<s>
XIO	B-Architecture
is	O
a	O
packet-based	O
,	O
high-performance	O
computer	B-General_Concept
bus	I-General_Concept
employed	O
by	O
the	O
SGI	B-Application
Origin	I-Application
2000	I-Application
,	O
Octane	B-Device
,	O
Altix	B-Architecture
,	O
Fuel	B-Device
and	O
Tezro	B-Device
machines	O
.	O
</s>
<s>
The	O
XIO	B-Architecture
forms	O
a	O
bus	O
between	O
high-performance	O
system	O
devices	O
and	O
the	O
memory	B-General_Concept
controller	I-General_Concept
.	O
</s>
<s>
XIO	B-Architecture
is	O
usually	O
used	O
in	O
a	O
star	O
topology	O
,	O
using	O
a	O
router	B-Protocol
ASIC	O
called	O
Crossbow	O
(	O
Xbow	O
)	O
to	O
connect	O
up	O
to	O
eight	O
fully	O
symmetrical	O
devices	O
in	O
a	O
system	O
(	O
one	O
of	O
them	O
is	O
usually	O
the	O
memory	B-General_Concept
controller	I-General_Concept
/	O
CPU	B-General_Concept
bridge	O
,	O
called	O
HEART	O
in	O
Octane	B-Device
or	O
Hub	O
in	O
Origin	O
)	O
.	O
</s>
<s>
Other	O
devices	O
known	O
to	O
have	O
XIO	B-Architecture
interfaces	O
are	O
:	O
</s>
<s>
The	O
XIO	B-Architecture
employs	O
two	O
source-synchronous	O
channels	O
(	O
one	O
in	O
each	O
direction	O
)	O
,	O
each	O
8	O
or	O
16	O
bits	O
wide	O
.	O
</s>
<s>
Each	O
of	O
the	O
devices	O
can	O
utilize	O
the	O
full	O
bandwidth	O
,	O
as	O
the	O
XBow	O
router	B-Protocol
prevents	O
collisions	O
by	O
being	O
able	O
to	O
route	O
between	O
any	O
two	O
points	O
.	O
</s>
<s>
It	O
is	O
probable	O
that	O
XIO	B-Architecture
uses	O
STL	O
(	O
which	O
SGI	O
likes	O
to	O
call	O
SGI	O
transistor	O
logic	O
)	O
low-voltage	O
single-ended	O
I/O	O
standard	O
.	O
</s>
<s>
CrossTown	O
is	O
a	O
version	O
of	O
XIO	B-Architecture
utilizing	O
PECL	B-General_Concept
for	O
differential	O
I/O	O
standard	O
(	O
like	O
NUMAlink	B-Architecture
)	O
for	O
longer	O
connections	O
.	O
</s>
<s>
Higher-level	O
encapsulation	O
differs	O
from	O
NUMAlink	B-Architecture
(	O
like	O
used	O
to	O
connect	O
HUB	O
chips	O
in	O
Origin-series	O
machines	O
)	O
.	O
</s>
<s>
XIO	B-Architecture
uses	O
very	O
delicate	O
compression	O
connectors	O
,	O
which	O
should	O
be	O
handled	O
with	O
extreme	O
care	O
.	O
</s>
