	O
</s>
<s>
With	O
the	O
V5.0	O
release	O
in	O
April	O
1988	O
,	O
DEC	O
began	O
to	O
refer	O
to	O
VAX/VMS	O
as	O
simply	O
VMS	O
in	O
its	O
documentation	O
.	O
</s>
<s>
In	O
July	O
1992	O
,	O
DEC	O
renamed	O
VAX/VMS	O
to	O
OpenVMS	O
as	O
an	O
indication	O
for	O
its	O
support	O
of	O
open	B-Operating_System
systems	I-Operating_System
industry	O
standards	O
such	O
as	O
POSIX	O
and	O
Unix	B-Application
compatibility	O
,	O
and	O
to	O
drop	O
the	O
VAX	B-Device
connection	O
since	O
a	O
migration	O
to	O
a	O
different	O
architecture	O
was	O
underway	O
.	O
</s>
<s>
DEC	O
began	O
using	O
the	O
OpenVMS	O
VAX	B-Device
name	O
with	O
the	O
V6.0	O
release	O
in	O
June	O
1993	O
.	O
</s>
<s>
During	O
the	O
1980s	O
,	O
DEC	O
planned	O
to	O
replace	O
the	O
VAX	B-Device
platform	O
and	O
the	O
VMS	O
operating	B-General_Concept
system	I-General_Concept
with	O
the	O
PRISM	B-Architecture
architecture	O
and	O
the	O
MICA	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
When	O
these	O
projects	O
were	O
cancelled	O
in	O
1988	O
,	O
a	O
team	O
was	O
set	O
up	O
to	O
design	O
new	O
VAX/VMS	O
systems	O
of	O
comparable	O
performance	O
to	O
RISC-based	B-Architecture
Unix	B-Application
systems	I-Application
.	O
</s>
<s>
After	O
a	O
number	O
of	O
failed	O
attempts	O
to	O
design	O
a	O
faster	O
VAX-compatible	O
processor	O
,	O
the	O
group	O
demonstrated	O
the	O
feasibility	O
of	O
porting	O
VMS	O
and	O
its	O
applications	O
to	O
a	O
RISC	B-Architecture
architecture	O
based	O
on	O
PRISM	B-Architecture
.	O
</s>
<s>
This	O
led	O
to	O
the	O
creation	O
of	O
the	O
Alpha	B-Device
architecture	O
.	O
</s>
<s>
The	O
project	O
to	O
port	O
VMS	O
to	O
Alpha	B-Device
began	O
in	O
1989	O
,	O
and	O
first	O
booted	O
on	O
a	O
prototype	O
Alpha	B-Device
EV3-based	O
Alpha	B-Device
Demonstration	O
Unit	O
in	O
early	O
1991	O
.	O
</s>
<s>
The	O
main	O
challenge	O
in	O
porting	O
VMS	O
to	O
a	O
new	O
architecture	O
was	O
that	O
VMS	O
and	O
the	O
VAX	B-Device
were	O
designed	O
together	O
,	O
meaning	O
that	O
VMS	O
was	O
dependent	O
on	O
certain	O
details	O
of	O
the	O
VAX	B-Device
architecture	O
.	O
</s>
<s>
Furthermore	O
,	O
a	O
significant	O
amount	O
of	O
the	O
VMS	O
kernel	B-Operating_System
,	O
layered	O
products	O
,	O
and	O
customer-developed	O
applications	O
were	O
implemented	O
in	O
VAX	B-Language
MACRO	I-Language
assembly	O
code	O
.	O
</s>
<s>
Some	O
of	O
the	O
changes	O
needed	O
to	O
decouple	O
VMS	O
from	O
the	O
VAX	B-Device
architecture	O
included	O
the	O
creation	O
of	O
the	O
MACRO-32	B-Language
compiler	O
,	O
which	O
treated	O
VAX	B-Language
MACRO	I-Language
as	O
a	O
high-level	B-Language
language	I-Language
,	O
and	O
compiled	O
it	O
to	O
Alpha	B-Device
object	B-Language
code	I-Language
,	O
and	O
the	O
emulation	B-Application
of	O
certain	O
low-level	O
details	O
of	O
the	O
VAX	B-Device
architecture	O
in	O
PALcode	B-General_Concept
,	O
such	O
as	O
interrupt	B-Application
handling	I-Application
and	O
atomic	O
queue	O
instructions	O
.	O
</s>
<s>
The	O
VMS	O
port	O
to	O
Alpha	B-Device
resulted	O
in	O
the	O
creation	O
of	O
two	O
separate	O
codebases	O
-	O
one	O
for	O
VAX	B-Device
,	O
and	O
for	O
Alpha	B-Device
.	O
</s>
<s>
The	O
Alpha	B-Device
code	O
library	O
was	O
based	O
on	O
a	O
snapshot	O
of	O
the	O
VAX/VMS	O
code	O
base	O
circa	O
V5.4-2	O
.	O
</s>
<s>
1992	O
saw	O
the	O
release	O
of	O
the	O
first	O
version	O
of	O
OpenVMS	O
for	O
Alpha	B-Device
AXP	I-Device
systems	O
,	O
designated	O
OpenVMS	O
AXP	O
V1.0	O
.	O
</s>
<s>
In	O
1994	O
,	O
with	O
the	O
release	O
of	O
OpenVMS	O
V6.1	O
,	O
feature	O
(	O
and	O
version	O
number	O
)	O
parity	O
between	O
the	O
VAX	B-Device
and	O
Alpha	B-Device
variants	O
was	O
achieved	O
,	O
this	O
was	O
the	O
so-called	O
Functional	O
Equivalence	O
release	O
.	O
</s>
<s>
The	O
decision	O
to	O
use	O
the	O
1.x	O
version	O
numbering	O
stream	O
for	O
the	O
pre-production	O
quality	O
releases	O
of	O
OpenVMS	O
AXP	O
caused	O
confusion	O
for	O
some	O
customers	O
,	O
and	O
was	O
not	O
repeated	O
in	O
the	O
subsequent	O
ports	O
of	O
OpenVMS	O
to	O
new	O
platforms	O
.	O
</s>
<s>
When	O
VMS	O
was	O
ported	O
to	O
Alpha	B-Device
,	O
it	O
was	O
initially	O
left	O
as	O
a	O
32-bit	O
only	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
This	O
was	O
done	O
to	O
ensure	O
backwards	B-General_Concept
compatibility	I-General_Concept
with	O
software	O
written	O
for	O
the	O
32-bit	O
VAX	B-Device
.	O
</s>
<s>
64-bit	O
addressing	O
was	O
first	O
added	O
for	O
Alpha	B-Device
in	O
the	O
V7.0	O
release	O
.	O
</s>
<s>
In	O
order	O
to	O
allow	O
64-bit	O
code	O
to	O
interoperate	O
with	O
older	O
32-bit	O
code	O
,	O
OpenVMS	O
does	O
not	O
create	O
a	O
distinction	O
between	O
32-bit	O
and	O
64-bit	O
executables	B-Application
,	O
but	O
instead	O
allows	O
for	O
both	O
32-bit	O
and	O
64-bit	O
pointers	O
to	O
be	O
used	O
within	O
the	O
