<s>
VM	O
(	O
often	O
:	O
VM/CMS	O
)	O
is	O
a	O
family	O
of	O
IBM	O
virtual	B-Architecture
machine	I-Architecture
operating	B-General_Concept
systems	I-General_Concept
used	O
on	O
IBM	B-Device
mainframes	I-Device
System/370	B-Device
,	O
System/390	B-Device
,	O
zSeries	O
,	O
System	B-Device
z	I-Device
and	O
compatible	O
systems	O
,	O
including	O
the	O
Hercules	B-Application
emulator	I-Application
for	O
personal	O
computers	O
.	O
</s>
<s>
VM/370	O
,	O
released	O
in	O
1972	O
,	O
is	O
a	O
System/370	B-Device
reimplementation	O
of	O
earlier	O
CP/CMS	B-Application
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Release	O
1	O
added	O
EXEC2	B-Application
and	O
XEDIT	B-Application
System	O
Product	O
Editor	O
;	O
Release	O
3	O
added	O
REXX	B-Language
;	O
Release	O
6	O
added	O
the	O
shared	O
filesystem	O
.	O
</s>
<s>
VM/SP	O
HPO	O
adds	O
additional	O
device	O
support	O
and	O
functionality	O
to	O
VM/SP	O
,	O
and	O
allows	O
certain	O
S/370	B-Device
machines	O
that	O
can	O
utilize	O
more	O
than	O
16	O
MB	O
of	O
real	O
storage	O
to	O
do	O
so	O
,	O
up	O
to	O
64	O
MB	O
.	O
</s>
<s>
This	O
version	O
was	O
intended	O
for	O
users	O
that	O
would	O
be	O
running	O
multiple	O
S/370	B-Device
guests	O
at	O
once	O
.	O
</s>
<s>
VM/XA	B-Application
MA	O
is	O
intended	O
to	O
ease	O
the	O
migration	O
from	O
MVS/370	O
to	O
MVS/XA	O
by	O
allowing	O
both	O
to	O
run	O
concurrently	O
on	O
the	O
same	O
processor	O
complex	O
.	O
</s>
<s>
VM/XA	B-Application
SF	O
is	O
an	O
upgraded	O
VM/XA	B-Application
MA	O
with	O
improved	O
functionality	O
and	O
performance	O
.	O
</s>
<s>
VM/XA	B-Application
SF	O
is	O
an	O
upgraded	O
VM/XA	B-Application
MA	O
with	O
improved	O
functionality	O
and	O
performance	O
,	O
offered	O
as	O
a	O
replacement	O
for	O
VM/SP	O
HPO	O
on	O
machines	O
supporting	O
S/370	B-Device
-XA	I-Device
.	O
</s>
<s>
It	O
includes	O
a	O
version	O
of	O
CMS	O
that	O
can	O
run	O
in	O
either	O
S/370	B-Device
or	O
S/370	B-Device
-XA	I-Device
mode	O
.	O
</s>
<s>
VM/ESA	O
provides	O
the	O
facilities	O
of	O
VM/SP	O
,	O
VM/SP	O
HPO	O
and	O
VM/XA	B-Application
SP	O
.	O
</s>
<s>
VM/ESA	O
version	O
1	O
can	O
run	O
in	O
S/370	B-Device
,	O
ESA/370	O
or	O
ESA/390	O
mode	O
;	O
it	O
does	O
not	O
support	O
S/370	B-Device
XA	O
mode	O
.	O
</s>
<s>
The	O
S/370	B-Device
-capable	O
versions	O
of	O
VM/ESA	O
were	O
actually	O
their	O
own	O
separate	O
version	O
from	O
the	O
ESA/390	O
versions	O
of	O
VM/ESA	O
,	O
as	O
the	O
S/370	B-Device
versions	O
are	O
based	O
on	O
the	O
older	O
VM/SP	O
HPO	O
codebase	O
,	O
and	O
the	O
ESA/390	O
versions	O
are	O
based	O
on	O
the	O
newer	O
VM/XA	B-Application
codebase	O
.	O
</s>
<s>
z/VM	B-Application
,	O
the	O
last	O
version	O
still	O
widely	O
used	O
as	O
one	O
of	O
the	O
main	O
full	B-Architecture
virtualization	I-Architecture
solutions	O
for	O
the	O
mainframe	O
market	O
.	O
</s>
<s>
z/VM	B-Application
4.4	O
was	O
the	O
last	O
version	O
that	O
could	O
run	O
in	O
ESA/390	O
mode	O
;	O
subsequent	O
versions	O
only	O
run	O
in	O
z/Architecture	O
mode	O
.	O
</s>
<s>
The	O
CMS	O
in	O
the	O
name	O
refers	O
to	O
the	O
Conversational	B-Operating_System
Monitor	I-Operating_System
System	I-Operating_System
,	O
a	O
component	O
of	O
the	O
product	O
that	O
is	O
a	O
single-user	O
operating	B-General_Concept
system	I-General_Concept
that	O
runs	O
in	O
a	O
virtual	B-Architecture
machine	I-Architecture
and	O
provides	O
conversational	O
time-sharing	B-General_Concept
in	O
VM	O
.	O
</s>
<s>
The	O
heart	O
of	O
the	O
VM	O
architecture	O
is	O
the	O
Control	O
Program	O
or	O
hypervisor	B-Operating_System
