<s>
MPICH	B-Library
,	O
formerly	O
known	O
as	O
MPICH2	B-Library
,	O
is	O
a	O
freely	O
available	O
,	O
portable	O
implementation	O
of	O
MPI	B-Application
,	O
a	O
standard	O
for	O
message-passing	O
for	O
distributed-memory	O
applications	O
used	O
in	O
parallel	B-Operating_System
computing	I-Operating_System
.	O
</s>
<s>
MPICH	B-Library
is	O
Free	B-Application
and	I-Application
open	I-Application
source	I-Application
software	I-Application
with	O
some	O
public	B-Application
domain	I-Application
components	O
that	O
were	O
developed	O
by	O
a	O
US	O
governmental	O
organisation	O
,	O
and	O
is	O
available	O
for	O
most	O
flavours	O
of	O
Unix-like	B-Operating_System
OS	I-Operating_System
(	O
including	O
Linux	B-Application
and	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
)	O
.	O
</s>
<s>
The	O
Argonne	O
National	O
Laboratory	O
and	O
Mississippi	O
State	O
University	O
jointly	O
developed	O
early	O
versions	O
(	O
MPICH-1	O
)	O
as	O
public	B-Application
domain	I-Application
software	I-Application
.	O
</s>
<s>
The	O
CH	O
part	O
of	O
the	O
name	O
was	O
derived	O
from	O
"	O
Chameleon	O
"	O
,	O
which	O
was	O
a	O
portable	O
parallel	B-Operating_System
programming	I-Operating_System
library	O
developed	O
by	O
William	O
Gropp	O
,	O
one	O
of	O
the	O
founders	O
of	O
MPICH	B-Library
.	O
</s>
<s>
The	O
original	O
implementation	O
of	O
MPICH	B-Library
(	O
sometimes	O
called	O
"	O
MPICH1	O
"	O
)	O
implemented	O
the	O
MPI-1.1	O
standard	O
.	O
</s>
<s>
Starting	O
around	O
2001	O
,	O
work	O
began	O
on	O
a	O
new	O
code	O
base	O
to	O
replace	O
the	O
MPICH1	O
code	O
and	O
support	O
the	O
MPI-2	O
standard	O
.	O
</s>
<s>
Until	O
November	O
2012	O
,	O
this	O
project	O
was	O
known	O
as	O
"	O
MPICH2	B-Library
"	O
.	O
</s>
<s>
As	O
of	O
November	O
2012	O
,	O
the	O
MPICH2	B-Library
project	O
renamed	O
itself	O
to	O
simply	O
"	O
MPICH	B-Library
"	O
.	O
</s>
<s>
MPICH	B-Library
v3.0	O
implements	O
the	O
MPI-3.0	O
standard	O
.	O
</s>
<s>
MPICH	B-Library
v4.0	O
implements	O
the	O
MPI-4.0	O
standard	O
.	O
</s>
<s>
MPICH	B-Library
is	O
one	O
of	O
the	O
most	O
popular	O
implementations	O
of	O
MPI	B-Application
.	O
</s>
<s>
It	O
is	O
used	O
as	O
the	O
foundation	O
for	O
the	O
vast	O
majority	O
of	O
MPI	B-Application
implementations	O
,	O
including	O
IBM	O
MPI	B-Application
(	O
for	O
Blue	B-Operating_System
Gene	I-Operating_System
)	O
,	O
Intel	O
MPI	B-Application
,	O
Cray	O
MPI	B-Application
,	O
Microsoft	O
MPI	B-Application
,	O
Myricom	O
MPI	B-Application
,	O
OSU	O
MVAPICH/MVAPICH2	O
,	O
and	O
many	O
others	O
.	O
</s>