same	O
code	O
.	O
</s>
<s>
The	O
64-bit	O
OpenVMS	O
Alpha	B-Device
releases	O
support	O
a	O
maximum	O
virtual	B-General_Concept
address	I-General_Concept
space	I-General_Concept
size	O
of	O
8TiB	O
(	O
a	O
43-bit	O
address	O
space	O
)	O
,	O
which	O
is	O
the	O
maximum	O
supported	O
by	O
the	O
Alpha	B-General_Concept
21064	I-General_Concept
and	O
Alpha	B-General_Concept
21164	I-General_Concept
.	O
</s>
<s>
One	O
of	O
the	O
more	O
noteworthy	O
Alpha-only	O
features	O
of	O
OpenVMS	O
was	O
OpenVMS	O
Galaxy	O
-	O
which	O
allowed	O
the	O
partitioning	B-Device
of	O
a	O
single	O
SMP	B-Operating_System
server	O
to	O
run	O
multiple	O
instances	O
of	O
OpenVMS	O
.	O
</s>
<s>
Galaxy	O
supported	O
dynamic	O
resource	O
allocation	O
to	O
running	O
partitions	B-Device
,	O
and	O
the	O
ability	O
to	O
share	O
memory	O
between	O
partitions	B-Device
.	O
</s>
<s>
In	O
2001	O
,	O
prior	O
to	O
its	O
acquisition	O
by	O
Hewlett-Packard	O
,	O
Compaq	O
announced	O
the	O
port	O
of	O
OpenVMS	O
to	O
the	O
Intel	B-General_Concept
Itanium	I-General_Concept
architecture	O
.	O
</s>
<s>
The	O
Itanium	B-General_Concept
port	O
was	O
the	O
result	O
of	O
Compaq	O
's	O
decision	O
to	O
discontinue	O
future	O
development	O
of	O
the	O
Alpha	B-Device
architecture	O
in	O
favour	O
of	O
adopting	O
the	O
then-new	O
Itanium	B-General_Concept
architecture	O
.	O
</s>
<s>
The	O
first	O
boot	O
consisted	O
of	O
booting	O
a	O
minimal	O
system	O
configuration	O
on	O
a	O
HP	O
i2000	O
workstation	B-Device
,	O
logging	O
in	O
as	O
the	O
SYSTEM	O
user	O
,	O
and	O
running	O
the	O
DIRECTORY	B-Application
command	O
.	O
</s>
<s>
The	O
Itanium	B-General_Concept
port	O
of	O
OpenVMS	O
supports	O
specific	O
models	O
and	O
configurations	O
of	O
HPE	B-General_Concept
Integrity	I-General_Concept
Servers	I-General_Concept
.	O
</s>
<s>
The	O
Itanium	B-General_Concept
releases	O
were	O
originally	O
named	O
HP	O
OpenVMS	O
Industry	O
Standard	O
64	O
for	O
Integrity	O
Servers	B-Application
,	O
although	O
the	O
names	O
OpenVMS	O
I64	O
or	O
OpenVMS	O
for	O
Integrity	O
Servers	B-Application
are	O
more	O
commonly	O
used	O
.	O
</s>
<s>
The	O
Itanium	B-General_Concept
port	O
was	O
accomplished	O
using	O
source	O
code	O
maintained	O
in	O
common	O
within	O
the	O
OpenVMS	O
Alpha	B-Device
source	O
code	O
library	O
,	O
with	O
the	O
addition	O
of	O
conditional	O
code	O
and	O
additional	O
modules	O
where	O
changes	O
specific	O
to	O
Itanium	B-General_Concept
were	O
required	O
.	O
</s>
<s>
This	O
required	O
certain	O
architectural	O
dependencies	O
of	O
OpenVMS	O
to	O
be	O
replaced	O
,	O
or	O
emulated	B-Application
in	O
software	O
.	O
</s>
<s>
Some	O
of	O
the	O
changes	O
included	O
using	O
the	O
Extensible	B-Architecture
Firmware	I-Architecture
Interface	I-Architecture
(	O
EFI	O
)	O
to	O
boot	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
reimplementing	O
the	O
functionality	O
previously	O
provided	O
by	O
Alpha	B-Device
PALcode	B-General_Concept
inside	O
the	O
kernel	B-Operating_System
,	O
using	O
new	O
executable	B-Application
file	I-Application
formats	I-Application
(	O
Executable	B-Application
and	O
Linkable	O
Format	O
and	O
DWARF	O
)	O
,	O
and	O
adopting	O
IEEE	O
754	O
as	O
the	O
default	O
floating	O
point	O
format	O
.	O
</s>
<s>
As	O
with	O
the	O
VAX	B-Device
to	O
Alpha	B-Device
port	O
,	O
a	O
binary	O
translator	O
for	O
Alpha	B-Device
to	O
Itanium	B-General_Concept
was	O
made	O
available	O
,	O
allowing	O
user	O
mode	O
OpenVMS	O
Alpha	B-Device
software	O
to	O
be	O
ported	O
to	O
Itanium	B-General_Concept
in	O
situations	O
where	O
it	O
was	O
not	O
possible	O
to	O
recompile	O
the	O
source	O
code	O
.	O
</s>
<s>
This	O
translator	O
is	O
known	O
as	O
the	O
Alpha	B-Device
Environment	O
Software	O
Translator	O
(	O
AEST	O
)	O
,	O
and	O
it	O
also	O
supported	O
translating	O
VAX	B-Device
executables	B-Application
which	O
had	O
already	O
translated	O
with	O
VEST	O
.	O
</s>
<s>
V8.2	O
was	O
also	O
released	O
for	O
Alpha	B-Device
,	O
subsequent	O
V8.x	O
releases	O
of	O
OpenVMS	O
have	O
maintained	O
feature	O
parity	O
between	O
the	O
Alpha	B-Device
and	O
Itanium	B-General_Concept
architectures	O
.	O
</s>
<s>
When	O
VMS	O
Software	O
Inc	O
.	O
(	O
VSI	O
)	O
announced	O
that	O
they	O
had	O
secured	O
the	O
rights	O
to	O
develop	O
the	O
OpenVMS	O
operating	B-General_Concept
system	I-General_Concept
from	O
HP	O
,	O
they	O
also	O
announced	O
their	O
intention	O
to	O
port	O
OpenVMS	O
to	O
the	O
x86-64	B-Device
architecture	O
.	O
</s>
<s>
The	O
porting	O
effort	O
ran	O
concurrently	O
with	O
the	O
establishment	O
of	O
the	O
company	O
,	O
as	O
well	O
as	O
the	O
development	O
of	O
VSI	O
's	O
own	O
Itanium	B-General_Concept
and	O
Alpha	B-Device
releases	O
of	O
OpenVMS	O
V8.4-x	O
.	O
</s>
<s>
The	O
x86-64	B-Device
port	O
is	O
targeted	O
for	O
specific	O
servers	B-Application
from	O
HPE	O