abbreviated	O
CP	O
,	O
VM-CP	O
and	O
sometimes	O
,	O
ambiguously	O
,	O
VM	O
.	O
</s>
<s>
It	O
runs	O
on	O
the	O
physical	O
hardware	O
,	O
and	O
creates	O
the	O
virtual	B-Architecture
machine	I-Architecture
environment	O
.	O
</s>
<s>
VM-CP	O
provides	O
full	B-Architecture
virtualization	I-Architecture
of	O
the	O
physical	O
machine	O
–	O
including	O
all	O
I/O	O
and	O
other	O
privileged	O
operations	O
.	O
</s>
<s>
It	O
performs	O
the	O
system	O
's	O
resource-sharing	O
,	O
including	O
device	O
management	O
,	O
dispatching	O
,	O
virtual	B-Architecture
storage	I-Architecture
management	O
,	O
and	O
other	O
traditional	O
operating	B-General_Concept
system	I-General_Concept
tasks	O
.	O
</s>
<s>
Each	O
VM	O
user	O
is	O
provided	O
with	O
a	O
separate	O
virtual	B-Architecture
machine	I-Architecture
having	O
its	O
own	O
address	B-General_Concept
space	I-General_Concept
,	O
virtual	O
devices	O
,	O
etc.	O
,	O
and	O
which	O
is	O
capable	O
of	O
running	O
any	O
software	O
that	O
could	O
be	O
run	O
on	O
a	O
stand-alone	O
machine	O
.	O
</s>
<s>
A	O
given	O
VM	O
mainframe	O
typically	O
runs	O
hundreds	O
or	O
thousands	O
of	O
virtual	B-Architecture
machine	I-Architecture
instances	O
.	O
</s>
<s>
VM-CP	O
began	O
life	O
as	O
CP-370	O
,	O
a	O
reimplementation	O
of	O
CP-67	B-Application
,	O
itself	O
a	O
reimplementation	O
of	O
CP-40	B-Application
.	O
</s>
<s>
Running	O
within	O
each	O
virtual	B-Architecture
machine	I-Architecture
is	O
another	O
operating	B-General_Concept
system	I-General_Concept
,	O
a	O
guest	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
.	O
</s>
<s>
CMS	O
(	O
Conversational	B-Operating_System
Monitor	I-Operating_System
System	I-Operating_System
,	O
renamed	O
from	O
the	O
Cambridge	B-Operating_System
Monitor	I-Operating_System
System	I-Operating_System
of	O
CP/CMS	B-Application
)	O
.	O
</s>
<s>
Most	O
virtual	B-Architecture
machines	I-Architecture
run	O
CMS	O
,	O
a	O
lightweight	O
,	O
single-user	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
(	O
While	O
an	O
earlier	O
version	O
of	O
CMS	O
was	O
uncharitably	O
described	O
as	O
"	O
CP/M	B-Application
on	O
a	O
mainframe	O
"	O
,	O
the	O
comparison	O
is	O
an	O
anachronism	O
;	O
the	O
author	O
of	O
CP/M	B-Application
,	O
Gary	O
Kildall	O
,	O
was	O
an	O
experienced	O
CMS	O
user	O
.	O
)	O
</s>
<s>
GCS	O
(	O
Group	B-Application
Control	I-Application
System	I-Application
)	O
,	O
which	O
provides	O
a	O
limited	O
simulation	O
of	O
the	O
MVS	B-Application
API	O
.	O
</s>
<s>
IBM	O
originally	O
provided	O
GCS	O
in	O
order	O
to	O
run	O
VTAM	B-Application
without	O
a	O
service	O
OS/VS1	B-Application
virtual	B-Architecture
machine	I-Architecture
and	O
VTAM	B-Application
Communications	O
Network	O
Application	O
(	O
VCNA	O
)	O
.	O
</s>
<s>
RSCS	B-Application
V2	O
also	O
ran	O
under	O
GCS	O
.	O
</s>
<s>
A	O
mainstream	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
IBM	O
's	O
mainstream	O
operating	B-General_Concept
systems	I-General_Concept
(	O
i.e.	O
</s>
<s>
the	O
MVS	B-Application
,	O
DOS/VSE	B-Application
,	O
or	O
TSS/370	B-Application
families	O
)	O
can	O
be	O
loaded	O
and	O
run	O
without	O
modification	O
.	O
</s>
<s>
The	O
VM	O
hypervisor	B-Operating_System
treats	O
guest	B-General_Concept
operating	I-General_Concept
systems	I-General_Concept
as	O
application	O
programs	O
with	O
exceptional	O
privileges	O
–	O
it	O
prevents	O
them	O
from	O
directly	O
using	O
privileged	O
instructions	O
(	O
those	O
which	O
would	O
let	O
applications	O
take	O
over	O
the	O
whole	O
system	O
or	O
significant	O
parts	O
