<s>
The	O
Cray	B-Device
XT3	I-Device
is	O
a	O
distributed	O
memory	O
massively	B-Operating_System
parallel	I-Operating_System
MIMD	B-Operating_System
supercomputer	B-Architecture
designed	O
by	O
Cray	O
Inc	O
.	O
with	O
Sandia	O
National	O
Laboratories	O
under	O
the	O
codename	O
Red	B-Operating_System
Storm	I-Operating_System
.	O
</s>
<s>
The	O
XT3	O
derives	O
much	O
of	O
its	O
architecture	O
from	O
the	O
previous	O
Cray	B-Device
T3E	I-Device
system	O
,	O
and	O
also	O
from	O
the	O
Intel	B-Device
ASCI	I-Device
Red	I-Device
supercomputer	B-Architecture
.	O
</s>
<s>
The	O
XT3	O
consists	O
of	O
between	O
192	O
and	O
32,768	O
processing	O
elements	O
(	O
PEs	O
)	O
,	O
where	O
each	O
PE	O
comprises	O
a	O
2.4	O
or	O
2.6	O
GHz	O
AMD	B-General_Concept
Opteron	I-General_Concept
processor	O
with	O
up	O
to	O
two	B-Architecture
cores	I-Architecture
,	O
a	O
custom	O
"	O
SeaStar	O
"	O
communications	O
chip	O
,	O
and	O
between	O
1	O
and	O
8	O
GB	O
of	O
RAM	B-Architecture
.	O
</s>
<s>
The	O
PowerPC	O
440	O
based	O
SeaStar	O
device	O
provides	O
a	O
6.4	O
gigabyte	O
per	O
second	O
connection	O
to	O
the	O
processor	O
across	O
HyperTransport	B-Device
,	O
as	O
well	O
as	O
six	O
8-gigabyte	O
per	O
second	O
links	O
to	O
neighboring	O
PEs	O
.	O
</s>
<s>
The	O
XT3	O
runs	O
an	O
operating	B-General_Concept
system	I-General_Concept
called	O
UNICOS/lc	B-Operating_System
that	O
partitions	O
the	O
machine	O
into	O
three	O
sections	O
,	O
the	O
largest	O
comprising	O
the	O
Compute	O
nodes	O
,	O
and	O
two	O
smaller	O
sections	O
for	O
Service	O
nodes	O
and	O
IO	O
nodes	O
.	O
</s>
<s>
In	O
UNICOS/lc	B-Operating_System
1.x	O
,	O
the	O
Compute	O
PEs	O
run	O
a	O
Sandia	O
developed	O
microkernel	B-Operating_System
called	O
Catamount	O
,	O
which	O
is	O
descended	O
from	O
the	O
SUNMOS	O
OS	O
of	O
the	O
Intel	B-Device
Paragon	I-Device
;	O
in	O
UNICOS/lc	B-Operating_System
2.0	O
,	O
Catamount	O
was	O
replaced	O
by	O
a	O
specially	O
tuned	O
version	O
of	O
Linux	B-Application
called	O
Compute	B-Application
Node	I-Application
Linux	I-Application
(	O
CNL	O
)	O
.	O
</s>
<s>
Service	O
and	O
IO	O
PEs	O
run	O
the	O
full	O
version	O
of	O
SuSE	O
Linux	B-Application
and	O
are	O
used	O
for	O
interactive	O
logins	O
,	O
systems	O
management	O
,	O
application	O
compiling	O
and	O
job	O
launch	O
.	O
</s>
<s>
I/O	O
PEs	O
use	O
physically	O
distinct	O
hardware	O
,	O
in	O
that	O
the	O
node	O
boards	O
include	O
PCI-X	O
slots	O
for	O
connections	O
to	O
Ethernet	O
and	O
Fibre	B-Architecture
Channel	I-Architecture
networks	O
.	O
</s>
<s>
Though	O
the	O
performance	O
of	O
each	O
XT3	O
model	O
will	O
vary	O
with	O
the	O
speed	O
and	O
number	O
of	O
processors	O
installed	O
,	O
the	O
November	O
2007	O
Top500	B-Operating_System
results	O
for	O
the	O
Red	B-Operating_System
Storm	I-Operating_System
machine	O
,	O
the	O
largest	O
XT3	O
machine	O
installed	O
at	O
Sandia	O
,	O
measured	O
102.7	O
teraflops	O
on	O
the	O
Linpack	O
benchmark	O
,	O
placing	O
it	O
at	O
#6	O
on	O
the	O
list	O
.	O
</s>
<s>
After	O
upgrades	O
in	O
2008	O
to	O
install	O
some	O
XT4	B-Device
nodes	O
with	O
quad-core	B-Architecture
Opterons	B-General_Concept
,	O
Red	B-Operating_System
Storm	I-Operating_System
achieved	O
248	O
teraflops	O
to	O
place	O
at	O
#9	O
on	O
the	O
November	O
2008	O
Top500	B-Operating_System
.	O
</s>
<s>
The	O
architecture	O
was	O
superseded	O
in	O
2006	O
by	O
the	O
Cray	B-Device
XT4	I-Device
.	O
</s>
