<s>
The	O
Conversational	B-Operating_System
Monitor	I-Operating_System
System	I-Operating_System
(	O
CMS	O
originally	O
:	O
"	O
Cambridge	B-Operating_System
Monitor	I-Operating_System
System	I-Operating_System
"	O
)	O
is	O
a	O
simple	O
interactive	B-General_Concept
single-user	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
CMS	O
was	O
originally	O
developed	O
as	O
part	O
of	O
IBM	O
's	O
CP/CMS	B-Application
operating	B-General_Concept
system	I-General_Concept
,	O
which	O
went	O
into	O
production	O
use	O
in	O
1967	O
.	O
</s>
<s>
CMS	O
is	O
part	O
of	O
IBM	O
's	O
VM	B-Application
family	I-Application
,	O
which	O
runs	O
on	O
IBM	B-Device
mainframe	I-Device
computers	O
.	O
</s>
<s>
VM	B-Application
was	O
first	O
announced	O
in	O
1972	O
,	O
and	O
is	O
still	O
in	O
use	O
today	O
as	O
z/VM	B-Application
.	O
</s>
<s>
CMS	O
runs	O
as	O
a	O
"	O
guest	O
"	O
operating	B-General_Concept
system	I-General_Concept
in	O
a	O
private	O
virtual	B-Architecture
machine	I-Architecture
created	O
by	O
the	O
VM	B-Application
control	O
program	O
.	O
</s>
<s>
The	O
control	O
program	O
plus	O
CMS	O
together	O
create	O
a	O
multi-user	O
time-sharing	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
.	O
</s>
<s>
CMS	O
was	O
originally	O
developed	O
as	O
part	O
of	O
IBM	O
's	O
CP/CMS	B-Application
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
At	O
the	O
time	O
,	O
the	O
acronym	O
meant	O
"	O
Cambridge	B-Operating_System
Monitor	I-Operating_System
System	I-Operating_System
"	O
(	O
but	O
also	O
:	O
"	O
Console	O
Monitor	O
System	O
"	O
)	O
.	O
</s>
<s>
CMS	O
first	O
ran	O
under	O
CP-40	B-Application
,	O
a	O
one-off	O
research	O
system	O
using	O
custom	O
hardware	O
at	O
IBM	O
's	O
Cambridge	O
Scientific	O
Center	O
.	O
</s>
<s>
The	O
CMS	O
user	O
interface	O
drew	O
heavily	O
on	O
experience	O
with	O
the	O
influential	O
first-generation	O
time-sharing	B-General_Concept
system	I-General_Concept
CTSS	B-Operating_System
,	O
some	O
of	O
whose	O
developers	O
worked	O
on	O
CP/CMS	B-Application
.	O
</s>
<s>
(	O
CTSS	B-Operating_System
was	O
used	O
as	O
an	O
early	O
CP/CMS	B-Application
development	O
platform	O
.	O
)	O
</s>
<s>
Later	O
in	O
1967	O
,	O
CP/CMS	B-Application
became	O
generally	O
available	O
on	O
the	O
IBM	B-Device
System/360	I-Device
Model	I-Device
67	I-Device
,	O
where	O
,	O
although	O
the	O
new	O
control	O
program	O
CP-67	B-Application
was	O
a	O
substantial	O
re-implementation	O
of	O
CP-40	B-Application
,	O
CMS	O
remained	O
essentially	O
the	O
same	O
.	O
</s>
<s>
IBM	O
provided	O
CP/CMS	B-Application
"	O
as	O
is	O
"	O
without	O
any	O
support	O
,	O
in	O
source	O
code	O
form	O
,	O
as	O
part	O
of	O
the	O
IBM	B-Application
Type-III	I-Application
Library	I-Application
.	O
</s>
<s>
CP/CMS	B-Application
was	O
thus	O
an	O
open	B-Application
source	I-Application
system	O
.	O
</s>
<s>
Despite	O
this	O
lack	O
of	O
support	O
from	O
IBM	O
,	O
CP/CMS	B-Application
achieved	O
great	O
success	O
as	O
a	O
time-sharing	B-General_Concept