of	O
it	O
)	O
,	O
but	O
simulates	O
privileged	O
instructions	O
on	O
their	O
behalf	O
.	O
</s>
<s>
Most	O
mainframe	O
operating	B-General_Concept
systems	I-General_Concept
terminate	O
a	O
normal	O
application	O
which	O
tries	O
to	O
usurp	O
the	O
operating	B-General_Concept
system	I-General_Concept
's	O
privileges	O
.	O
</s>
<s>
The	O
VM	O
hypervisor	B-Operating_System
can	O
simulate	O
several	O
types	O
of	O
console	O
terminals	O
for	O
the	O
guest	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
,	O
such	O
as	O
the	O
hardcopy	O
line-mode	O
3215	O
,	O
the	O
graphical	O
3270	B-Operating_System
family	O
,	O
and	O
the	O
integrated	O
console	O
on	O
newer	O
System/390	B-Device
and	O
System	B-Device
Z	I-Device
machines	O
.	O
</s>
<s>
Other	O
users	O
can	O
then	O
access	O
running	O
virtual	B-Architecture
machines	I-Architecture
using	O
the	O
DIAL	O
command	O
at	O
the	O
logon	O
screen	O
,	O
which	O
will	O
connect	O
their	O
terminal	O
to	O
the	O
first	O
available	O
emulated	O
3270	B-Operating_System
device	O
,	O
or	O
the	O
first	O
available	O
2703	O
device	O
if	O
the	O
user	O
is	O
DIALing	O
from	O
a	O
typewriter	O
terminal	O
.	O
</s>
<s>
A	O
second	O
level	O
instance	O
of	O
VM	O
can	O
be	O
fully	O
virtualized	O
inside	O
a	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
This	O
technique	O
was	O
used	O
to	O
develop	O
S/370	B-Device
software	O
before	O
S/370	B-Device
hardware	O
was	O
available	O
,	O
and	O
it	O
has	O
continued	O
to	O
play	O
a	O
role	O
in	O
new	O
hardware	O
development	O
at	O
IBM	O
.	O
</s>
<s>
A	O
copy	O
of	O
the	O
mainframe	O
version	O
of	O
AIX	B-Application
or	O
Linux	B-Application
.	O
</s>
<s>
In	O
the	O
mainframe	O
environment	O
,	O
these	O
operating	B-General_Concept
systems	I-General_Concept
often	O
run	O
under	O
VM	O
,	O
and	O
are	O
handled	O
like	O
other	O
guest	B-General_Concept
operating	I-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
(	O
They	O
can	O
also	O
run	O
as	O
'	O
native	O
 '	O
operating	B-General_Concept
systems	I-General_Concept
on	O
the	O
bare	O
hardware	O
.	O
)	O
</s>
<s>
There	O
was	O
also	O
the	O
short-lived	O
IX/370	O
,	O
as	O
well	O
as	O
S/370	B-Device
and	O
S/390	B-Device
versions	O
of	O
AIX	B-Application
(	O
AIX/370	O
and	O
AIX/ESA	O
)	O
.	O
</s>
<s>
Several	O
non-CMS	O
systems	O
run	O
within	O
VM-CP	O
virtual	B-Architecture
machines	I-Architecture
,	O
providing	O
services	O
to	O
CMS	O
users	O
such	O
as	O
spooling	O
,	O
interprocess	O
communications	O
,	O
specialized	O
device	O
support	O
,	O
and	O
networking	O
.	O
</s>
<s>
By	O
running	O
in	O
separate	O
virtual	B-Architecture
machines	I-Architecture
,	O
they	O
receive	O
the	O
same	O
security	O
and	O
reliability	O
protections	O
as	O
other	O
VM	O
users	O
.	O
</s>
<s>
DIRMAINT	O
–	O
A	O
simplified	O
user	O
directory	O
management	O
system	O
(	O
the	O
directory	O
is	O
a	O
listing	O
of	O
every	O
account	O
on	O
the	O
system	O
,	O
including	O
virtual	B-General_Concept
hardware	I-General_Concept
configuration	O
,	O
user	O
passwords	O
,	O
and	O
minidisks	O
)	O
.	O
</s>
<s>
MUMPS/VM	O
—	O
an	O
implementation	O
of	O
the	O
MUMPS	B-Language
database	O
and	O
programming	O
language	O
which	O
could	O
run	O
as	O
guest	O
on	O
VM/370	O
.	O
</s>
<s>
MUMPS/VM	O
was	O
introduced	O
in	O
1987	O
and	O
discontinued	O
in	O
1991	O
.	O
</s>
<s>
A	O
user-written	O
or	O
modified	O
operating	B-General_Concept
system	I-General_Concept
,	O
such	O
as	O
National	O
CSS	B-Application
's	O
CSS	B-Application
or	O
Boston	O
University	O
's	O
VPS/VM	B-Application
.	O
</s>
<s>
IBM	O
coined	O
