<s>
CP/CMS	B-Application
(	O
Control	O
Program/Cambridge	O
Monitor	O
System	O
)	O
is	O
a	O
discontinued	O
time-sharing	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
of	O
the	O
late	O
1960s	O
and	O
early	O
1970s	O
,	O
known	O
for	O
its	O
excellent	O
performance	O
and	O
advanced	O
features	O
.	O
</s>
<s>
CP-370/CMS	O
,	O
a	O
reimplementation	O
of	O
CP-67/CMS	O
for	O
the	O
System/370	B-Device
never	O
released	O
as	O
such	O
,	O
but	O
became	O
the	O
foundation	O
of	O
IBM	O
's	O
VM/370	B-Application
operating	B-General_Concept
system	I-General_Concept
,	O
announced	O
in	O
1972	O
.	O
</s>
<s>
CP-67/CMS	O
was	O
the	O
first	O
widely	O
available	O
virtual	B-Architecture
machine	I-Architecture
architecture	O
.	O
</s>
<s>
IBM	O
pioneered	O
this	O
idea	O
with	O
its	O
research	O
systems	O
M44/44X	B-Device
(	O
which	O
used	O
partial	B-General_Concept
virtualization	I-General_Concept
)	O
and	O
CP-40	B-Application
(	O
which	O
used	O
full	B-Architecture
virtualization	I-Architecture
)	O
.	O
</s>
<s>
In	O
addition	O
to	O
its	O
role	O
as	O
the	O
predecessor	O
of	O
the	O
VM	B-Application
family	O
,	O
CP/CMS	B-Application
played	O
an	O
important	O
role	O
in	O
the	O
development	O
of	O
operating	B-General_Concept
system	I-General_Concept
(	O
OS	O
)	O
theory	O
,	O
the	O
design	O
of	O
IBM	O
's	O
System/370	B-Device
,	O
the	O
time-sharing	B-General_Concept
industry	O
,	O
and	O
the	O
creation	O
of	O
a	O
self-supporting	O
user	O
community	O
that	O
anticipated	O
today	O
's	O
free	B-Application
software	I-Application
movement	O
.	O
</s>
<s>
Fundamental	O
CP/CMS	B-Application
architectural	O
and	O
strategic	O
parameters	O
were	O
established	O
in	O
CP-40	B-Application
,	O
which	O
began	O
production	O
use	O
at	O
IBM	O
's	O
Cambridge	O
Scientific	O
Center	O
in	O
early	O
1967	O
.	O
</s>
<s>
This	O
effort	O
occurred	O
in	O
a	O
complex	O
political	O
and	O
technical	O
milieu	O
,	O
discussed	O
at	O
some	O
length	O
and	O
supported	O
by	O
first-hand	O
quotes	O
in	O
the	O
Wikipedia	O
article	O
History	B-Application
of	I-Application
CP/CMS	I-Application
.	O
</s>
<s>
In	O
the	O
early	O
1960s	O
,	O
IBM	O
sought	O
to	O
maintain	O
dominance	O
over	O
scientific	O
computing	O
,	O
where	O
time-sharing	B-General_Concept
efforts	O
such	O
as	O
CTSS	B-Operating_System
and	O
MIT	O
's	O
Project	O
MAC	O
gained	O
focus	O
.	O
</s>
<s>
But	O
IBM	O
had	O
committed	O
to	O
a	O
huge	O
project	O
,	O
the	O
System/360	B-Application
,	O
which	O
took	O
the	O
company	O
in	O
a	O
different	O
direction	O
.	O
</s>
<s>
The	O
time-sharing	B-General_Concept
community	O
was	O
disappointed	O
with	O
the	O
S/360	B-Application
'	O
s	O
lack	O
of	O
time-sharing	B-General_Concept
capabilities	O
.	O
</s>
<s>
IBM	O
's	O
Cambridge	O
Scientific	O
Center	O
(	O
CSC	O
)	O
,	O
originally	O
established	O
to	O
support	O
Project	O
MAC	O
,	O
began	O
an	O
effort	O
to	O
regain	O
IBM	O
's	O
credibility	O
in	O
time-sharing	B-General_Concept
,	O
by	O
building	O
a	O
time-sharing	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
for	O
the	O
S/360	B-Application
