<s>
Global	B-Application
Resource	I-Application
Serialization	I-Application
(	O
GRS	O
)	O
is	O
the	O
component	O
within	O
the	O
IBM	B-Application
z/OS	I-Application
operating	O
system	O
responsible	O
for	O
enabling	O
fair	O
access	O
to	O
serially	O
reusable	O
computing	O
resources	O
,	O
such	O
as	O
datasets	O
and	O
tape	O
drives	O
or	O
virtual	O
resources	O
,	O
such	O
as	O
lists	O
,	O
queues	O
,	O
and	O
control	O
blocks	O
.	O
</s>
<s>
STEP	O
-	O
this	O
level	O
is	O
for	O
resources	O
that	O
exist	O
within	O
a	O
single	O
MVS	B-Application
address	O
space	O
.	O
</s>
<s>
SYSTEM	O
-	O
this	O
level	O
is	O
for	O
resources	O
that	O
exist	O
within	O
a	O
single	O
MVS	B-Application
instance	O
.	O
</s>
<s>
SYSTEMS	O
-	O
also	O
known	O
as	O
GLOBAL	O
,	O
these	O
resources	O
are	O
accessible	O
by	O
multiple	O
MVS	B-Application
instances	O
.	O
</s>
<s>
GRS	O
Ring	O
-	O
each	O
of	O
the	O
systems	O
(	O
LPARs	B-Device
)	O
are	O
connected	O
with	O
channel-to-channel	O
adapters	O
(	O
CTCAs	O
)	O
in	O
a	O
ring	O
configuration	O
.	O
</s>
<s>
GRS	O
Star	O
(	O
Parallel	B-Operating_System
Sysplex	I-Operating_System
)	O
-	O
Rather	O
than	O
using	O
a	O
message	O
passing	O
protocol	O
to	O
manage	O
resource	O
ownership	O
succession	O
,	O
GRS	O
uses	O
the	O
locking	O
services	O
provided	O
by	O
the	O
XES	O
(	O
Cross	O
System	O
Extended	O
Services	O
)	O
component	O
of	O
MVS	B-Application
.	O
</s>