the	O
term	O
hypervisor	B-Operating_System
for	O
the	O
360/65	B-Device
and	O
later	O
used	O
it	O
for	O
the	O
DIAG	O
handler	O
of	O
CP-67	B-Application
.	O
</s>
<s>
IBM	O
repurposed	O
DIAG	O
for	O
"	O
communication	O
between	O
a	O
virtual	B-Architecture
machine	I-Architecture
and	O
CP.	O
"	O
</s>
<s>
At	O
one	O
time	O
,	O
CMS	O
was	O
capable	O
of	O
running	O
on	O
a	O
bare	O
machine	O
,	O
as	O
a	O
true	O
operating	B-General_Concept
system	I-General_Concept
(	O
though	O
such	O
a	O
configuration	O
would	O
be	O
unusual	O
)	O
.	O
</s>
<s>
This	O
is	O
because	O
CMS	O
relies	O
on	O
a	O
hypervisor	B-Operating_System
interface	O
to	O
VM-CP	O
,	O
to	O
perform	O
file	O
system	O
operations	O
and	O
request	O
other	O
VM	O
services	O
.	O
</s>
<s>
Was	O
first	O
developed	O
as	O
a	O
performance	O
improvement	O
for	O
CP/CMS	B-Application
release	O
2.1	O
,	O
an	O
important	O
early	O
milestone	O
in	O
CP	O
's	O
efficiency	O
.	O
</s>
<s>
CMS	O
and	O
other	O
operating	B-General_Concept
systems	I-General_Concept
often	O
have	O
DASD	O
requirements	O
much	O
smaller	O
than	O
the	O
sizes	O
of	O
actual	O
volumes	O
.	O
</s>
<s>
It	O
is	O
common	O
practice	O
to	O
define	O
full	O
volume	O
minidisks	O
for	O
use	O
by	O
such	O
guest	B-General_Concept
operating	I-General_Concept
systems	I-General_Concept
as	O
z/OS	B-Application
instead	O
of	O
using	O
DEDICATE	O
to	O
assign	O
the	O
volume	O
to	O
a	O
specific	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
The	O
SFS	O
is	O
provided	O
by	O
service	O
virtual	B-Architecture
machines	I-Architecture
.	O
</s>
<s>
The	O
CMS	O
user	O
virtual	B-Architecture
machines	I-Architecture
themselves	O
communicate	O
with	O
the	O
SFS	O
server	O
virtual	B-Architecture
machines	I-Architecture
through	O
the	O
IUCV	O
mechanism	O
.	O
</s>
<s>
The	O
early	O
history	O
of	O
VM	O
is	O
described	O
in	O
the	O
articles	O
CP/CMS	B-Application
and	O
History	B-Application
of	I-Application
CP/CMS	I-Application
.	O
</s>
<s>
VM/370	O
is	O
a	O
reimplementation	O
of	O
CP/CMS	B-Application
,	O
and	O
was	O
made	O
available	O
in	O
1972	O
as	O
part	O
of	O
IBM	O
's	O
System/370	B-Device
Advanced	O
Function	O
announcement	O
(	O
which	O
added	O
virtual	B-Architecture
memory	I-Architecture
hardware	O
and	O
operating	B-General_Concept
systems	I-General_Concept
to	O
the	O
System/370	B-Device
series	O
)	O
.	O
</s>
<s>
Early	O
releases	O
of	O
VM	O
through	O
VM/370	O
Release	O
6	O
continued	O
in	O
open	B-Application
source	I-Application
through	O
1981	O
,	O
and	O
today	O
are	O
considered	O
to	O
be	O
in	O
the	O
public	O
domain	O
.	O
</s>
<s>
As	O
with	O
CP-67	B-Application
,	O
privileged	O
instructions	O
in	O
a	O
virtual	B-Architecture
machine	I-Architecture
cause	O
a	O
program	O
interrupt	O
,	O
and	O
CP	O
simulated	O
the	O
behavior	O
of	O
the	O
privileged	O
instruction	O
.	O
</s>
<s>
VM	O
remained	O
an	O
important	O
platform	O
within	O
IBM	O
,	O
used	O
for	O
operating	B-General_Concept
system	I-General_Concept
development	O
and	O
time-sharing	B-General_Concept
use	O
;	O
but	O
for	O
customers	O
it	O
remained	O
IBM	O
's	O
"	O
other	O
operating	B-General_Concept
system	I-General_Concept
"	O
.	O
</s>
<s>
Those	O
that	O
did	O
formed	O
close	O
working	O
relationships	O
,	O
continuing	O
the	O
community-support	O
model	O
of	O
early	O
CP/CMS	B-Application
users	O
.	O
</s>
<s>
A	O
basic	O
problem	O
with	O
the	O
system	O
was	O
seen	O
at	O
IBM	O
's	O
field	O
sales	O
level	O
:	O
VM/CMS	O
demonstrably	O
reduced	O
the	O
amount	O
of	O
hardware	O
needed	O
to	O
support	O
a	O
given	O
number	O
of	O