.	O
</s>
<s>
This	O
system	O
would	O
eventually	O
become	O
CP/CMS	B-Application
.	O
</s>
<s>
In	O
the	O
same	O
spirit	O
,	O
IBM	O
designed	O
and	O
released	O
a	O
S/360	B-Application
model	O
with	O
time-sharing	B-General_Concept
features	O
,	O
the	O
IBM	B-Device
System/360	I-Device
-67	I-Device
,	O
and	O
a	O
time-sharing	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
,	O
TSS/360	B-Application
.	O
</s>
<s>
TSS	B-Application
failed	O
;	O
but	O
the	O
360-67	B-Device
and	O
CP/CMS	B-Application
succeeded	O
,	O
despite	O
internal	O
political	O
battles	O
over	O
time-sharing	B-General_Concept
,	O
and	O
concerted	O
efforts	O
at	O
IBM	O
to	O
scrap	O
the	O
CP/CMS	B-Application
effort	O
.	O
</s>
<s>
In	O
1967	O
,	O
CP/CMS	B-Application
production	O
use	O
began	O
,	O
first	O
on	O
CSC	O
's	O
CP-40	B-Application
,	O
then	O
later	O
on	O
CP-67	B-Application
at	O
Lincoln	O
Laboratories	O
and	O
other	O
sites	O
.	O
</s>
<s>
It	O
was	O
made	O
available	O
via	O
the	O
IBM	B-Application
Type-III	I-Application
Library	I-Application
in	O
1968	O
.	O
</s>
<s>
By	O
1972	O
,	O
CP/CMS	B-Application
had	O
gone	O
through	O
several	O
releases	O
;	O
it	O
was	O
a	O
robust	O
,	O
stable	O
system	O
running	O
on	O
44	O
systems	O
;	O
it	O
could	O
support	O
60	O
timesharing	B-General_Concept
users	O
on	O
a	O
S/360	B-Device
-67	I-Device
;	O
and	O
at	O
least	O
two	O
commercial	O
timesharing	B-General_Concept
vendors	O
(	O
National	O
CSS	O
and	O
IDC	O
)	O
were	O
reselling	O
S/360	B-Device
-67	I-Device
time	O
using	O
CP/CMS	B-Application
technology	O
.	O
</s>
<s>
In	O
1972	O
,	O
IBM	O
announced	O
the	O
addition	O
of	O
virtual	B-Architecture
memory	I-Architecture
to	O
the	O
S/370	B-Device
series	O
,	O
along	O
with	O
the	O
VM/370	B-Application
operating	B-General_Concept
system	I-General_Concept
,	O
a	O
reimplementation	O
of	O
CP/CMS	B-Application
for	O
the	O
S/370	B-Device
.	O
</s>
<s>
This	O
marked	O
the	O
end	O
of	O
CP/CMS	B-Application
releases	O
,	O
although	O
the	O
system	O
continued	O
its	O
independent	O
existence	O
for	O
some	O
time	O
.	O
</s>
<s>
VM	B-Application
releases	O
continued	O
to	O
include	O
source	O
code	O
for	O
some	O
time	O
and	O
members	O
of	O
the	O
VM	B-Application
community	O
long	O
remained	O
active	O
contributors	O
.	O
</s>
<s>
CP/CMS	B-Application
was	O
built	O
by	O
IBM	O
's	O
Cambridge	O
Scientific	O
Center	O
(	O
CSC	O
)	O
,	O
a	O
research	O
and	O
development	O
lab	O
with	O
ties	O
to	O
MIT	O
,	O
under	O
the	O
leadership	O
of	O
Robert	O
Creasy	O
.	O
</s>
<s>
The	O
system	O
's	O
goals	O
,	O
development	O
process	O
,	O
release	O
,	O
and	O
legacy	O
of	O
breakthrough	O
technology	O
,	O
set	O
this	O
system	O
apart	O
from	O
other	O
operating	B-General_Concept
systems	I-General_Concept
of	O
its	O
day	O
and	O
from	O
other	O
large	O
IBM	O
projects	O
.	O
</s>
<s>
It	O
was	O
an	O
open-source	B-Application
system	O
,	O
made	O
available	O
in	O
source	O
code	O
form	O
to	O
all	O
IBM	O
customers	O
at	O
no	O
charge	O
as	O
part	O
of	O
the	O
unsupported	O
IBM	B-Application
Type-III	I-Application
