<s>
The	O
O2	O
was	O
an	O
entry-level	O
Unix	B-Device
workstation	I-Device
introduced	O
in	O
1996	O
by	O
Silicon	O
Graphics	O
,	O
Inc	O
.	O
(	O
SGI	O
)	O
to	O
replace	O
their	O
earlier	O
Indy	B-Operating_System
series	O
.	O
</s>
<s>
Like	O
the	O
Indy	B-Operating_System
,	O
the	O
O2	O
used	O
a	O
single	O
MIPS	B-Device
microprocessor	B-Architecture
and	O
was	O
intended	O
to	O
be	O
used	O
mainly	O
for	O
multimedia	O
.	O
</s>
<s>
Its	O
larger	O
counterpart	O
was	O
the	O
SGI	B-Device
Octane	I-Device
.	O
</s>
<s>
The	O
O2	O
was	O
SGI	O
's	O
last	O
attempt	O
at	O
a	O
low-end	O
workstation	B-Device
.	O
</s>
<s>
Originally	O
known	O
as	O
the	O
"	O
Moosehead	O
"	O
project	O
,	O
the	O
O2	O
architecture	B-General_Concept
featured	O
a	O
proprietary	O
high-bandwidth	O
Unified	O
Memory	O
Architecture	B-General_Concept
(	O
UMA	O
)	O
to	O
connect	O
system	O
components	O
.	O
</s>
<s>
A	O
PCI	B-Protocol
bus	I-Protocol
is	O
bridged	O
onto	O
the	O
UMA	O
with	O
one	O
slot	O
available	O
.	O
</s>
<s>
Two	O
SCSI	O
drives	O
could	O
be	O
mounted	O
on	O
special	O
caddies	O
(	O
1	O
in	O
the	O
later	O
R10000/R12000	O
models	O
due	O
to	O
heat	O
constraints	O
)	O
and	O
an	O
optional	O
video	O
capture	O
/	O
sound	O
cassette	O
mounted	O
on	O
the	O
far	O
left	O
side	O
.	O
</s>
<s>
The	O
O2	O
comes	O
in	O
two	O
distinct	O
CPU	O
flavours	O
;	O
the	O
low-end	O
MIPS	B-Device
180	O
to	O
350MHz	O
R5000	B-General_Concept
-	O
or	O
RM7000-based	O
units	O
and	O
the	O
higher-end	O
150	O
to	O
400MHz	O
R10000	B-General_Concept
-	O
or	O
R12000-based	O
units	O
.	O
</s>
<s>
The	O
200MHz	O
R5000	B-General_Concept
CPUs	O
with	O
1	O
MB	O
L2-cache	O
are	O
generally	O
noticeably	O
faster	O
than	O
the	O
180MHz	O
R5000s	B-General_Concept
with	O
512	O
KB	O
cache	O
.	O
</s>
<s>
There	O
is	O
a	O
hobbyist	O
that	O
has	O
successfully	O
retrofitted	O
a	O
600MHz	O
RM7xxx	O
MIPS	B-Device
processor	O
into	O
the	O
O2	O
.	O
</s>
<s>
There	O
are	O
eight	O
DIMM	B-General_Concept
slots	O
on	O
the	O
motherboard	O
and	O
memory	O
,	O
and	O
all	O
O2s	O
are	O
expandable	O
to	O
1	O
GB	O
using	O
proprietary	O
239-pin	O
SDRAM	O
DIMMs	B-General_Concept
.	O
</s>
<s>
The	O
Memory	O
&	O
Rendering	O
Engine	O
(	O
MRE	O
)	O
ASIC	O
contains	O
the	O
memory	B-General_Concept
controller	I-General_Concept
.	O
</s>
<s>
Memory	O
is	O
accessed	O
via	O
a	O
133MHz	O
144-bit	O
bus	O
,	O
of	O
which	O
128	O
bits	O
are	O
for	O
data	O
and	O
the	O
remaining	O
for	O
ECC	B-General_Concept
.	O
</s>
<s>
The	O
ASIC	O
provides	O
a	O
64-bit	O
PCI	B-Protocol
bus	I-Protocol
,	O
an	O
ISA	B-Architecture
bus	I-Architecture
,	O
two	O
PS/2	B-Protocol
ports	I-Protocol
for	O
keyboard	O
and	O
mouse	O
,	O
and	O
a	O
10/100	O
Base-T	O
Ethernet	O
port	O
.	O
</s>
<s>
The	O
PCI	B-Protocol
bus	I-Protocol
has	O
one	O
64-bit	O
slot	O
,	O
but	O
the	O
ISA	B-Architecture
bus	I-Architecture
is	O
present	O
solely	O
for	O
attaching	O
a	O
Super	B-Device
I/O	I-Device
chip	O
to	O
provide	O
serial	O
and	O
parallel	O
ports	O
.	O
</s>
<s>
Older	O
O2	O
's	O
generally	O
have	O
4x	O
speed	O
Toshiba	O
CD-ROMs	O
,	O
but	O
any	O
Toshiba	O
SCSI	O
CD-ROM	O
can	O
be	O
used	O
(	O
as	O
well	O
as	O
from	O
other	O
manufacturers	O
,	O
the	O
bezel	O
replacement	O
however	O
is	O
designed	O
to	O
fit	O
Toshiba	O
design	O
and	O
also	O
IRIX	B-Operating_System
cannot	O
utilize	O
CD-DA	O
mode	O
other	O
than	O
Toshiba	O
)	O
.	O
</s>
<s>
The	O
R5000/RM7000	O
units	O
have	O
two	O
available	O
drive	O
sleds	O
for	O
SCA	O
UltraWide	O
SCSI	O
hard-disks	O
.	O
</s>
<s>
Because	O
the	O
R10000/R12000	O
CPU	O
module	O
has	O
a	O
much	O
higher	O
cooling-fan	O
assembly	O