time-sharing	B-General_Concept
users	O
.	O
</s>
<s>
Before	O
fifteen	O
years	O
had	O
passed	O
,	O
there	O
would	O
be	O
more	O
VM	O
licenses	O
than	O
MVS	B-Application
licenses.Varian	O
,	O
op	O
.	O
</s>
<s>
A	O
PC	B-Operating_System
DOS	I-Operating_System
version	O
that	O
runs	O
CMS	O
on	O
the	O
XT/370	O
(	O
and	O
later	O
on	O
the	O
AT/370	O
)	O
is	O
called	O
VM/PC	O
.	O
</s>
<s>
When	O
IBM	O
introduced	O
the	O
P/370	O
and	O
P/390	O
processor	O
cards	O
,	O
a	O
PC	O
could	O
now	O
run	O
full	O
VM	O
systems	O
,	O
including	O
VM/370	O
,	O
VM/SP	O
,	O
VM/XA	B-Application
,	O
and	O
VM/ESA	O
(	O
these	O
cards	O
were	O
fully	O
compatible	O
with	O
S/370	B-Device
and	O
S/390	B-Device
mainframes	O
,	O
and	O
could	O
run	O
any	O
S/370	B-Device
operating	B-General_Concept
system	I-General_Concept
from	O
the	O
31-bit	O
era	O
,	O
e.g.	O
,	O
MVS/ESA	O
,	O
VSE/ESA	O
)	O
.	O
</s>
<s>
With	O
VM/SP	O
HPO	O
installed	O
,	O
the	O
new	O
limit	O
was	O
64MB	O
;	O
however	O
,	O
a	O
single	O
user	O
(	O
or	O
virtual	B-Architecture
machine	I-Architecture
)	O
could	O
not	O
use	O
more	O
than	O
16MB	O
.	O
</s>
<s>
The	O
architecture	O
of	O
the	O
spool	O
filesystem	O
was	O
also	O
enhanced	O
,	O
each	O
spool	O
file	O
now	O
had	O
a	O
unique	O
user	O
ID	O
associated	O
with	O
it	O
,	O
and	O
reader	O
file	O
control	O
blocks	O
were	O
now	O
held	O
in	O
virtual	B-Architecture
storage	I-Architecture
.	O
</s>
<s>
System/370	B-Device
versions	O
of	O
VM	O
(	O
such	O
as	O
VM/SP	O
and	O
VM/SP	O
HPO	O
)	O
supported	O
a	O
maximum	O
of	O
two	O
processors	O
,	O
with	O
the	O
system	O
operating	O
in	O
either	O
UP	O
(	O
uniprocessor	O
)	O
mode	O
,	O
MP	O
(	O
multiprocessor	O
)	O
mode	O
,	O
or	O
AP	O
(	O
attached	O
processor	O
)	O
mode	O
.	O
</s>
<s>
System/370	B-Device
-XA	I-Device
releases	O
of	O
VM	O
(	O
such	O
as	O
VM/XA	B-Application
)	O
supported	O
more	O
.	O
</s>
<s>
System/390	B-Device
releases	O
(	O
such	O
as	O
VM/ESA	O
)	O
almost	O
removed	O
the	O
limit	O
entirely	O
,	O
and	O
some	O
modern	O
z/VM	B-Application
systems	O
can	O
have	O
as	O
many	O
as	O
80	O
processors	O
.	O
</s>
<s>
When	O
IBM	O
introduced	O
the	O
System/370	B-Device
Extended	O
Architecture	O
on	O
the	O
3081	B-Device
,	O
customers	O
were	O
faced	O
with	O
the	O
need	O
to	O
run	O
a	O
production	O
MVS/370	O
system	O
while	O
testing	O
MVS/XA	O
on	O
the	O
same	O
machine	O
.	O
</s>
<s>
IBM	O
's	O
solution	O
was	O
VM/XA	B-Application
Migration	O
Aid	O
,	O
which	O
used	O
the	O
new	O
Start	O
Interpretive	O
Execution	O
(	O
SIE	O
)	O
instruction	O
to	O
run	O
the	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
The	O
Processor	B-Device
Resource/System	I-Device
Manager	I-Device
(	O
PR/SM	B-Device
)	O
of	O
the	O
later	O
3090	B-Device
also	O
used	O
SIE	O
.	O
</s>
<s>
There	O
were	O
several	O
VM/XA	B-Application
products	O
before	O
it	O
was	O
eventually	O
supplanted	O
by	O
VM/ESA	O
and	O
z/VM	B-Application
.	O
</s>
<s>
In	O
addition	O
to	O
RSCS	B-Application
networking	O
,	O
IBM	O
also	O
provided	O
users	O
with	O
VTAM	B-Application
networking	O
.	O
</s>
<s>
ACF/VTAM	O
for	O
VM	O
was	O
fully	O
compatible	O
with	O
ACF/VTAM	O
on	O
MVS	B-Application
and	O
VSE	B-Application
.	O
</s>
<s>
Like	O
RSCS	B-Application
,	O
VTAM	B-Application
on	O
VM	O
ran	O
under	O
the	O
specialized	O
GCS	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
However	O
,	O
VM	O
also	O
supported	O
TCP/IP	B-Protocol
networking	O
.	O
</s>
<s>
In	O
the	O
late	O
1980s	O
,	O
IBM	O
produced	O
a	O
TCP/IP	B-Protocol
stack	I-Protocol
for	O
VM/SP	O
and	O
VM/XA	B-Application
.	O
</s>
<s>
The	O