Library	I-Application
.	O
</s>
<s>
CP/CMS	B-Application
users	O
supported	O
themselves	O
and	O
each	O
other	O
.	O
</s>
<s>
CP/CMS	B-Application
consisted	O
of	O
two	O
main	O
components	O
:	O
</s>
<s>
CP	O
,	O
the	O
Control	O
Program	O
,	O
created	O
the	O
virtual	B-Architecture
machine	I-Architecture
environment	O
.	O
</s>
<s>
The	O
widely	O
used	O
version	O
was	O
CP-67	B-Application
,	O
ran	O
on	O
the	O
S/360	B-Device
-67	I-Device
.	O
</s>
<s>
(	O
The	O
research	O
system	O
CP-40	B-Application
established	O
the	O
architecture	O
.	O
</s>
<s>
A	O
third	O
version	O
,	O
CP-370	B-Application
,	O
became	O
VM/370	B-Application
.	O
)	O
</s>
<s>
Instead	O
of	O
explicitly	O
dividing	O
up	O
memory	O
and	O
other	O
resources	O
among	O
users	O
,	O
which	O
had	O
been	O
the	O
traditional	O
approach	O
,	O
CP	O
provided	O
each	O
user	O
with	O
a	O
simulated	O
stand-alone	O
System/360	B-Application
computer	O
.	O
</s>
<s>
Each	O
system	O
was	O
able	O
to	O
run	O
any	O
S/360	B-Application
software	O
that	O
ran	O
on	O
the	O
bare	O
machine	O
and	O
in	O
effect	O
gave	O
each	O
user	O
a	O
private	O
computer	O
system	O
.	O
</s>
<s>
CMS	O
,	O
the	O
Cambridge	B-Operating_System
Monitor	I-Operating_System
System	I-Operating_System
(	O
and	O
also	O
Console	O
Monitor	O
System	O
but	O
renamed	O
Conversational	B-Operating_System
Monitor	I-Operating_System
System	I-Operating_System
in	O
VM	B-Application
)	O
was	O
a	O
lightweight	O
single-user	O
operating	B-General_Concept
system	I-General_Concept
,	O
for	O
interactive	O
time-sharing	B-General_Concept
use	O
.	O
</s>
<s>
By	O
running	O
many	O
copies	O
of	O
CMS	O
in	O
CP	O
's	O
virtual	B-Architecture
machines	I-Architecture
instead	O
of	O
multiple	O
copies	O
of	O
large	O
,	O
traditional	O
multi-tasking	O
OS	O
the	O
overhead	O
per	O
user	O
was	O
less	O
.	O
</s>
<s>
This	O
allowed	O
a	O
great	O
number	O
of	O
simultaneous	O
users	O
to	O
share	O
a	O
single	O
S/360	B-Application
.	O
</s>
<s>
The	O
CP/CMS	B-Application
virtual	B-Architecture
machine	I-Architecture
concept	O
was	O
an	O
important	O
step	O
forward	O
in	O
operating	B-General_Concept
system	I-General_Concept
design	O
.	O
</s>
<s>
By	O
isolating	O
users	O
from	O
each	O
other	O
,	O
CP/CMS	B-Application
greatly	O
improved	O
system	O
reliability	O
and	O
security	O
.	O
</s>
<s>
By	O
simulating	O
a	O
full	O
,	O
stand-alone	O
computer	O
for	O
each	O
user	O
,	O
CP/CMS	B-Application
could	O
run	O
any	O
S/360	B-Application
software	O
in	O
a	O
time-sharing	B-General_Concept
environment	O
,	O
not	O
just	O
applications	O
specifically	O
designed	O
for	O
time-sharing	B-General_Concept
.	O
</s>
<s>
By	O
using	O
lightweight	O
CMS	O
as	O
the	O
primary	O
user	O
interface	O
,	O
CP/CMS	B-Application
achieved	O
unprecedented	O
time-sharing	B-General_Concept
performance	O
.	O
</s>
<s>
IBM	O
reimplemented	O
CP/CMS	B-Application
as	O
its	O
VM/370	B-Application
product	O
line	O
,	O
released	O
in	O
1972	O
when	O
virtual	B-Architecture
memory	I-Architecture
was	O
added	O
to	O
the	O
S/370	B-Device
series	O
.	O
</s>
<s>
VM/370	B-Application
