<s>
The	O
term	O
Group	B-Operating_System
Communication	I-Operating_System
System	I-Operating_System
(	O
GCS	O
)	O
refers	O
to	O
a	O
software	B-Device
platform	I-Device
that	O
implements	O
some	O
form	O
of	O
group	O
communication	O
.	O
</s>
<s>
Examples	O
of	O
group	B-Operating_System
communication	I-Operating_System
systems	I-Operating_System
include	O
IS-IS	B-Protocol
,	O
Spread	B-General_Concept
Toolkit	I-General_Concept
,	O
Appia	B-Operating_System
framework	I-Operating_System
,	O
QuickSilver	B-Operating_System
,	O
and	O
IBM	O
's	O
group	O
services	O
component	O
.	O
</s>
<s>
Group	B-Operating_System
communication	I-Operating_System
systems	I-Operating_System
commonly	O
provide	O
specific	O
guarantees	O
about	O
the	O
total	O
ordering	O
of	O
messages	O
,	O
such	O
as	O
if	O
the	O
sender	O
of	O
a	O
message	O
receives	O
it	O
back	O
from	O
the	O
GCS	O
,	O
then	O
it	O
is	O
certain	O
that	O
it	O
has	O
been	O
delivered	O
to	O
all	O
other	O
nodes	O
in	O
the	O
system	O
.	O
</s>
<s>
This	O
property	O
is	O
useful	O
when	O
constructing	O
data	B-Architecture
replication	I-Architecture
systems	O
.	O
</s>