and	O
Dell	O
,	O
as	O
well	O
as	O
certain	O
virtual	O
machine	O
hypervisors	B-Operating_System
.	O
</s>
<s>
Initial	O
support	O
was	O
targeted	O
for	O
KVM	B-Application
and	O
VirtualBox	B-Operating_System
.	O
</s>
<s>
In	O
2021	O
,	O
the	O
x86-64	B-Device
port	O
was	O
demonstrated	O
running	O
on	O
an	O
Intel	O
Atom-based	O
single-board	B-Device
computer	I-Device
.	O
</s>
<s>
As	O
with	O
the	O
Alpha	B-Device
and	O
Itanium	B-General_Concept
ports	O
,	O
the	O
x86-64	B-Device
port	O
made	O
some	O
changes	O
to	O
simplify	O
porting	O
and	O
supporting	O
OpenVMS	O
on	O
the	O
new	O
platform	O
including	O
:	O
replacing	O
the	O
proprietary	B-Application
GEM	O
compiler	O
backend	O
used	O
by	O
the	O
VMS	O
compilers	O
with	O
LLVM	B-Application
,	O
changing	O
the	O
boot	O
process	O
so	O
that	O
OpenVMS	O
is	O
booted	O
from	O
a	O
memory	O
disk	O
,	O
and	O
simulating	O
the	O
four	O
privilege	B-Operating_System
levels	I-Operating_System
of	O
OpenVMS	O
in	O
software	O
since	O
only	O
two	O
of	O
x86-64	B-Device
'	O
s	O
privilege	B-Operating_System
levels	I-Operating_System
are	O
usable	O
by	O
OpenVMS	O
.	O
</s>
<s>
This	O
involved	O
booting	O
OpenVMS	O
on	O
VirtualBox	B-Operating_System
,	O
and	O
successfully	O
running	O
the	O
DIRECTORY	B-Application
command	O
.	O
</s>
<s>
This	O
consisted	O
of	O
the	O
OpenVMS	O
operating	B-General_Concept
system	I-General_Concept
running	O
in	O
a	O
VirtualBox	B-Operating_System
VM	O
with	O
certain	O
limitations	O
-	O
most	O
significantly	O
,	O
few	O
layered	O
products	O
were	O
available	O
,	O
and	O
code	O
can	O
only	O
be	O
compiled	O
for	O
x86-64	B-Device
using	O
cross	O
compilers	O
which	O
run	O
on	O
Itanium-based	O
OpenVMS	O
systems	O
.	O
</s>
<s>
Following	O
the	O
V9.0	O
release	O
,	O
VSI	O
released	O
a	O
series	O
of	O
updates	O
on	O
a	O
monthly	O
or	O
bimonthly	O
basis	O
which	O
added	O
additional	O
functionality	O
and	O
hypervisor	B-Operating_System
support	O
.	O
</s>
<s>
V9.1	O
shipped	O
as	O
an	O
ISO	B-General_Concept
image	I-General_Concept
which	O
can	O
be	O
installed	O
onto	O
a	O
variety	O
of	O
hypervisors	B-Operating_System
,	O
and	O
onto	O
HPE	B-Device
ProLiant	I-Device
DL380	I-Device
servers	B-Application
starting	O
with	O
the	O
V9.1-A	O
release	O
.	O
</s>
<s>
OpenVMS	O
9.2	O
for	O
x86-64	B-Device
reached	O
General	O
Availability	O
on	O
July	O
14	O
,	O
2022	O
.	O
</s>
<s>
During	O
the	O
1980s	O
,	O
the	O
MICA	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
for	O
the	O
PRISM	B-Architecture
architecture	O
was	O
intended	O
to	O
be	O
the	O
eventual	O
successor	O
to	O
VMS	O
.	O
</s>
<s>
MICA	B-Operating_System
was	O
designed	O
to	O
maintain	O
backwards	B-General_Concept
compatibility	I-General_Concept
with	O
VMS	O
applications	O
while	O
also	O
supporting	O
Ultrix	B-Operating_System
applications	O
on	O
top	O
of	O
the	O
same	O
kernel	B-Operating_System
.	O
</s>
<s>
MICA	B-Operating_System
was	O
ultimately	O
cancelled	O
along	O
with	O
the	O
rest	O
of	O
the	O
PRISM	B-Architecture
platform	O
,	O
leading	O
Dave	O
Cutler	O
to	O
leave	O
DEC	O
for	O
Microsoft	O
.	O
</s>
<s>
At	O
Microsoft	O
,	O
Cutler	O
led	O
the	O
creation	O
of	O
the	O
Windows	B-Device
NT	I-Device
operating	B-General_Concept
system	I-General_Concept
,	O
which	O
was	O
heavily	O
inspired	O
by	O
the	O
architecture	O
of	O
MICA	B-Operating_System
.	O
</s>
<s>
As	O
a	O
result	O
,	O
VMS	O
is	O
considered	O
an	O
ancestor	O
of	O
Windows	B-Device
NT	I-Device
,	O
together	O
with	O
RSX-11	B-Application
,	O
VAXELN	B-Operating_System
and	O
MICA	B-Operating_System
,	O
and	O
many	O
similarities	O
exist	O
between	O
VMS	O
and	O
NT	O
.	O
</s>
<s>
A	O
now-defunct	O
project	O
named	O
FreeVMS	O
attempted	O
to	O
develop	O
an	O
open	B-Application
source	I-Application
operating	B-General_Concept
system	I-General_Concept
following	O
VMS	O
conventions	O
.	O
</s>
<s>
FreeVMS	O
was	O
built	O
on	O
top	O
of	O
the	O
L4	B-Operating_System
microkernel	I-Operating_System
and	O
supported	O
the	O
x86-64	B-Device
architecture	O
.	O
</s>
<s>
Prior	O
work	O
investigating	O
the	O
implementation	O
of	O
VMS	O
using	O
a	O
microkernel-based	O
architecture	O
had	O
previously	O
been	O
undertaken	O
as	O
a	O
prototyping	O
exercise	O
by	O
DEC	O
employees	O
with	O
assistance	O
from	O
Carnegie	O
Mellon	O
University	O
using	O
the	O
Mach	B-Operating_System
3.0	I-Operating_System
microkernel	O
ported	O
to	O
VAXstation	B-Device
3100	O
hardware	O
,	O
adopting	O
a	O
multiserver	O
architectural	O
model	O
.	O
</s>
<s>
The	O
OpenVMS	O
operating	B-General_Concept
system	I-General_Concept
has	O
a	O
layered	O
architecture	O
,	O
consisting	O
of	O
a	O
privileged	O
Executive	O
,	O
an	O
intermediately-privileged	O
Command	B-Language
Language	I-Language
Interpreter	O
,	O
and	O
unprivileged	O
utilities	O
and	O
run-time	B-Library
libraries	I-Library
(	O
RTLs	O