'	O
s	O
successors	O
(	O
such	O
as	O
z/VM	B-Application
)	O
remain	O
in	O
wide	O
use	O
today	O
.	O
</s>
<s>
(	O
It	O
is	O
important	O
to	O
note	O
that	O
IBM	O
reimplemented	O
CP-67	B-Application
,	O
as	O
it	O
had	O
CP-40	B-Application
,	O
and	O
did	O
not	O
simply	O
rename	O
and	O
repackage	O
it	O
.	O
</s>
<s>
VM	B-Application
coexisted	O
with	O
CP/CMS	B-Application
and	O
its	O
successors	O
for	O
many	O
years	O
.	O
</s>
<s>
It	O
is	O
thus	O
appropriate	O
to	O
view	O
CP/CMS	B-Application
as	O
an	O
independent	O
OS	O
,	O
distinct	O
from	O
the	O
VM	B-Application
family	O
.	O
)	O
</s>
<s>
CP/CMS	B-Application
was	O
distributed	O
in	O
source	O
code	O
form	O
,	O
and	O
many	O
CP/CMS	B-Application
users	O
were	O
actively	O
involved	O
in	O
studying	O
and	O
modifying	O
that	O
source	O
code	O
.	O
</s>
<s>
Such	O
direct	O
user	O
involvement	O
with	O
a	O
vendor-supplied	O
operating	B-General_Concept
system	I-General_Concept
was	O
unusual	O
.	O
</s>
<s>
In	O
the	O
CP/CMS	B-Application
era	O
,	O
many	O
vendors	O
distributed	O
operating	B-General_Concept
systems	I-General_Concept
in	O
machine-readable	O
source	O
code	O
.	O
</s>
<s>
IBM	O
provided	O
optional	O
source	O
code	O
for	O
,	O
e.g.	O
,	O
OS/360	B-Application
,	O
DOS/360	O
,	O
several	O
later	O
mainstream	O
IBM	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
With	O
all	O
these	O
systems	O
,	O
some	O
awareness	O
of	O
system	O
source	O
code	O
was	O
also	O
involved	O
in	O
the	O
SYSGEN	B-Application
process	O
,	O
comparable	O
to	O
a	O
kernel	O
build	O
in	O
modern	O
systems	O
also	O
in	O
installing	O
a	O
Starter	O
Set	O
.	O
</s>
<s>
(	O
Forty	O
years	O
later	O
,	O
the	O
Hercules	B-Application
emulator	I-Application
can	O
be	O
used	O
to	O
run	O
fossilized	O
versions	O
of	O
these	O
systems	O
,	O
based	O
on	O
source	O
code	O
that	O
is	O
now	O
treated	O
as	O
part	O
of	O
the	O
public	O
domain	O
.	O
)	O
</s>
<s>
The	O
importance	O
of	O
operating	B-General_Concept
system	I-General_Concept
source	O
code	O
has	O
changed	O
over	O
time	O
.	O
</s>
<s>
For	O
complicated	O
reasons	O
,	O
CP/CMS	B-Application
was	O
not	O
released	O
in	O
the	O
normal	O
way	O
.	O
</s>
<s>
It	O
was	O
not	O
supported	O
by	O
IBM	O
,	O
but	O
was	O
made	O
part	O
of	O
the	O
unsupported	O
IBM	B-Application
Type-III	I-Application
Library	I-Application
,	O
a	O
collection	O
of	O
software	O
contributed	O
by	O
IBM	O
personnel	O
(	O
similarly	O
software	O
contributed	O
by	O
customers	O
formed	O
the	O
Type-IV	O
Library	O
)	O
.	O
</s>
<s>
CP/CMS	B-Application
and	O
other	O
Type-III	B-Application
products	I-Application
were	O
early	O
forms	O
of	O
free	B-Application
software	I-Application
.	O
</s>
<s>
Source	O
code	O
distribution	O
of	O
other	O
IBM	O
operating	B-General_Concept
systems	I-General_Concept
may	O
have	O
continued	O
for	O
some	O
time	O
(	O
e.g.	O
</s>
<s>
OS/360	B-Application
,	O
DOS/360	O
,	O
DOS/VSE	B-Application
,	O
MVS	B-Application
,	O
and	O
even	O
TSS/370	B-Application
,	O
which	O
all	O
today	O
are	O
generally	O
considered	O
to	O
be	O
in	O
the	O