platform	O
;	O
by	O
1972	O
,	O
there	O
were	O
some	O
44	O
CP/CMS	B-Application
systems	O
in	O
use	O
,	O
including	O
commercial	O
sites	O
that	O
resold	O
access	O
to	O
CP/CMS	B-Application
.	O
</s>
<s>
In	O
1972	O
,	O
IBM	O
released	O
its	O
VM/370	B-Application
operating	B-General_Concept
system	I-General_Concept
,	O
a	O
re-implementation	O
of	O
CP/CMS	B-Application
for	O
the	O
System/370	B-Device
,	O
in	O
an	O
announcement	O
that	O
also	O
added	O
virtual	B-Architecture
memory	I-Architecture
hardware	O
to	O
the	O
System/370	B-Device
series	O
.	O
</s>
<s>
Unlike	O
CP/CMS	B-Application
,	O
VM/370	B-Application
was	O
supported	O
by	O
IBM	O
.	O
</s>
<s>
VM	B-Application
went	O
through	O
a	O
series	O
of	O
versions	O
,	O
and	O
is	O
still	O
in	O
use	O
today	O
as	O
z/VM	B-Application
.	O
</s>
<s>
Through	O
all	O
its	O
distinct	O
versions	O
and	O
releases	O
,	O
the	O
CMS	O
platform	O
remained	O
still	O
quite	O
recognizable	O
as	O
a	O
close	O
descendant	O
of	O
the	O
original	O
CMS	O
version	O
running	O
under	O
CP-40	B-Application
.	O
</s>
<s>
Many	O
key	O
user	O
interface	O
decisions	O
familiar	O
to	O
today	O
's	O
users	O
had	O
already	O
been	O
made	O
in	O
1965	O
,	O
as	O
part	O
of	O
the	O
CP-40	B-Application
effort	O
.	O
</s>
<s>
See	O
CMS	O
under	O
CP-40	B-Application
for	O
examples	O
.	O
</s>
<s>
Both	O
VM	B-Application
and	O
CP/CMS	B-Application
had	O
checkered	O
histories	O
at	O
IBM	O
.	O
</s>
<s>
VM	B-Application
was	O
not	O
one	O
of	O
IBM	O
's	O
"	O
strategic	O
"	O
operating	B-General_Concept
systems	I-General_Concept
,	O
which	O
were	O
primarily	O
the	O
OS	B-Application
and	O
DOS	O
families	O
,	O
and	O
it	O
suffered	O
from	O
IBM	O
political	O
infighting	O
over	O
time-sharing	B-General_Concept
versus	O
batch	B-General_Concept
processing	I-General_Concept
goals	O
.	O
</s>
<s>
This	O
conflict	O
is	O
why	O
CP/CMS	B-Application
was	O
originally	O
released	O
as	O
an	O
unsupported	O
system	O
,	O
and	O
why	O
VM	B-Application
often	O
had	O
limited	O
development	O
and	O
support	O
resources	O
within	O
IBM	O
.	O
</s>
<s>
An	O
exceptionally	O
strong	O
user	O
community	O
,	O
first	O
established	O
in	O
the	O
self-support	O
days	O
of	O
CP/CMS	B-Application
but	O
remaining	O
active	O
after	O
the	O
launch	O
of	O
VM	B-Application
,	O
made	O
substantial	O
contributions	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
and	O
mitigated	O
the	O
difficulties	O
of	O
running	O
IBM	O
's	O
"	O
other	O
operating	B-General_Concept
system	I-General_Concept
"	O
.	O
</s>
<s>
CMS	O
is	O
an	O
intrinsic	O
part	O
of	O
the	O
VM/CMS	B-Application
architecture	O
,	O
established	O
with	O
CP/CMS	B-Application
.	O
</s>
<s>
Each	O
CMS	O
user	O
has	O
control	O
over	O
a	O
private	O
virtual	B-Architecture
machine	I-Architecture
a	O
simulated	O
copy	O
of	O
the	O
underlying	O
physical	O
computer	O
in	O
which	O
CMS	O
runs	O
as	O
a	O
stand-alone	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
More	O
details	O
on	O
how	O
CMS	O
interacts	O