)	O
.	O
</s>
<s>
Unprivileged	O
code	O
typically	O
invokes	O
the	O
functionality	O
of	O
the	O
Executive	O
through	O
system	O
services	O
(	O
equivalent	O
to	O
system	B-Operating_System
calls	I-Operating_System
in	O
other	O
operating	B-General_Concept
systems	I-General_Concept
)	O
.	O
</s>
<s>
OpenVMS	O
 '	O
layers	O
and	O
mechanisms	O
are	O
built	O
around	O
certain	O
features	O
of	O
the	O
VAX	B-Device
architecture	O
,	O
including	O
:	O
</s>
<s>
The	O
availability	O
of	O
four	O
processor	B-Operating_System
access	I-Operating_System
modes	I-Operating_System
(	O
named	O
Kernel	B-Operating_System
,	O
Executive	O
,	O
Supervisor	O
and	O
User	O
,	O
in	O
order	O
of	O
decreasing	O
privilege	O
)	O
.	O
</s>
<s>
Each	O
mode	O
has	O
its	O
own	O
stack	B-Application
,	O
and	O
each	O
memory	B-General_Concept
page	I-General_Concept
can	O
have	O
memory	B-General_Concept
protections	I-General_Concept
specified	O
per-mode	O
.	O
</s>
<s>
A	O
virtual	B-General_Concept
address	I-General_Concept
space	I-General_Concept
which	O
is	O
partitioned	O
between	O
process-private	O
space	O
sections	O
,	O
and	O
system	O
space	O
sections	O
which	O
are	O
common	O
to	O
all	O
processes	O
.	O
</s>
<s>
32	O
interrupt	B-Operating_System
priority	I-Operating_System
levels	I-Operating_System
which	O
are	O
used	O
for	O
synchronization	O
.	O
</s>
<s>
Hardware	O
support	O
for	O
delivering	O
asynchronous	B-Operating_System
system	I-Operating_System
traps	I-Operating_System
to	O
processes	O
.	O
</s>
<s>
These	O
VAX	B-Device
architecture	O
mechanisms	O
are	O
implemented	O
on	O
Alpha	B-Device
,	O
Itanium	B-General_Concept
and	O
x86-64	B-Device
by	O
either	O
mapping	O
to	O
corresponding	O
hardware	O
mechanisms	O
on	O
those	O
architectures	O
,	O
or	O
through	O
emulation	B-Application
(	O
via	O
PALcode	B-General_Concept
on	O
Alpha	B-Device
,	O
or	O
in	O
software	O
on	O
Itanium	B-General_Concept
and	O
x86-64	B-Device
)	O
.	O
</s>
<s>
The	O
Executive	O
is	O
further	O
subdivided	O
between	O
the	O
Kernel	B-Operating_System
,	O
which	O
consists	O
of	O
the	O
code	O
which	O
runs	O
at	O
the	O
kernel	B-Operating_System
access	O
mode	O
,	O
and	O
the	O
less-privileged	O
code	O
outside	O
of	O
the	O
Kernel	B-Operating_System
which	O
runs	O
at	O
the	O
executive	O
access	O
mode	O
.	O
</s>
<s>
The	O
components	O
of	O
the	O
Executive	O
which	O
run	O
at	O
executive	O
access	O
mode	O
include	O
the	O
Record	B-Application
Management	I-Application
Services	I-Application
,	O
and	O
certain	O
system	O
services	O
such	O
as	O
image	O
activation	O
.	O
</s>
<s>
The	O
main	O
distinction	O
between	O
the	O
kernel	B-Operating_System
and	O
executive	O
access	O
modes	O
is	O
that	O
most	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
's	O
core	O
data	O
structures	O
can	O
be	O
read	O
from	O
executive	O
mode	O
,	O
but	O
require	O
kernel	B-Operating_System
mode	O
to	O
be	O
written	O
to	O
.	O
</s>
<s>
Code	O
running	O
at	O
executive	O
mode	O
can	O
switch	O
to	O
kernel	B-Operating_System
mode	O
at	O
will	O
,	O
meaning	O
that	O
the	O
barrier	O
between	O
the	O
kernel	B-Operating_System
and	O
executive	O
modes	O
is	O
intended	O
as	O
a	O
safeguard	O
against	O
accidental	O
corruption	O
as	O
opposed	O
to	O
a	O
security	O
mechanism	O
.	O
</s>
<s>
The	O
Kernel	B-Operating_System
comprises	O
the	O
operating	B-General_Concept
system	I-General_Concept
's	O
core	O
data	O
structures	O
(	O
e.g.	O
</s>
<s>
The	O
Kernel	B-Operating_System
is	O
typically	O
described	O
as	O
having	O
three	O
major	O
subsystems	O
:	O
I/O	O
,	O
Process	O
and	O
Time	O
Management	O
,	O
Memory	O
Management	O
.	O
</s>
<s>
In	O
addition	O
,	O
other	O
functionality	O
such	O
as	O
logical	O
name	O
management	O
,	O
synchronization	O
and	O
system	O
service	O
dispatch	O
are	O
implemented	O
inside	O
the	O
Kernel	B-Operating_System
.	O
</s>
<s>
OpenVMS	O
allows	O
user	O
mode	O
code	O
with	O
suitable	O
privileges	O
to	O
switch	O
to	O
executive	O
or	O
kernel	B-Operating_System
mode	O
using	O
the	O
$CMEXEC	O
and	O
$CMKRNL	O
system	O
services	O
,	O
respectively	O
.	O
</s>
<s>
In	O
addition	O
to	O
allowing	O
third-party	O
extensions	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
Privileged	O
Images	O
are	O
used	O
by	O
core	O
operating	B-General_Concept
system	I-General_Concept
utilities	O
to	O
manipulate	O
operating	B-General_Concept
system	I-General_Concept
data	O
structures	O
through	O
undocumented	O
interfaces	O
.	O
</s>
<s>
The	O
typical	O
user	O
and	O
application	O
interface	O
into	O
the	O
file	B-Application
system	I-Application
is	O
the	O
Record	B-Application
Management	I-Application
Services	I-Application
(	O
RMS	B-Application
)	O
,	O
although	O
applications	O
can	O
interface	O
directly	O
with	O
the	O
underlying	O
file	B-Application
system	I-Application
through	O
the	O
QIO	B-Operating_System
system	O