public	O
domain	O
)	O
since	O
they	O
were	O
arguably	O
published	O
without	O
a	O
copyright	O
notice	O
before	O
1978.	O
}	O
</s>
<s>
However	O
,	O
the	O
unsupported	O
status	O
of	O
CP/CMS	B-Application
placed	O
different	O
pressures	O
on	O
its	O
user	O
community	O
and	O
created	O
the	O
need	O
for	O
source	O
code	O
distribution	O
.	O
</s>
<s>
CP/CMS	B-Application
was	O
contributed	O
to	O
the	O
Type-III	O
Library	O
by	O
MIT	O
's	O
Lincoln	O
Laboratory	O
and	O
not	O
by	O
IBM	O
,	O
despite	O
the	O
fact	O
that	O
the	O
system	O
was	O
built	O
by	O
IBM	O
's	O
Cambridge	O
Scientific	O
Center	O
.	O
</s>
<s>
This	O
decision	O
has	O
been	O
described	O
as	O
a	O
form	O
of	O
collusion	O
to	O
outmaneuver	O
the	O
IBM	O
political	O
forces	O
opposed	O
to	O
time-sharing	B-General_Concept
.	O
</s>
<s>
It	O
is	O
thought	O
that	O
it	O
may	O
also	O
reflect	O
the	O
amount	O
of	O
formal	O
and	O
informal	O
input	O
from	O
MIT	O
and	O
Union	O
Carbide	O
that	O
contributed	O
to	O
the	O
design	O
and	O
implementation	O
of	O
CP-40	B-Application
,	O
the	O
S/360	B-Device
-67	I-Device
,	O
CP-67	B-Application
,	O
and	O
CMS	O
.	O
</s>
<s>
See	O
History	B-Application
of	I-Application
CP/CMS	I-Application
(	O
historical	O
notes	O
)	O
for	O
further	O
insights	O
and	O
references	O
on	O
this	O
topic	O
.	O
</s>
<s>
Many	O
CP/CMS	B-Application
users	O
made	O
extensive	O
modifications	O
to	O
their	O
own	O
copies	O
of	O
the	O
source	O
code	O
.	O
</s>
<s>
Other	O
users	O
,	O
such	O
as	O
National	O
CSS	O
and	O
some	O
academic	O
sites	O
,	O
continued	O
independent	O
development	O
of	O
CP/CMS	B-Application
,	O
rather	O
than	O
switching	O
to	O
VM/370	B-Application
when	O
it	O
became	O
available	O
.	O
</s>
<s>
These	O
efforts	O
diverged	O
from	O
the	O
community	O
,	O
in	O
what	O
today	O
would	O
be	O
termed	O
a	O
software	B-Application
fork	I-Application
.	O
</s>
<s>
After	O
IBM	O
released	O
VM/370	B-Application
,	O
source	O
code	O
distribution	O
of	O
VM	B-Application
continued	O
for	O
several	O
releases	O
.	O
</s>
<s>
(	O
The	O
VM	B-Application
project	O
did	O
not	O
adopt	O
the	O
use	O
of	O
PL/S	B-Language
,	O
an	O
internal	O
systems	O
programming	O
language	O
mandated	O
for	O
use	O
within	O
IBM	O
on	O
many	O
comparable	O
projects	O
.	O
</s>
<s>
The	O
use	O
of	O
PL/S	B-Language
would	O
have	O
made	O
source	O
code	O
distribution	O
impossible	O
.	O
</s>
<s>
IBM	O
attempted	O
to	O
turn	O
away	O
from	O
assembly	O
language	O
to	O
higher	O
level	O
languages	O
as	O
early	O
as	O
1965	O
,	O
and	O
was	O
making	O
substantial	O
use	O
of	O
PL/S	B-Language
by	O
1969	O
,	O
e.g.	O
</s>
<s>
in	O
MVS	B-Application
.	O
</s>
<s>
PL/S	B-Language
was	O
considered	O
a	O
trade	O
secret	O
at	O
the	O
time	O
and	O
was	O
not	O
available	O
to	O
customers	O
.	O
</s>
<s>
The	O
VM	B-Application
user	O
community	O
continued	O
to	O
make	O
important	O
contributions	O
to	O
the	O
software	O
,	O
as	O
it	O
had	O
during	O
the	O
CP/CMS	B-Application
Type-III	O
period	O
.	O
</s>
<s>
Few	O
OS	O
or	O
DOS	O
sites	O
exhibited	O
active	O
user	O
involvement	O
in	O
deep	O