with	O
the	O
virtual	B-Architecture
machine	I-Architecture
environment	O
can	O
be	O
found	O
in	O
the	O
VM	B-Application
and	O
CP/CMS	B-Application
articles	O
.	O
</s>
<s>
CMS	O
was	O
originally	O
built	O
as	O
a	O
stand-alone	O
operating	B-General_Concept
system	I-General_Concept
,	O
capable	O
of	O
running	O
on	O
a	O
bare	O
machine	O
(	O
though	O
of	O
course	O
nobody	O
would	O
choose	O
to	O
do	O
so	O
)	O
.	O
</s>
<s>
However	O
,	O
CMS	O
can	O
no	O
longer	O
run	O
outside	O
the	O
VM	B-Application
environment	O
,	O
which	O
provides	O
the	O
hypervisor	B-Operating_System
interface	O
needed	O
for	O
various	O
critical	O
functions	O
.	O
</s>
<s>
CMS	O
provides	O
users	O
an	O
environment	O
for	O
running	O
applications	B-Application
or	O
batch	B-General_Concept
jobs	I-General_Concept
,	O
managing	O
data	B-Operating_System
files	I-Operating_System
,	O
creating	O
and	O
debugging	O
applications	B-Application
,	O
doing	O
cross-platform	B-Operating_System
development	O
,	O
and	O
communicating	O
with	O
other	O
systems	O
or	O
users	O
.	O
</s>
<s>
Users	O
log	O
into	O
VM	B-Application
,	O
providing	O
a	O
userid	O
and	O
password	O
,	O
and	O
then	O
boot	B-Operating_System
their	O
own	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
This	O
can	O
be	O
done	O
by	O
issuing	O
the	O
command	O
"	O
IPL	O
CMS	O
"	O
(	O
"	O
IPL	O
"	O
=	O
initial	O
program	O
load	O
,	O
traditional	O
IBM	O
jargon	O
for	O
booting	B-Operating_System
a	O
machine	O
)	O
;	O
though	O
this	O
is	O
normally	O
done	O
automatically	O
for	O
the	O
user	O
.	O
</s>
<s>
By	O
the	O
late	O
1970s	O
,	O
however	O
,	O
most	O
VM	B-Application
users	O
were	O
connecting	O
via	O
full-screen	O
terminals	O
particularly	O
the	O
IBM	B-Operating_System
3270	I-Operating_System
,	O
the	O
ubiquitous	O
transaction	B-General_Concept
processing	I-General_Concept
terminal	O
on	O
IBM	B-Device
mainframes	I-Device
.	O
</s>
<s>
The	O
3270	B-Operating_System
played	O
a	O
strategic	O
role	O
in	O
IBM	O
's	O
product	O
line	O
,	O
making	O
its	O
selection	O
a	O
natural	O
choice	O
for	O
large	O
data	O
centers	O
of	O
the	O
day	O
.	O
</s>
<s>
Many	O
other	O
manufacturers	O
eventually	O
offered	O
bisync	B-Protocol
terminals	O
that	O
emulated	O
the	O
3270	B-Operating_System
protocol	O
.	O
</s>
<s>
3270s	B-Operating_System
had	O
local	O
buffer	O
storage	O
,	O
some	O
processing	O
capabilities	O
,	O
and	O
generally	O
dealt	O
with	O
an	O
entire	O
screen	O
of	O
data	O
at	O
a	O
time	O
.	O
</s>
<s>
They	O
handled	O
editing	O
tasks	O
locally	O
,	O
and	O
then	O
transmitted	O
a	O
set	O
of	O
fields	O
(	O
or	O
the	O
entire	O
page	O
)	O
at	O
once	O
when	O
the	O
ENTER	O
key	O
or	O
a	O
program	B-Application
function	I-Application
key	I-Application
(	O
PFK	O
)	O
was	O
pressed	O
.	O
</s>
<s>
The	O
3270	B-Operating_System
family	O
incorporated	O
"	O
smart	O
"	O
control	O
units	O
,	O
concentrators	O
,	O
and	O
other	O
network	O
processing	O
elements	O
,	O
communicating	O
with	O
the	O
mainframe	O
over	O
dedicated	O