services	O
.	O
</s>
<s>
The	O
file	B-Application
systems	I-Application
supported	O
by	O
VMS	O
are	O
referred	O
to	O
as	O
the	O
Files-11	B-Application
On-Disk	O
Structures	O
(	O
ODS	O
)	O
,	O
the	O
most	O
significant	O
of	O
which	O
are	O
ODS-2	O
and	O
ODS-5	B-Application
.	O
</s>
<s>
VMS	O
is	O
also	O
capable	O
of	O
accessing	O
files	O
on	O
ISO	B-Application
9660	I-Application
CD-ROMs	B-Device
and	O
magnetic	O
tape	O
with	O
ANSI	O
tape	O
labels	O
.	O
</s>
<s>
Files-11	B-Application
is	O
limited	O
to	O
2TiB	O
volumes	O
.	O
</s>
<s>
DEC	O
attempted	O
to	O
replace	O
it	O
with	O
a	O
log-structured	B-Application
file	I-Application
system	I-Application
file	B-Application
system	I-Application
named	O
Spiralog	O
first	O
released	O
in	O
1995	O
.	O
</s>
<s>
Instead	O
,	O
there	O
has	O
been	O
discussion	O
of	O
porting	O
the	O
open	B-Application
source	I-Application
GFS2	O
file	B-Application
system	I-Application
to	O
OpenVMS	O
.	O
</s>
<s>
An	O
OpenVMS	O
Command	B-Language
Language	I-Language
Interpreter	O
(	O
CLI	B-Application
)	O
implements	O
a	O
command-line	B-Application
interface	I-Application
for	O
OpenVMS	O
;	O
responsible	O
for	O
executing	O
individual	O
commands	O
,	O
as	O
well	O
as	O
command	O
procedures	O
(	O
equivalent	O
to	O
shell	B-Language
scripts	I-Language
or	O
batch	O
files	O
)	O
.	O
</s>
<s>
The	O
standard	O
CLI	B-Application
for	O
OpenVMS	O
is	O
the	O
DIGITAL	B-Operating_System
Command	I-Operating_System
Language	I-Operating_System
,	O
although	O
other	O
options	O
are	O
available	O
as	O
well	O
.	O
</s>
<s>
Unlike	O
Unix	B-Application
shells	I-Application
,	O
which	O
typically	O
run	O
in	O
their	O
own	O
isolated	O
process	O
and	O
behave	O
like	O
any	O
other	O
user	O
mode	O
program	O
,	O
OpenVMS	O
CLIs	O
are	O
an	O
optional	O
component	O
of	O
a	O
process	O
,	O
which	O
exist	O
alongside	O
any	O
executable	B-Application
image	O
which	O
that	O
process	O
may	O
run	O
.	O
</s>
<s>
Whereas	O
a	O
Unix	B-Application
shell	I-Application
will	O
typically	O
run	O
executables	B-Application
by	O
creating	O
a	O
separate	O
process	O
using	O
fork-exec	B-Operating_System
,	O
an	O
OpenVMS	O
CLI	B-Application
will	O
typically	O
load	O
the	O
executable	B-Application
image	O
into	O
the	O
same	O
process	O
,	O
transfer	O
control	O
to	O
the	O
image	O
,	O
and	O
ensure	O
that	O
control	O
is	O
transferred	O
back	O
to	O
CLI	B-Application
once	O
the	O
image	O
has	O
exited	O
and	O
that	O
the	O
process	O
is	O
returned	O
to	O
its	O
original	O
state	O
.	O
</s>
<s>
Due	O
to	O
the	O
fact	O
that	O
the	O
CLI	B-Application
is	O
loaded	O
into	O
the	O
same	O
address	O
space	O
as	O
user	O
code	O
,	O
and	O
that	O
the	O
CLI	B-Application
is	O
responsible	O
for	O
invoking	O
image	O
activation	O
and	O
image	O
rundown	O
,	O
the	O
CLI	B-Application
is	O
mapped	O
into	O
the	O
process	O
address	O
space	O
at	O
supervisor	O
access	O
mode	O
-	O
a	O
higher	O
level	O
of	O
privilege	O
than	O
most	O
user	O
code	O
.	O
</s>
<s>
This	O
is	O
in	O
order	O
to	O
prevent	O
accidental	O
or	O
malicious	O
manipulation	O
of	O
the	O
CLI	B-Application
's	O
code	O
and	O
data	O
structures	O
by	O
user	O
mode	O
code	O
.	O
</s>
<s>
OpenVMS	O
supports	O
clustering	B-Architecture
(	O
first	O
called	O
VAXcluster	O
and	O
later	O
VMScluster	O
)	O
,	O
where	O
multiple	O
computers	O
run	O
their	O
own	O
instance	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Communication	O
across	O
nodes	O
provides	O
a	O
single	B-Operating_System
system	I-Operating_System
image	I-Operating_System
abstraction	O
.	O
</s>
<s>
Nodes	O
may	O
be	O
connected	O
to	O
each	O
other	O
via	O
a	O
proprietary	B-Application
hardware	O
connection	O
called	O
Cluster	O
Interconnect	O
or	O
via	O
a	O
standard	O
Ethernet	O
LAN	B-General_Concept
.	O
</s>
<s>
(	O
VAX	B-Device
,	O
Alpha	B-Device
,	O
and	O
Itanium	B-General_Concept
computers	O
each	O
have	O
a	O
different	O
architecture	O
.	O
)	O
</s>
<s>
The	O
DECnet	B-Protocol
protocol	O
suite	O
is	O
tightly	O
integrated	O
into	O
VMS	O
,	O
allowing	O
remote	O
logins	O
,	O
as	O
well	O
as	O
transparent	O
access	O
to	O
files	O
,	O
printers	O
and	O
other	O
resources	O
on	O
VMS	O
systems	O
over	O
a	O
network	O
.	O
</s>
<s>
Modern	O
versions	O
of	O
VMS	O
support	O
both	O
the	O
traditional	O
Phase	O
IV	O
DECnet	B-Protocol
protocol	O
,	O
as	O
well	O
as	O
the	O
OSI-compatible	B-Protocol
Phase	O
V	O
(	O
also	O
known	O
as	O
DECnet-Plus	O
)	O
.	O
</s>
<s>
Support	O
for	O
TCP/IP	B-Protocol
is	O
provided	O
by	O
the	O
optional	O
TCP/IP	B-Protocol
Services	O
for	O
OpenVMS	O
layered	O
product	O
(	O
originally	O
known	O
as	O
the	O
VMS/ULTRIX	O
Connection	O
,	O
then	O
as	O
the	O
ULTRIX	B-Operating_System
Communications	O
Extensions	O
or	O
UCX	O
)	O
.	O
</s>
<s>
TCP/IP	B-Protocol
Services	O
is	O
based	O
on	O
a	O
port	O
of	O
the	O
BSD	B-Operating_System
network	O