stack	O
supported	O
IPv4	O
networks	O
,	O
and	O
a	O
variety	O
of	O
network	O
interface	O
systems	O
(	O
such	O
as	O
inter-mainframe	O
channel-to-channel	O
links	O
,	O
or	O
a	O
specialized	O
IBM	O
RT	O
PC	O
that	O
would	O
relay	O
traffic	O
out	O
to	O
a	O
Token	B-Device
Ring	I-Device
or	O
Ethernet	O
network	O
)	O
.	O
</s>
<s>
The	O
stack	O
provided	O
support	O
for	O
Telnet	B-Protocol
connections	O
,	O
from	O
either	O
simple	O
line-mode	O
terminal	O
emulators	O
or	O
VT100-compatible	O
emulators	O
,	O
or	O
proper	O
IBM	B-Operating_System
3270	I-Operating_System
terminal	O
emulators	O
.	O
</s>
<s>
PVM	O
,	O
like	O
VTAM	B-Application
,	O
allowed	O
for	O
connections	O
to	O
remote	O
VM/CMS	O
systems	O
,	O
as	O
well	O
as	O
other	O
IBM	O
systems	O
.	O
</s>
<s>
Later	O
releases	O
of	O
PVM	O
also	O
featured	O
a	O
component	O
that	O
could	O
accept	O
connections	O
from	O
a	O
SNA	B-Architecture
network	O
.	O
</s>
<s>
VM	O
was	O
also	O
the	O
cornerstone	O
operating	B-General_Concept
system	I-General_Concept
of	O
BITNET	B-General_Concept
,	O
as	O
the	O
RSCS	B-Application
system	O
available	O
for	O
VM	O
provided	O
a	O
simple	O
network	O
that	O
was	O
easy	O
to	O
implement	O
,	O
and	O
somewhat	O
reliable	O
.	O
</s>
<s>
VM	O
sites	O
were	O
interlinked	O
by	O
means	O
of	O
an	O
RSCS	B-Application
VM	O
on	O
each	O
VM	O
system	O
communicating	O
with	O
one	O
another	O
,	O
and	O
users	O
could	O
send	O
and	O
receive	O
messages	O
,	O
files	O
,	O
and	O
batch	O
jobs	O
through	O
RSCS	B-Application
.	O
</s>
<s>
The	O
"	O
NOTE	O
"	O
command	O
used	O
XEDIT	B-Application
to	O
display	O
a	O
dialog	O
to	O
create	O
an	O
email	O
,	O
from	O
which	O
the	O
user	O
could	O
send	O
it	O
.	O
</s>
<s>
If	O
the	O
user	O
specified	O
an	O
address	O
in	O
the	O
form	O
of	O
user	O
at	O
node	O
,	O
the	O
email	O
file	O
would	O
be	O
delivered	O
to	O
RSCS	B-Application
,	O
which	O
would	O
then	O
deliver	O
it	O
to	O
the	O
target	O
user	O
on	O
the	O
target	O
system	O
.	O
</s>
<s>
If	O
the	O
site	O
has	O
TCP/IP	B-Protocol
installed	O
,	O
RSCS	B-Application
could	O
work	O
with	O
the	O
SMTP	O
service	O
machine	O
to	O
deliver	O
notes	O
(	O
emails	O
)	O
to	O
remote	O
systems	O
,	O
as	O
well	O
as	O
receive	O
them	O
.	O
</s>
<s>
Backward	B-General_Concept
compatibility	I-General_Concept
remained	O
a	O
cornerstone	O
of	O
the	O
IBM	B-Device
mainframe	I-Device
family	O
,	O
which	O
still	O
uses	O
the	O
basic	O
instruction	O
set	O
introduced	O
with	O
the	O
original	O
System/360	B-Application
;	O
but	O
the	O
need	O
for	O
efficient	O
use	O
of	O
the	O
64-bit	O
zSeries	O
made	O
the	O
VM	O
approach	O
much	O
more	O
attractive	O
.	O
</s>
<s>
VM	O
was	O
also	O
utilized	O
in	O
data	O
centers	O
converting	O
from	O
DOS/VSE	B-Application
to	O
MVS	B-Application
and	O
is	O
useful	O
when	O
running	O
mainframe	O
AIX	B-Application
and	O
Linux	B-Application
,	O
platforms	O
that	O
were	O
to	O
become	O
increasingly	O
important	O
.	O
</s>
<s>
The	O
current	O
z/VM	B-Application
platform	O
has	O
finally	O
achieved	O
the	O
recognition	O
within	O
IBM	O
that	O
VM	O
users	O
long	O
felt	O
it	O
deserved	O
.	O
</s>
<s>
Some	O
z/VM	B-Application
sites	O
run	O
thousands	O
of	O
simultaneous	O
virtual	B-Architecture
machine	I-Architecture
users	O
on	O
a	O
single	O
system	O
.	O
</s>
<s>
z/VM	B-Application
was	O
first	O
released	O
in	O
October	O
2000	O
and	O
remains	O
in	O
active	O
use	O
and	O
development	O
.	O
</s>
<s>
Examples	O
include	O
RAMIS	B-Language
,	O
FOCUS	O
,	O
SPSS	B-Algorithm
,	O
NOMAD	B-Application
,	O
DB2	B-Application
,	O
REXX	B-Language
,	O
