<s>
Program	B-Operating_System
Composition	I-Operating_System
Notation	I-Operating_System
(	O
PCN	O
)	O
is	O
a	O
specification	O
notation	O
for	O
building	O
up	O
larger	O
programs	O
from	O
smaller	O
modules	O
or	O
programs	O
(	O
usually	O
written	O
in	O
C	B-Language
or	O
Fortran	B-Application
)	O
.	O
</s>
<s>
Efficient	O
parallel	B-Operating_System
programming	I-Operating_System
is	O
at	O
the	O
heart	O
of	O
PCN	O
.	O
</s>
<s>
Larger	O
composed	O
programs	O
are	O
intended	O
to	O
execute	O
efficiently	O
on	O
single-processor	O
machines	O
,	O
multiprocessors	B-Operating_System
with	O
shared	O
memory	O
or	O
distributed	O
multicomputers	B-Operating_System
.	O
</s>
<s>
PCN	O
includes	O
the	O
language	O
for	O
specifying	O
concurrent	B-Operating_System
algorithms	O
and	O
interfaces	O
to	O
C	B-Language
and	O
Fortran	B-Application
.	O
</s>
<s>
PCN	O
is	O
appropriate	O
for	O
applications	O
benefiting	O
from	O
parallel	B-Operating_System
computing	I-Operating_System
such	O
as	O
fluid	O
dynamics	O
,	O
and	O
climate	B-Application
modelling	I-Application
.	O
</s>