stack	B-Application
to	O
OpenVMS	O
,	O
along	O
with	O
support	O
for	O
common	O
protocols	O
such	O
as	O
SSH	B-Protocol
,	O
DHCP	B-Protocol
,	O
FTP	B-Protocol
and	O
SMTP	B-Protocol
.	O
</s>
<s>
DEC	O
sold	O
a	O
software	O
package	O
named	O
PATHWORKS	B-Application
(	O
originally	O
known	O
as	O
the	O
Personal	B-Device
Computer	I-Device
Systems	O
Architecture	O
or	O
PCSA	O
)	O
which	O
allowed	O
personal	B-Device
computers	I-Device
running	O
MS-DOS	B-Application
,	O
Microsoft	B-Application
Windows	I-Application
or	O
OS/2	B-Application
,	O
or	O
the	O
Apple	B-Device
Macintosh	I-Device
to	O
serve	O
as	O
a	O
terminal	O
for	O
VMS	O
systems	O
,	O
or	O
to	O
use	O
VMS	O
systems	O
as	O
a	O
file	O
or	O
print	O
server	O
.	O
</s>
<s>
PATHWORKS	B-Application
was	O
later	O
renamed	O
to	O
Advanced	B-Application
Server	I-Application
for	I-Application
OpenVMS	I-Application
,	O
and	O
was	O
eventually	O
replaced	O
with	O
a	O
VMS	O
port	O
of	O
Samba	B-Language
at	O
the	O
time	O
of	O
the	O
Itanium	B-General_Concept
port	O
.	O
</s>
<s>
DEC	O
provided	O
the	O
Local	B-General_Concept
Area	I-General_Concept
Transport	I-General_Concept
(	O
LAT	O
)	O
protocol	O
which	O
allowed	O
remote	O
terminals	O
and	O
printers	O
to	O
be	O
attached	O
to	O
a	O
VMS	O
system	O
through	O
a	O
terminal	B-Device
server	I-Device
such	O
as	O
one	O
of	O
the	O
DECserver	B-Device
family	O
.	O
</s>
<s>
Among	O
OpenVMS	O
's	O
notable	O
features	O
is	O
the	O
Common	O
Language	O
Environment	O
,	O
a	O
strictly	O
defined	O
standard	O
that	O
specifies	O
calling	O
conventions	O
for	O
functions	O
and	O
routines	O
,	O
including	O
use	O
of	O
stacks	B-Application
,	O
registers	B-General_Concept
,	O
etc.	O
,	O
independent	O
of	O
programming	O
language	O
.	O
</s>
<s>
Because	O
of	O
this	O
,	O
it	O
is	O
possible	O
to	O
call	O
a	O
routine	O
written	O
in	O
one	O
language	O
(	O
for	O
example	O
,	O
Fortran	B-Application
)	O
from	O
another	O
(	O
for	O
example	O
,	O
COBOL	B-Application
)	O
,	O
without	O
needing	O
to	O
know	O
the	O
implementation	O
details	O
of	O
the	O
target	O
language	O
.	O
</s>
<s>
In	O
addition	O
,	O
a	O
number	O
of	O
text	B-Application
editors	I-Application
are	O
included	O
in	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
including	O
EDT	B-Application
,	O
EVE	B-Application
and	O
TECO	B-Application
.	O
</s>
<s>
It	O
allows	O
breakpoints	O
,	O
watchpoints	O
and	O
interactive	O
runtime	O
program	O
debugging	O
either	O
using	O
a	O
command	B-Application
line	I-Application
or	O
graphical	B-Application
user	I-Application
interface	I-Application
.	O
</s>
<s>
In	O
2019	O
,	O
VSI	O
released	O
an	O
officially-supported	O
Integrated	B-Application
Development	I-Application
Environment	I-Application
for	O
VMS	O
based	O
on	O
Visual	B-Language
Studio	I-Language
Code	I-Language
.	O
</s>
<s>
This	O
allows	O
VMS	O
applications	O
to	O
be	O
developed	O
and	O
debugged	O
remotely	O
from	O
a	O
Microsoft	B-Application
Windows	I-Application
,	O
macOS	B-Application
or	O
Linux	B-Application
workstation	B-Device
.	O
</s>
<s>
DEC	O
created	O
a	O
number	O
of	O
optional	O
database	O
products	O
for	O
VMS	O
,	O
some	O
of	O
which	O
were	O
marketed	O
as	O
the	O
VAX	B-Device
Information	O
Architecture	O
family	O
.	O
</s>
<s>
Rdb	B-Application
–	O
A	O
relational	B-Application
database	I-Application
system	O
which	O
originally	O
used	O
the	O
proprietary	B-Application
Relational	O
Data	O
Operator	O
(	O
RDO	O
)	O
query	O
interface	O
,	O
but	O
later	O
gained	O
SQL	B-Language
support	O
.	O
</s>
<s>
DBMS	O
–	O
A	O
database	O
management	O
system	O
which	O
uses	O
the	O
CODASYL	B-Language
network	B-General_Concept
model	I-General_Concept
and	O
Data	O
Manipulation	O
Language	O
(	O
DML	O
)	O
.	O
</s>
<s>
Digital	B-Language
Standard	I-Language
MUMPS	I-Language
(	O
DSM	O
)	O
–	O
an	O
integrated	O
programming	O
language	O
and	O
key-value	B-Data_Structure
database	I-Data_Structure
.	O
</s>
<s>
Common	O
Data	O
Dictionary	O
(	O
CDD	O
)	O
–	O
a	O
central	O
database	B-Application
schema	I-Application
repository	O
,	O
which	O
allowed	O
schemas	B-Application
to	O
be	O
shared	O
between	O
different	O
applications	O
,	O
and	O
data	O
definitions	O
to	O
be	O
generated	O
for	O
different	O
programming	O
languages	O
.	O
</s>
<s>
DATATRIEVE	B-Application
–	O
a	O
query	O
and	O
reporting	O
tool	O
which	O
could	O
access	O
data	O
from	O
RMS	B-Application
files	O
as	O
well	O
as	O
Rdb	B-Application
and	O
DBMS	O
databases	O
.	O
</s>
<s>
Application	O
Control	O
Management	O
System	O
(	O
ACMS	O
)	O
–	O
A	O
transaction	B-General_Concept
processing	I-General_Concept
monitor	I-General_Concept
,	O
which	O
allows	O
applications	O
to	O
be	O
created	O
using	O
a	O
high-level	O
Task	O
Description	O
Language	O
(	O
TDL	O
)	O
.	O
</s>
<s>
Individual	O
steps	O
of	O
a	O
transaction	O
can	O
be	O
implemented	O
using	O