circuits	O
at	O
relatively	O
high	O
speeds	O
,	O
via	O
a	O
bisync	B-Protocol
synchronous	O
communication	O
protocol	O
.	O
</s>
<s>
(	O
These	O
mainframe-oriented	O
communication	O
technologies	O
provided	O
some	O
of	O
the	O
capabilities	O
taken	O
for	O
granted	O
in	O
modern	O
communication	O
networks	O
,	O
such	O
as	O
device	O
addressing	O
,	O
routing	O
,	O
error	O
correction	O
,	O
and	O
support	O
for	O
a	O
variety	O
of	O
configurations	O
such	O
as	O
multipoint	O
and	O
multidrop	B-Architecture
topologies	O
.	O
)	O
</s>
<s>
The	O
3270	B-Operating_System
approach	O
differed	O
from	O
lower-cost	O
dumb	O
terminals	O
of	O
the	O
period	O
,	O
which	O
were	O
point-to-point	O
and	O
asynchronous	O
.	O
</s>
<s>
Commercial	O
time-sharing	B-General_Concept
users	O
,	O
an	O
important	O
segment	O
of	O
early	O
CP/CMS	B-Application
and	O
VM	B-Application
sites	O
,	O
relied	O
on	O
such	O
devices	O
because	O
they	O
could	O
connect	O
via	O
300	O
-	O
or	O
1200	O
bit/s	O
modems	O
over	O
normal	O
voice-grade	O
telephone	O
circuits	O
.	O
</s>
<s>
Installing	O
a	O
dedicated	O
circuit	O
for	O
a	O
3270	B-Operating_System
was	O
often	O
not	O
practical	O
,	O
economical	O
,	O
or	O
timely	O
.	O
</s>
<s>
The	O
3270	B-Operating_System
's	O
block-oriented	O
approach	O
was	O
more	O
consistent	O
with	O
IBM	O
's	O
batch	O
-	O
and	O
punched	O
card-oriented	O
view	O
of	O
computing	O
,	O
and	O
was	O
particularly	O
important	O
for	O
IBM	B-Device
mainframes	I-Device
of	O
the	O
day	O
.	O
</s>
<s>
Unlike	O
contemporary	O
minicomputers	O
,	O
most	O
IBM	B-Device
mainframes	I-Device
were	O
not	O
equipped	O
for	O
character-at-a-time	O
interrupts	O
.	O
</s>
<s>
Dumb	O
terminal	O
support	O
relied	O
on	O
terminal	O
control	O
units	O
such	O
as	O
the	O
IBM	B-Device
270x	I-Device
(	O
see	O
IBM	B-Device
3705	I-Device
)	O
or	O
Memorex	O
1270	O
.	O
</s>
<s>
The	O
3270	B-Operating_System
approach	O
was	O
preferred	O
.	O
)	O
</s>
<s>
Block-oriented	O
terminals	O
like	O
the	O
3270	B-Operating_System
made	O
it	O
practical	O
to	O
implement	O
screen-oriented	B-Application
editors	I-Application
on	O
mainframes	O
as	O
opposed	O
to	O
line-oriented	B-Application
editors	I-Application
,	O
the	O
previous	O
norm	O
.	O
</s>
<s>
This	O
had	O
been	O
an	O
important	O
advantage	O
of	O
contemporary	O
minicomputers	O
and	O
other	O
character-oriented	O
systems	O
,	O
and	O
its	O
availability	O
via	O
the	O
3270	B-Operating_System
was	O
warmly	O
welcomed	O
.	O
</s>
<s>
A	O
gulf	O
developed	O
between	O
the	O
3270	B-Operating_System
world	O
,	O
focused	O
on	O
page-oriented	O
mainframe	O
transaction	B-General_Concept
processing	I-General_Concept
(	O
especially	O
via	O
CICS	B-Application
)	O
,	O
and	O
the	O
asynch	O
terminal	O
world	O
,	O
focused	O
on	O
character-oriented	O
minicomputers	O
and	O
dial-up	O
timesharing	B-General_Concept
.	O
</s>
<s>
However	O
,	O
these	O
devices	O
rarely	O
competed	O
for	O
3270	B-Operating_System
users	O
;	O
IBM	O
maintained	O
its	O
dominance	O
over	O