operating	B-General_Concept
system	I-General_Concept
internals	O
,	O
but	O
this	O
was	O
found	O
at	O
many	O
VM	B-Application
sites	O
.	O
</s>
<s>
This	O
reverse	O
support	O
helped	O
CP/CMS	B-Application
concepts	O
survive	O
and	O
evolve	O
,	O
despite	O
VM	B-Application
's	O
second	O
class	O
citizen	O
status	O
at	O
IBM	O
.	O
</s>
<s>
The	O
CP/CMS	B-Application
architecture	O
was	O
revolutionary	O
for	O
its	O
time	O
.	O
</s>
<s>
The	O
system	O
consisted	O
of	O
a	O
virtualizing	B-Application
control	I-Application
program	I-Application
(	O
CP	O
)	O
which	O
created	O
multiple	O
independent	O
virtual	B-Architecture
machines	I-Architecture
(	O
VMs	B-Application
)	O
.	O
</s>
<s>
Platform	B-General_Concept
virtualization	I-General_Concept
was	O
possible	O
because	O
of	O
two	O
elements	O
of	O
the	O
IBM	B-Device
System/360	I-Device
-67	I-Device
:	O
</s>
<s>
A	O
guest	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
,	O
which	O
would	O
run	O
in	O
"	O
supervisor	O
state	O
"	O
on	O
a	O
bare	O
machine	O
,	O
was	O
run	O
in	O
"	O
problem	O
state	O
"	O
under	O
CP	O
.	O
</s>
<s>
Each	O
virtual	B-Architecture
machine	I-Architecture
had	O
its	O
own	O
set	O
of	O
virtual	O
devices	O
,	O
mapped	O
from	O
the	O
system	O
's	O
real	O
hardware	O
environment	O
.	O
</s>
<s>
Thus	O
a	O
given	O
dial-up	O
teletype	O
was	O
presented	O
to	O
its	O
VM	B-Application
instance	O
as	O
its	O
virtual	O
console	O
.	O
</s>
<s>
Note	O
that	O
,	O
in	O
CP-67	B-Application
,	O
certain	O
model-dependent	O
and	O
diagnostic	O
instructions	O
were	O
not	O
virtualized	O
,	O
notably	O
the	O
DIAG	O
instruction	O
.	O
</s>
<s>
Ultimately	O
,	O
in	O
later	O
development	O
at	O
IBM	O
and	O
elsewhere	O
,	O
DIAG	O
instructions	O
were	O
used	O
to	O
create	O
a	O
non-virtualized	O
interface	O
,	O
to	O
what	O
became	O
called	O
a	O
hypervisor	B-Operating_System
.	O
</s>
<s>
Client	O
operating	B-General_Concept
systems	I-General_Concept
could	O
use	O
this	O
mechanism	O
to	O
communicate	O
directly	O
with	O
the	O
control	O
program	O
;	O
this	O
offered	O
dramatic	O
performance	O
improvements	O
.	O
</s>
<s>
Any	O
S/360	B-Application
operating	B-General_Concept
system	I-General_Concept
could	O
in	O
fact	O
be	O
run	O
under	O
CP	O
,	O
but	O
normal	O
users	O
ran	O
Cambridge	B-Operating_System
Monitor	I-Operating_System
System	I-Operating_System
(	O
CMS	O
)	O
,	O
a	O
simple	O
,	O
single-user	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
CP-67	B-Application
versions	O
1	O
and	O
2	O
did	O
not	O
support	O
virtual	B-Architecture
memory	I-Architecture
inside	O
a	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
At	O
that	O
point	O
,	O
testing	O
and	O
development	O
of	O
CP	O
itself	O
could	O
be	O
done	O
by	O
running	O
a	O
full	O
copy	O
of	O
CP/CMS	B-Application
inside	O
a	O
single	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
Some	O
CP/CMS	B-Application
operating	B-General_Concept
system	I-General_Concept
work	O
,	O
such	O
as	O
CP-370	B-Application
development	O
and	O
MVS	B-Application
testing	O
,	O
ran	O
four	O
-	O
or	O