DCL	B-Operating_System
commands	O
,	O
or	O
Common	O
Language	O
Environment	O
procedures	O
.	O
</s>
<s>
User	O
interfaces	O
can	O
be	O
implemented	O
using	O
TDMS	O
,	O
DECforms	O
or	O
Digital	O
's	O
ALL-IN-1	B-Application
office	O
automation	O
product	O
.	O
</s>
<s>
RALLY	O
,	O
DECadmire	O
–	O
Fourth-generation	B-Language
programming	I-Language
languages	I-Language
(	O
4GLs	B-Language
)	O
for	O
generating	O
database-backed	O
applications	O
.	O
</s>
<s>
DECadmire	O
featured	O
integration	O
with	O
ACMS	O
,	O
and	O
later	O
provided	O
support	O
for	O
generating	O
Visual	B-Language
Basic	I-Language
client-server	B-Operating_System
applications	O
for	O
Windows	B-Application
PCs	I-Application
.	O
</s>
<s>
In	O
1994	O
,	O
DEC	O
sold	O
Rdb	B-Application
,	O
DBMS	O
and	O
CDD	O
to	O
Oracle	B-Application
,	O
where	O
they	O
remain	O
under	O
active	O
development	O
.	O
</s>
<s>
In	O
1995	O
,	O
DEC	O
sold	O
DSM	O
to	O
InterSystems	B-Application
,	O
who	O
renamed	O
it	O
Open	O
M	B-Language
,	O
and	O
eventually	O
replaced	O
it	O
with	O
their	O
Caché	B-Language
product	O
.	O
</s>
<s>
Examples	O
of	O
third-party	O
database	O
management	O
systems	O
for	O
OpenVMS	O
include	O
MariaDB	B-Application
,	O
Mimer	B-Application
SQL	I-Application
(	O
Itanium	B-General_Concept
and	O
x86-64	B-Device
)	O
,	O
and	O
System	O
1032	O
.	O
</s>
<s>
VMS	O
was	O
originally	O
designed	O
to	O
be	O
used	O
and	O
managed	O
interactively	O
using	O
DEC	O
's	O
text-based	B-Application
video	B-General_Concept
terminals	I-General_Concept
such	O
as	O
the	O
VT100	B-Device
,	O
or	O
hardcopy	O
terminals	O
such	O
as	O
the	O
DECwriter	B-Application
series	O
.	O
</s>
<s>
Since	O
the	O
introduction	O
of	O
the	O
VAXstation	B-Device
line	O
in	O
1984	O
,	O
VMS	O
has	O
optionally	O
supported	O
graphical	B-Application
user	I-Application
interfaces	I-Application
for	O
use	O
with	O
workstations	B-Device
or	O
X	B-Protocol
terminals	I-Protocol
such	O
as	O
the	O
VT1000	B-Device
series	O
.	O
</s>
<s>
The	O
DIGITAL	B-Operating_System
Command	I-Operating_System
Language	I-Operating_System
(	O
DCL	B-Operating_System
)	O
,	O
has	O
served	O
as	O
the	O
primary	O
command	B-Language
language	I-Language
interpreter	O
(	O
CLI	B-Application
)	O
of	O
OpenVMS	O
since	O
the	O
first	O
release	O
.	O
</s>
<s>
Other	O
official	O
CLIs	O
available	O
for	O
VMS	O
include	O
the	O
RSX-11	B-Application
MCR	O
(	O
VAX	B-Device
only	O
)	O
,	O
and	O
various	O
Unix	B-Application
shells	I-Application
.	O
</s>
<s>
DEC	O
provided	O
tools	O
for	O
creating	O
text-based	B-Application
user	I-Application
interface	I-Application
applications	O
–	O
the	O
Form	O
Management	O
System	O
(	O
FMS	O
)	O
and	O
Terminal	O
Data	O
Management	O
System	O
(	O
TDMS	O
)	O
,	O
later	O
succeeded	O
by	O
DECforms	O
.	O
</s>
<s>
A	O
lower	O
level	O
interface	O
named	O
Screen	O
Management	O
Services	O
(	O
SMG$	O
)	O
,	O
comparable	O
to	O
Unix	B-Device
curses	I-Device
,	O
also	O
exists	O
.	O
</s>
<s>
Over	O
the	O
years	O
,	O
VMS	O
has	O
gone	O
through	O
a	O
number	O
of	O
different	O
GUI	B-Application
toolkits	O
and	O
interfaces	O
:	O
</s>
<s>
The	O
original	O
graphical	B-Application
user	I-Application
interface	I-Application
for	O
VMS	O
was	O
a	O
proprietary	B-Application
windowing	B-Application
system	I-Application
known	O
as	O
the	O
VMS	O
Workstation	B-Device
Software	O
(	O
VWS	O
)	O
,	O
which	O
was	O
first	O
released	O
for	O
the	O
VAXstation	B-Device
I	O
in	O
1984	O
.	O
</s>
<s>
It	O
ran	O
on	O
a	O
limited	O
selection	O
of	O
VAX	B-Device
hardware	O
.	O
</s>
<s>
In	O
1989	O
,	O
DEC	O
replaced	O
VWS	O
with	O
a	O
new	O
X11-based	O
windowing	B-Application
system	I-Application
named	O
DECwindows	B-Application
.	O
</s>
<s>
It	O
was	O
first	O
included	O
in	O
VAX/VMS	O
V5.1	O
.	O
</s>
<s>
Early	O
versions	O
of	O
DECwindows	B-Application
featured	O
an	O
interface	O
built	O
on	O
top	O
of	O
a	O
proprietary	B-Application
toolkit	O
named	O
the	O
X	B-Operating_System
User	O
Interface	O
(	O
XUI	O
)	O
.	O
</s>
<s>
A	O
layered	O
product	O
named	O
UISX	O
was	O
provided	O
to	O
allow	O
VWS/UIS	O
applications	O
to	O
run	O
on	O
top	O
of	O
DECwindows	B-Application
.	O
</s>
<s>
Parts	O
of	O
XUI	O
were	O
subsequently	O
used	O
by	O
the	O
Open	B-Application
Software	I-Application
Foundation	I-Application
as	O
the	O
foundation	O
of	O
the	O
Motif	B-Application
toolkit	I-Application
.	O
</s>
<s>
In	O
1991	O
,	O
DEC	O
replaced	O
XUI	O
with	O
the	O
Motif	B-Application
toolkit	I-Application
,	O
creating	O
DECwindows	B-Application
Motif	B-Device
.	O
</s>
<s>
As	O
a	O
result	O
,	O
the	O
Motif	B-Device
Window	I-Device
Manager	I-Device
became	O
the	O
default	O
DECwindows	B-Application
interface	O
in	O
OpenVMS	O
V6.0	O
,	O
although	O
the	O
XUI	O
window	O
manager	O
remained	O
as	O
an	O
option	O
.	O
</s>
<s>
In	O
1996	O
,	O
as	O
part	O
of	O