mainframe	O
data	O
center	O
hardware	O
purchase	O
decisions	O
.	O
</s>
<s>
Asynchronous	O
terminal	O
controllers	O
and	O
3270s	B-Operating_System
both	O
provided	O
the	O
mainframe	O
with	O
block-oriented	O
interactions	O
essentially	O
,	O
they	O
made	O
the	O
terminal	O
input	O
look	O
like	O
a	O
card	O
reader	O
.	O
</s>
<s>
The	O
difference	O
is	O
apparent	O
when	O
comparing	O
the	O
atomic	B-General_Concept
transaction	I-General_Concept
approach	O
of	O
dominant	O
CICS	B-Application
with	O
the	O
interactive	B-General_Concept
,	O
stream-oriented	O
style	O
of	O
UNIX	B-Application
.	O
</s>
<s>
VM/CMS	B-Application
evolved	O
somewhere	O
between	O
these	O
extremes	O
.	O
</s>
<s>
CMS	O
has	O
a	O
command-driven	O
,	O
stateful	B-Application
,	O
interactive	B-General_Concept
environment	O
,	O
rather	O
than	O
adopting	O
the	O
CICS	B-Application
approach	O
of	O
a	O
stateless	B-Protocol
transaction-oriented	B-General_Concept
interface	O
.	O
</s>
<s>
CMS	O
earned	O
a	O
very	O
good	O
reputation	O
for	O
being	O
efficient	O
,	O
and	O
for	O
having	O
good	O
human	O
factors	O
for	O
ease	O
of	O
use	O
,	O
relative	O
to	O
the	O
standards	O
of	O
the	O
time	O
(	O
and	O
of	O
course	O
prior	O
to	O
widespread	O
use	O
of	O
graphical	B-Application
user	I-Application
interface	I-Application
environments	O
such	O
as	O
are	O
commonly	O
used	O
today	O
)	O
.	O
</s>
<s>
It	O
was	O
not	O
uncommon	O
to	O
have	O
hundreds	O
(	O
later	O
:	O
thousands	O
)	O
of	O
concurrent	O
CMS	O
interactive	B-General_Concept
users	O
on	O
the	O
same	O
VM	B-Application
mainframe	O
,	O
with	O
sub-second	O
response	O
times	O
for	O
common	O
,	O
'	O
trivial	O
 '	O
functions	O
.	O
</s>
<s>
VM/CMS	B-Application
consistently	O
outperformed	O
MVS	B-Application
and	O
other	O
IBM	O
operating	B-General_Concept
systems	I-General_Concept
in	O
terms	O
of	O
support	O
for	O
simultaneous	O
interactive	B-General_Concept
users	O
.	O
</s>
<s>
Many	O
CMS	O
users	O
programmed	O
in	O
such	O
languages	O
as	O
COBOL	B-Application
,	O
FORTRAN	B-Application
,	O
PL/I	B-Language
,	O
C/370	B-Language
,	O
APL	B-Language
,	O
and	O
the	O
scripting	O
language	O
REXX	B-Language
.	O
</s>
<s>
VM/CMS	B-Application
was	O
often	O
used	O
as	O
a	O
development	O
platform	O
for	O
production	O
systems	O
that	O
ran	O
under	O
IBM	O
's	O
other	O
operating	B-General_Concept
systems	I-General_Concept
,	O
such	O
as	O
MVS	B-Application
.	O
</s>
<s>
Other	O
CMS	O
users	O
worked	O
with	O
commercial	O
software	O
packages	O
such	O
as	O
FOCUS	O
,	O
NOMAD	B-Application
,	O
SPSS	B-Algorithm
,	O
and	O
SAS	B-Language
.	O
</s>
<s>
At	O
one	O
time	O
,	O
CMS	O
was	O
also	O
a	O
major	O
environment	O
for	O
e-mail	O
and	O
office	O
productivity	O
;	O
an	O
important	O
product	O
was	O
IBM	O
's	O
PROFS	B-Application
(	O
later	O
renamed	O
OfficeVision	B-Application
)	O
.	O
</s>
<s>
Two	O
commonly	O
used	O
CMS	O
tools	O
are	O
the	O
editor	O
XEDIT	B-Application
and	O
the	O
REXX	B-Language
programming	I-Language
language	I-Language
.	O
</s>