,	O
the	O
R10000/R12000	O
units	O
have	O
room	O
for	O
only	O
one	O
drive-sled	O
.	O
</s>
<s>
It	O
was	O
developed	O
to	O
be	O
a	O
low-cost	O
implementation	O
of	O
the	O
OpenGL	B-Application
1.1	O
architecture	B-General_Concept
with	O
ARB	O
image	O
extensions	O
in	O
both	O
software	O
and	O
hardware	O
.	O
</s>
<s>
The	O
chipset	O
consists	O
of	O
the	O
microprocessor	B-Architecture
,	O
and	O
the	O
ICE	O
,	O
MRE	O
and	O
Display	O
ASICs	O
.	O
</s>
<s>
All	O
display	O
list	O
and	O
vertex	O
processing	O
,	O
as	O
well	O
as	O
the	O
control	O
of	O
the	O
MRE	O
ASIC	O
is	O
performed	O
by	O
the	O
microprocessor	B-Architecture
.	O
</s>
<s>
Due	O
to	O
the	O
unified	O
memory	O
architecture	B-General_Concept
,	O
the	O
texture	O
and	O
framebuffer	O
memory	O
comes	O
from	O
main	O
memory	O
,	O
resulting	O
in	O
a	O
system	O
that	O
has	O
a	O
variable	O
amount	O
of	O
each	O
memory	O
.	O
</s>
<s>
Several	O
operating	B-General_Concept
systems	I-General_Concept
support	O
the	O
O2	O
:	O
</s>
<s>
IRIX	B-Operating_System
6.3	O
or	O
6.5.x	O
(	O
native	O
platform	O
)	O
.	O
</s>
<s>
Linux	B-Application
port	O
is	O
working	O
,	O
but	O
some	O
drivers	O
are	O
missing	O
.	O
</s>
<s>
Both	O
Gentoo	B-Application
and	O
Debian	O
have	O
releases	O
that	O
work	O
on	O
the	O
O2	O
.	O
</s>
<s>
See	O
the	O
page	O
on	O
linux-mips.org	O
.	O
</s>
<s>
OpenBSD	B-Operating_System
ran	O
on	O
the	O
O2	O
starting	O
from	O
OpenBSD	B-Operating_System
3.7	O
until	O
the	O
discontinuation	O
of	O
the	O
"	O
sgi	O
"	O
port	O
in	O
OpenBSD	B-Operating_System
6.9	O
.	O
</s>
<s>
NetBSD	B-Device
has	O
run	O
on	O
the	O
O2	O
since	O
NetBSD	B-Device
2.0	O
.	O
</s>
<s>
It	O
was	O
the	O
first	O
Open	B-License
Source	I-License
operating	B-General_Concept
system	I-General_Concept
to	O
be	O
ported	O
to	O
the	O
O2	O
.	O
</s>
<s>
The	O
SGI	B-Device
O2	I-Device
has	O
an	O
Imaging	O
and	O
Compression	O
Engine	O
(	O
ICE	O
)	O
application-specific	O
integrated	O
circuit	O
(	O
ASIC	O
)	O
for	O
processing	O
streaming	O
media	O
and	O
still	O
images	O
.	O
</s>
<s>
ICE	O
operates	O
at	O
66MHz	O
and	O
contains	O
a	O
R3000-derived	O
microprocessor	B-Architecture
serving	O
as	O
the	O
scalar	O
unit	O
to	O
which	O
a	O
128-bit	O
SIMD	B-Device
unit	O
is	O
attached	O
using	O
the	O
MIPS	B-Device
coprocessor	O
interface	O
.	O
</s>
<s>
ICE	O
operates	O
on	O
eight	O
16-bit	O
or	O
sixteen	O
8-bit	O
integers	O
,	O
but	O
still	O
provides	O
a	O
significant	O
amount	O
of	O
computational	O
power	O
which	O
enables	O
the	O
O2	O
to	O
do	O
video	O
decoding	O
and	O
audio	O
tasks	O
that	O
would	O
require	O
a	O
much	O
faster	O
CPU	O
if	O
done	O
without	O
SIMD	B-Device
instructions	O
.	O
</s>
<s>
ICE	O
only	O
works	O
with	O
the	O
IRIX	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
,	O
as	O
this	O
is	O
the	O
only	O
system	O
that	O
has	O
drivers	O
capable	O
of	O
taking	O
advantage	O
of	O
this	O
device	O
.	O
</s>
<s>
The	O
Unified	O
Memory	O
Architecture	B-General_Concept
means	O
that	O
the	O
O2	O
uses	O
main	O
memory	O
for	O
graphics	O
textures	O
,	O
making	O
texturing	O
polygons	O
and	O
other	O
graphics	O
elements	O
trivial	O
.	O
</s>
<s>
The	O
O2	O
's	O
graphics	O
is	O
known	O
to	O
have	O
slower	O
rasterization	O
speed	O
than	O
the	O
Indigo2	B-Application
's	O
Maximum	O
IMPACT	O
graphics	O
boards	O
,	O
though	O
the	O
Maximum	O
IMPACT	O
graphics	O
is	O
limited	O
to	O
4	O
MB	O
of	O
texture	O
memory	O
,	O
which	O
can	O
result	O
in	O
thrashing	O
,	O
whereas	O
the	O
O2	O
is	O
limited	O
only	O
by	O
available	O
memory	O
.	O
</s>
<s>
Intel	O
's	O
Pentium	B-General_Concept
and	O
AMD	O
's	O
K5	O
)	O
.	O
</s>