OpenVMS	O
V7.1	O
,	O
DEC	O
released	O
the	O
New	O
Desktop	O
interface	O
for	O
DECwindows	B-Application
Motif	B-Device
,	O
based	O
on	O
the	O
Common	B-Application
Desktop	I-Application
Environment	I-Application
(	O
CDE	B-Application
)	O
.	O
</s>
<s>
On	O
Alpha	B-Device
and	O
Itanium	B-General_Concept
systems	O
,	O
it	O
is	O
still	O
possible	O
to	O
select	O
the	O
older	O
MWM-based	O
UI	O
(	O
referred	O
to	O
as	O
the	O
"	O
DECwindows	B-Application
Desktop	O
"	O
)	O
at	O
login	O
time	O
.	O
</s>
<s>
The	O
New	O
Desktop	O
was	O
never	O
ported	O
to	O
the	O
VAX	B-Device
releases	O
of	O
OpenVMS	O
.	O
</s>
<s>
Versions	O
of	O
VMS	O
running	O
on	O
DEC	B-Device
Alpha	I-Device
workstations	B-Device
in	O
the	O
1990s	O
supported	O
OpenGL	B-Application
and	O
Accelerated	B-Architecture
Graphics	I-Architecture
Port	I-Architecture
(	O
AGP	O
)	O
graphics	O
adapters	O
.	O
</s>
<s>
VMS	O
also	O
provides	O
support	O
for	O
older	O
graphics	O
standards	O
such	O
as	O
GKS	O
and	O
PHIGS	B-Library
.	O
</s>
<s>
Modern	O
versions	O
of	O
DECwindows	B-Application
are	O
based	O
on	O
X.Org	B-Operating_System
Server	I-Operating_System
.	O
</s>
<s>
Early	O
versions	O
of	O
VMS	O
included	O
a	O
number	O
of	O
privileged	O
user	O
accounts	O
(	O
including	O
SYSTEM	O
,	O
FIELD	O
,	O
SYSTEST	O
and	O
DECNET	B-Protocol
)	O
with	O
default	O
passwords	O
which	O
were	O
often	O
left	O
unchanged	O
by	O
system	O
managers	O
.	O
</s>
<s>
A	O
number	O
of	O
computer	O
worms	O
for	O
VMS	O
including	O
the	O
WANK	O
worm	O
and	O
the	O
Father	O
Christmas	O
worm	O
exploited	O
these	O
default	O
passwords	O
to	O
gain	O
access	O
to	O
nodes	O
on	O
DECnet	B-Protocol
networks	O
.	O
</s>
<s>
This	O
issue	O
was	O
also	O
described	O
by	O
Clifford	O
Stoll	O
in	O
The	O
Cuckoo	O
's	O
Egg	O
as	O
a	O
means	O
by	O
which	O
Markus	O
Hess	O
gained	O
unauthorized	O
access	O
to	O
VAX/VMS	O
systems	O
.	O
</s>
<s>
A	O
33-year-old	O
vulnerability	O
in	O
VMS	O
on	O
VAX	B-Device
and	O
Alpha	B-Device
was	O
discovered	O
in	O
2017	O
and	O
assigned	O
the	O
CVE	O
ID	O
.	O
</s>
<s>
On	O
the	O
affected	O
platforms	O
,	O
this	O
vulnerability	O
allowed	O
an	O
attacker	O
with	O
access	O
to	O
the	O
DCL	B-Operating_System
command	B-Application
line	I-Application
to	O
carry	O
out	O
a	O
privilege	O
escalation	O
attack	O
.	O
</s>
<s>
The	O
vulnerability	O
relies	O
on	O
exploiting	O
a	O
buffer	B-General_Concept
overflow	I-General_Concept
bug	O
in	O
the	O
DCL	B-Operating_System
command	O
processing	O
code	O
,	O
the	O
ability	O
for	O
a	O
user	O
to	O
interrupt	B-Application
a	O
running	O
image	O
(	O
program	O
executable	B-Application
)	O
with	O
and	O
return	O
to	O
the	O
DCL	B-Operating_System
prompt	O
,	O
and	O
the	O
fact	O
that	O
DCL	B-Operating_System
retains	O
the	O
privileges	O
of	O
the	O
interrupted	O
image	O
.	O
</s>
<s>
The	O
buffer	B-General_Concept
overflow	I-General_Concept
bug	O
allowed	O
shellcode	O
to	O
be	O
executed	O
with	O
the	O
privileges	O
of	O
an	O
interrupted	O
image	O
.	O
</s>
<s>
Various	O
official	O
Unix	B-Application
and	O
POSIX	O
compatibility	O
layers	O
were	O
created	O
for	O
VMS	O
.	O
</s>
<s>
The	O
first	O
of	O
which	O
was	O
DEC/Shell	O
-	O
which	O
was	O
a	O
layered	O
product	O
consisting	O
of	O
ports	O
of	O
the	O
Version	B-Operating_System
7	I-Operating_System
Unix	I-Operating_System
Bourne	B-Device
shell	I-Device
and	O
several	O
other	O
Unix	B-Application
utilities	O
to	O
VAX/VMS	O
.	O
</s>
<s>
In	O
1992	O
,	O
DEC	O
released	O
the	O
POSIX	O
for	O
OpenVMS	O
layered	O
product	O
,	O
which	O
included	O
a	O
shell	O
based	O
on	O
the	O
KornShell	B-Language
.	O
</s>
<s>
POSIX	O
for	O
OpenVMS	O
was	O
later	O
replaced	O
by	O
the	O
open	B-Application
source	I-Application
GNV	O
(	O
GNU	B-Operating_System
's	O
not	O
VMS	O
)	O
project	O
,	O
which	O
was	O
first	O
included	O
in	O
OpenVMS	O
media	O
in	O
2002	O
.	O
</s>
<s>
Amongst	O
other	O
GNU	B-Operating_System
tools	O
,	O
GNV	O
includes	O
a	O
port	O
of	O
the	O
Bash	B-Operating_System
shell	I-Operating_System
to	O
VMS	O
.	O
</s>
<s>
Examples	O
of	O
third	O
party	O
Unix	B-Application
compatibility	O
layers	O
for	O
VMS	O
include	O
Eunice	B-Operating_System
.	O
</s>
<s>
Prior	O
to	O
the	O
x86-64	B-Device
port	O
,	O
the	O
age	O
and	O
cost	O
of	O
hardware	O
capable	O
of	O
running	O
OpenVMS	O
made	O
emulators	B-Application
such	O
as	O
SIMH	B-Application
a	O
common	O
choice	O
for	O
hobbyist	O
installations	O
.	O
</s>
<s>
The	O
CLP	O
was	O
launched	O
in	O
July	O
2020	O
,	O
and	O
provides	O
licenses	O
for	O
VSI	O
OpenVMS	O
releases	O
on	O
Alpha	B-Device
,	O
Integrity	O
and	O
x86-64	B-Device
systems	O
.	O
</s>
<s>
OpenVMS	O
for	O
VAX	B-Device
is	O
not	O
covered	O
by	O
the	O
CLP	O
,	O
since	O
there	O
are	O
no	O
VSI	O
releases	O
of	O
OpenVMS	O
VAX	B-Device
,	O
and	O
the	O
old	O
versions	O
are	O
still	O
owned	O
by	O
HPE	O
.	O
</s>
