<s>
Group	B-Application
Control	I-Application
System	I-Application
(	O
GCS	O
)	O
is	O
an	O
operating	B-General_Concept
system	I-General_Concept
made	O
by	O
IBM	O
,	O
meant	O
to	O
run	O
as	O
a	O
guest	O
of	O
VM	B-Application
.	O
</s>
<s>
GCS	O
is	O
an	O
integral	O
component	O
of	O
the	O
discontinued	O
VM/SP	B-Application
(	O
since	O
VM/SP	B-Application
4	O
)	O
,	O
VM/XA	O
SP	O
,	O
VM/ESA	B-Application
and	O
current	O
z/VM	B-Application
IBM	O
System	O
product	O
offerings	O
.	O
</s>
<s>
GCS	O
's	O
purpose	O
is	O
to	O
provide	O
an	O
environment	O
to	O
run	O
some	O
specific	O
OS/MVS	B-Application
-based	O
applications	O
and	O
networking	O
middleware	B-General_Concept
under	O
VM	B-Application
.	O
</s>
<s>
To	O
this	O
end	O
,	O
GCS	O
provides	O
a	O
limited	O
simulation	O
of	O
the	O
OS/MVS	B-Application
APIs	O
.	O
</s>
<s>
While	O
CMS	B-Operating_System
,	O
the	O
usual	O
VM	B-Application
guest	O
,	O
already	O
has	O
OS	O
simulation	O
,	O
it	O
is	O
not	O
extensive	O
enough	O
to	O
run	O
some	O
applications	O
such	O
as	O
VTAM	B-Application
.	O
</s>
<s>
Specifically	O
,	O
GCS	O
provides	O
OS	B-Operating_System
multitasking	I-Operating_System
support	O
.	O
</s>
<s>
GCS	O
is	O
not	O
designed	O
to	O
be	O
a	O
multi-purpose	O
user	O
operating	B-General_Concept
system	I-General_Concept
such	O
as	O
CMS	B-Operating_System
.	O
</s>
