<s>
The	O
Cray	B-Device
XT4	I-Device
(	O
codenamed	O
Hood	O
during	O
development	O
)	O
is	O
an	O
updated	O
version	O
of	O
the	O
Cray	B-Device
XT3	I-Device
supercomputer	B-Architecture
.	O
</s>
<s>
It	O
includes	O
an	O
updated	O
version	O
of	O
the	O
SeaStar	O
interconnect	O
router	O
called	O
SeaStar2	O
,	O
processor	O
sockets	O
for	O
Socket	O
AM2	O
Opteron	B-General_Concept
processors	O
,	O
and	O
240-pin	O
unbuffered	O
DDR2	O
memory	O
.	O
</s>
<s>
The	O
XT4	B-Device
also	O
includes	O
support	O
for	O
FPGA	B-Architecture
coprocessors	O
that	O
plug	O
into	O
riser	O
cards	O
in	O
the	O
Service	O
and	O
IO	O
blades	O
.	O
</s>
<s>
The	O
interconnect	O
,	O
cabinet	O
,	O
system	O
software	O
and	O
programming	O
environment	O
remain	O
unchanged	O
from	O
the	O
Cray	B-Device
XT3	I-Device
.	O
</s>
<s>
It	O
was	O
superseded	O
in	O
2007	O
by	O
the	O
Cray	B-Device
XT5	I-Device
.	O
</s>