RACF	B-Application
,	O
and	O
OfficeVision	B-Application
.	O
</s>
<s>
Current	O
VM	O
offerings	O
run	O
the	O
gamut	O
of	O
mainframe	O
applications	O
,	O
including	O
HTTP	B-Protocol
servers	O
,	O
database	O
managers	O
,	O
analysis	O
tools	O
,	O
engineering	O
packages	O
,	O
and	O
financial	O
systems	O
.	O
</s>
<s>
As	O
of	O
release	O
6	O
,	O
the	O
VM/370	O
Control	O
Program	O
has	O
a	O
number	O
of	O
commands	O
for	O
General	O
Users	O
,	O
concerned	O
with	O
defining	O
and	O
controlling	O
the	O
user	O
's	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
Command	O
Description	O
#CP	O
Allows	O
the	O
user	O
to	O
issue	O
a	O
CP	O
command	O
from	O
a	O
command	O
environment	O
,	O
or	O
any	O
other	O
virtual	B-Architecture
machine	I-Architecture
after	O
pressing	O
the	O
break	O
key	O
(	O
defaults	O
to	O
PA1	O
)	O
ADSTOP	O
Sets	O
an	O
address	O
stop	O
to	O
halt	O
the	O
virtual	B-Architecture
machine	I-Architecture
at	O
a	O
specific	O
instruction	O
ATTN	O
Causes	O
an	O
attention	O
interruption	O
allowing	O
CP	O
to	O
take	O
control	O
in	O
a	O
command	O
environment	O
Begin	O
Continue	O
or	O
resume	O
execution	O
of	O
the	O
user	O
's	O
virtual	B-Architecture
machine	I-Architecture
,	O
optionally	O
at	O
a	O
specified	O
address	O
CHange	O
Alter	O
attributes	O
of	O
a	O
spool	O
file	O
or	O
files	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
output	O
class	O
or	O
the	O
name	O
of	O
the	O
file	O
can	O
be	O
changed	O
,	O
or	O
printer-specific	O
attributes	O
set	O
Close	O
Closes	O
an	O
open	O
printer	O
,	O
punch	O
,	O
reader	O
,	O
or	O
console	O
file	O
and	O
releases	O
it	O
to	O
the	O
spooling	O
system	O
COUPLE	O
Connect	O
a	O
virtual	O
channel-to-channel	B-Device
adapter	I-Device
(	O
CTCA	O
)	O
to	O
another	O
.	O
</s>
<s>
CP	O
Execute	O
a	O
CP	O
command	O
in	O
a	O
CMS	O
environment	O
DEFine	O
Alter	O
the	O
current	O
virtual	B-Architecture
machine	I-Architecture
configuration	O
.	O
</s>
<s>
Add	O
virtual	O
devices	O
or	O
change	O
available	O
storage	O
size	O
DETach	O
Remove	O
a	O
virtual	O
device	O
or	O
channel	O
from	O
the	O
current	O
configuration	O
DIAL	O
Connect	O
your	O
terminal	O
at	O
the	O
logon	O
screen	O
to	O
a	O
logged-on	O
multi-access	O
virtual	B-Architecture
machine	I-Architecture
's	O
simulated	O
3270	B-Operating_System
or	O
typewriter	O
terminals	O
DISConn	O
Disconnect	O
your	O
terminal	O
while	O
allowing	O
your	O
virtual	B-Architecture
machine	I-Architecture
to	O
continue	O
running	O
Display	O
Display	O
virtual	B-Architecture
machine	I-Architecture
storage	O
or	O
(	O
virtual	O
)	O
hardware	O
registers	O
DUMP	O
Print	O
a	O
snapshot	O
dump	O
of	O
the	O
current	O
virtual	B-Architecture
machine	I-Architecture
on	O
the	O
virtual	O
spooled	O
printer	O
ECHO	O
Set	O
the	O
virtual	B-Architecture
machine	I-Architecture
to	O
echo	O
typed	O
lines	O
EXTernal	O
Cause	O
an	O
external	O
interrupt	O
to	O
the	O
virtual	B-Architecture
machine	I-Architecture
INDicate	O
Display	O
current	O
system	O
load	O
or	O
your	O
resource	O
usage	O
Ipl	O
IPL	O
(	O
boot	O
)	O
an	O
operating	B-General_Concept
system	I-General_Concept
on	O
your	O
virtual	B-Architecture
machine	I-Architecture
LINK	O
Attach	O
a	O
device	O
from	O
another	O
virtual	B-Architecture
machine	I-Architecture
,	O
if	O
that	O
machine	O
's	O
definition	O
allows	O
sharing	O
LOADVFCB	O
Specify	O
a	O
forms	O
control	O
buffer	O
(	O
FCB	O
)	O
for	O
a	O
virtual	O
printer	O
LOGoffLOGout	O
Terminate	O
execution	O
of	O
the	O
current	O
virtual	B-Architecture
machine	I-Architecture
and	O
disconnect	O
from	O
the	O
system	O