five-level	O
deep	O
stacks	O
of	O
hardware	O
and	O
OS	O
simulations	O
.	O
</s>
<s>
The	O
CP/CMS	B-Application
design	O
is	O
different	O
from	O
IBM	O
's	O
previous	O
monolithic	B-Architecture
operating	I-Architecture
systems	I-Architecture
,	O
it	O
separates	O
complex	O
"	O
big	O
system	O
"	O
(	O
dispatching	O
,	O
hardware	O
management	O
,	O
mass	O
storage	O
)	O
from	O
"	O
little	O
system	O
"	O
(	O
application	O
program	O
execution	O
,	O
file	O
I/O	O
,	O
console	O
input/output	O
)	O
.	O
</s>
<s>
This	O
is	O
a	O
model	O
feature	O
in	O
microkernel	B-Operating_System
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
IBM	O
's	O
decision	O
to	O
implement	O
virtualization	B-Application
and	O
virtual	B-Architecture
memory	I-Architecture
features	O
in	O
the	O
subsequent	O
S/370	B-Device
design	O
(	O
although	O
missing	O
from	O
the	O
initial	O
S/370	B-Device
series	O
)	O
reflects	O
,	O
at	O
least	O
in	O
part	O
,	O
the	O
success	O
of	O
the	O
CP/CMS	B-Application
approach	O
.	O
</s>
<s>
In	O
turn	O
the	O
survival	O
and	O
success	O
of	O
IBM	O
's	O
VM	B-Application
operating	I-Application
system	I-Application
family	O
,	O
and	O
of	O
virtualization	B-General_Concept
technology	I-General_Concept
in	O
general	O
,	O
owe	O
much	O
to	O
the	O
S/360	B-Device
-67	I-Device
.	O
</s>
<s>
In	O
many	O
respects	O
,	O
IBM	O
's	O
CP-67	B-Application
and	O
CP/CMS	B-Application
products	O
anticipated	O
(	O
and	O
heavily	O
influenced	O
)	O
contemporary	O
virtualization	B-Application
software	I-Application
,	O
such	O
as	O
VMware	O
Workstation	O
,	O
Xen	B-Operating_System
,	O
and	O
Microsoft	B-Application
Virtual	I-Application
PC	I-Application
.	O
</s>
<s>
CP-40	B-Application
and	O
CP-67	B-Application
were	O
implementations	O
for	O
CSC	O
's	O
customized	O
S/360	B-Application
-40	O
and	O
the	O
standard	O
S/360	B-Device
-67	I-Device
,	O
respectively	O
.	O
</s>
<s>
CMS	O
:	O
Cambridge	B-Operating_System
Monitor	I-Operating_System
System	I-Operating_System
.	O
</s>
<s>
This	O
portion	O
of	O
the	O
CP/CMS	B-Application
system	O
was	O
renamed	O
Conversational	B-Operating_System
Monitor	I-Operating_System
System	I-Operating_System
when	O
IBM	O
released	O
VM/370	B-Application
.	O
</s>
<s>
Unlike	O
the	O
CP-to-VM	O
transition	O
,	O
however	O
,	O
which	O
was	O
a	O
reimplementation	O
,	O
much	O
of	O
CMS	O
was	O
moved	O
without	O
modification	O
from	O
CP/CMS	B-Application
into	O
VM/370	B-Application
.	O
</s>
<s>
VM	B-Application
:	O
Virtual	B-Architecture
Machine	I-Architecture
,	O
initially	O
the	O
term	O
pseudo-machine	O
was	O
used	O
,	O
but	O
soon	O
virtual	B-Architecture
machine	I-Architecture
was	O
borrowed	O
from	O
the	O
IBM	B-Device
M44/44X	I-Device
project	O
.	O
</s>
<s>
It	O
was	O
well	O
established	O
in	O
CP/CMS	B-Application
by	O
the	O
time	O
IBM	O
introduced	O
VM/370	B-Application
.	O
</s>
<s>
hypervisor	B-Operating_System
:	O
a	O
mechanism	O
for	O
paravirtualization	O
.	O
</s>
<s>
This	O
term	O
was	O
coined	O
in	O
IBM	O
's	O
reimplementation	O
of	O
CP-67	B-Application
as	O
VM/370	B-Application
.	O
</s>