LogonLogin	O
Sign	O
on	O
to	O
the	O
system	O
MessageMSG	O
Send	O
a	O
one-line	O
message	O
to	O
the	O
system	O
operator	O
or	O
another	O
user	O
NOTReady	O
Cause	O
a	O
virtual	O
device	O
to	O
appear	O
not	O
ready	O
ORDer	O
Reorder	O
closed	O
spool	O
files	O
by	O
ID	O
or	O
class	O
PURge	O
Delete	O
closed	O
spool	O
files	O
for	O
a	O
device	O
by	O
class	O
,	O
m	B-Language
ID	O
,	O
or	O
ALL	O
Query	O
Display	O
status	O
information	O
for	O
your	O
virtual	B-Architecture
machine	I-Architecture
,	O
or	O
the	O
message	O
of	O
the	O
day	O
,	O
or	O
number	O
or	O
names	O
of	O
logged-in	O
users	O
READY	O
Cause	O
a	O
device	O
end	O
interruption	O
for	O
a	O
device	O
REQuest	O
Cause	O
an	O
interrupt	O
on	O
your	O
virtual	O
console	O
RESET	O
Clear	O
all	O
pending	O
interrupts	O
for	O
a	O
device	O
REWind	O
Rewind	O
a	O
real	O
(	O
non	O
virtual	O
)	O
magnetic	O
tape	O
unit	O
SET	O
Set	O
various	O
attributes	O
for	O
your	O
virtual	B-Architecture
machine	I-Architecture
,	O
including	O
messaging	O
or	O
terminal	O
function	B-Application
keys	I-Application
SLeep	O
Place	O
your	O
virtual	B-Architecture
machine	I-Architecture
in	O
a	O
dormant	O
state	O
indefinitely	O
or	O
for	O
a	O
specified	O
period	O
of	O
time	O
SMsg	O
Send	O
a	O
one-line	O
special	O
message	O
to	O
another	O
virtual	B-Architecture
machine	I-Architecture
(	O
usually	O
used	O
to	O
control	O
the	O
operation	O
of	O
the	O
virtual	B-Architecture
machine	I-Architecture
;	O
commonly	O
used	O
with	O
RSCS	B-Application
)	O
SPool	O
Set	O
options	O
for	O
a	O
spooled	O
virtual	O
device	O
(	O
printer	O
,	O
reader	O
,	O
or	O
punch	O
)	O
STore	O
Alter	O
the	O
contents	O
of	O
registers	O
or	O
storage	O
of	O
your	O
virtual	B-Architecture
machine	I-Architecture
SYStem	O
Reset	O
or	O
restart	O
your	O
virtual	B-Architecture
machine	I-Architecture
or	O
clear	O
storage	O
TAg	O
Set	O
a	O
tag	O
associated	O
with	O
a	O
spooled	O
device	O
or	O
file	O
.	O
</s>
<s>
Unlike	O
the	O
normal	O
SFS	O
,	O
access	O
to	O
BFS	O
filesystems	O
is	O
controlled	O
by	O
POSIX	O
permissions	O
(	O
with	O
chmod	B-Application
and	O
chown	B-Device
)	O
.	O
</s>
<s>
Starting	O
with	O
z/VM	B-Application
Version	O
3	O
,	O
IBM	O
integrated	O
OpenEdition	O
into	O
z/VM	B-Application
and	O
renamed	O
it	O
OpenExtensions	O
.	O
</s>
<s>
Visual	O
editors	O
,	O
such	O
as	O
vi	B-Application
are	O
unavailable	O
,	O
as	O
3270	B-Operating_System
terminals	I-Operating_System
are	O
not	O
capable	O
.	O
</s>
<s>
Users	O
can	O
use	O
ed	B-Application
or	O
XEDIT	B-Application
instead	O
of	O
vi	B-Application
.	O
</s>
<s>
This	O
was	O
in	O
part	O
a	O
response	O
to	O
IBM	O
's	O
MVS	B-Application
users	O
selecting	O
the	O
turkey	O
as	O
a	O
mascot	O
(	O
chosen	O
,	O
according	O
to	O
legend	O
,	O
by	O
the	O
MVS	B-Application
Performance	O
Group	O
in	O
the	O
early	O
days	O
of	O
MVS	B-Application
,	O
when	O
its	O
performance	O
was	O
a	O
sore	O
topic	O
)	O
.	O
</s>
<s>
While	O
VM	O
was	O
relatively	O
light-weight	O
(	O
when	O
compared	O
to	O
its	O
counterparts	O
,	O
such	O
as	O
MVS	B-Application
)	O
,	O
VM	O
was	O
somewhat	O
unstable	O
in	O
its	O
early	O
days	O
.	O
</s>
<s>
Users	O
also	O
criticized	O
the	O
CMS	O
file	O
system	O
,	O
noting	O
that	O
other	O
operating	B-General_Concept
systems	I-General_Concept
in	O
the	O
mid-1980s	O
had	O
directories	O
,	O
symbolic	O
links	O
,	O
and	O
other	O
key	O
features	O
;	O
CMS	O
had	O
none	O
of	O
these	O
until	O
1988	O
when	O
VM/SP	O
release	O
6	O
came	O
out	O
,	O
which	O
introduced	O
the	O
Shared	O
File	O
System	O
and	O
alleviated	O
these	O
issues	O
.	O
</s>
