<s>
The	O
Indigo	O
,	O
introduced	O
as	O
the	O
IRIS	B-Device
Indigo	I-Device
,	O
is	O
a	O
line	O
of	O
workstation	B-Device
computers	I-Device
developed	O
and	O
manufactured	O
by	O
Silicon	O
Graphics	O
,	O
Inc	O
.	O
(	O
SGI	O
)	O
.	O
</s>
<s>
The	O
Indigo	O
is	O
considered	O
one	O
of	O
the	O
most	O
capable	O
graphics	O
workstations	B-Device
of	O
its	O
era	O
,	O
and	O
was	O
essentially	O
peerless	O
in	O
the	O
realm	O
of	O
hardware-accelerated	O
three-dimensional	O
graphics	O
rendering	O
.	O
</s>
<s>
For	O
use	O
as	O
a	O
graphics	O
workstation	B-Device
,	O
the	O
Indigo	O
was	O
equipped	O
with	O
a	O
two-dimensional	O
framebuffer	B-Algorithm
or	O
,	O
for	O
use	O
as	O
a	O
3D	O
graphics	O
workstation	B-Device
,	O
with	O
the	O
Elan	B-General_Concept
graphics	I-General_Concept
subsystem	O
including	O
one	O
to	O
four	O
Geometry	O
Engines	O
(	O
GEs	O
)	O
.	O
</s>
<s>
The	O
Indigo	O
was	O
superseded	O
generally	O
by	O
the	O
SGI	B-Application
Indigo2	I-Application
,	O
and	O
in	O
the	O
low-cost	O
market	O
segment	O
by	O
the	O
SGI	B-Operating_System
Indy	I-Operating_System
.	O
</s>
<s>
It	O
is	O
based	O
on	O
the	O
IP12	O
processor	O
board	O
,	O
which	O
contains	O
a	O
32-bit	O
MIPS	O
R3000A	B-Device
microprocessor	O
soldered	O
on	O
the	O
board	O
and	O
proprietary	O
memory	O
slots	O
supporting	O
up	O
to	O
96MB	O
of	O
RAM	O
.	O
</s>
<s>
The	O
later	O
version	O
(	O
code-named	O
Blackjack	O
)	O
is	O
based	O
on	O
the	O
IP20	O
processor	O
board	O
,	O
which	O
has	O
a	O
removable	O
processor	O
module	O
(	O
PM1	O
or	O
PM2	O
)	O
containing	O
a	O
64-bit	O
MIPS	B-General_Concept
R4000	I-General_Concept
(	O
100MHz	O
)	O
or	O
R4400	B-General_Concept
processor	O
(	O
100MHz	O
or	O
150MHz	O
)	O
that	O
implements	O
the	O
MIPS-III	O
instruction	O
set	O
.	O
</s>
<s>
A	O
Motorola	B-General_Concept
56000	I-General_Concept
DSP	O
is	O
used	O
for	O
Audio	O
IO	O
,	O
giving	O
it	O
4-channel	O
16-bit	O
audio	O
.	O
</s>
<s>
Ethernet	O
is	O
supported	O
on	O
board	O
by	O
the	O
SEEQ	O
80C03	O
chipset	O
coupled	O
with	O
the	O
HPC	O
(	O
High-performance	O
Peripheral	O
Controller	O
)	O
,	O
which	O
provides	O
the	O
DMA	B-General_Concept
engine	I-General_Concept
.	O
</s>
<s>
The	O
HPC	O
interfaces	O
primarily	O
between	O
the	O
GIO	B-Architecture
bus	O
and	O
the	O
Ethernet	O
,	O
SCSI	B-Architecture
(	O
WD33C93	O
chipset	O
)	O
and	O
the	O
56000	O
DSP	O
.	O
</s>
<s>
The	O
GIO	B-Architecture
bus	O
interface	O
is	O
implemented	O
by	O
the	O
PIC	O
(	O
Processor	O
Interface	O
Controller	O
)	O
on	O
IP12	O
and	O
MC	O
(	O
Memory	B-General_Concept
Controller	I-General_Concept
)	O
on	O
IP20	O
.	O
</s>
<s>
Much	O
of	O
the	O
hardware	O
design	O
can	O
be	O
traced	O
back	O
to	O
the	O
SGI	O
IRIS	O
4D/3x	O
series	O
,	O
which	O
shared	O
the	O
same	O
memory	B-General_Concept
controller	I-General_Concept
,	O
Ethernet	O
,	O
SCSI	B-Architecture
,	O
and	O
optionally	O
DSP	O
as	O
the	O
IP12	O
Indigo	O
.	O
</s>
<s>
The	O
4D/30	O
,	O
4D/35	O
and	O
Indigo	O
R3000	B-Device
are	O
all	O
considered	O
IP12	O
machines	O
and	O
run	O
the	O
same	O
IRIX	B-Operating_System
kernel	O
.	O
</s>
<s>
The	O
Indigo	O
R3000	B-Device
is	O
effectively	O
a	O
reduced	O
cost	O
4D/35	O
without	O
a	O
VME	O
bus	O
.	O
</s>
<s>
The	O
PIC	O
supports	O
a	O
VME	O
expansion	O
bus	O
(	O
used	O
on	O
the	O
4D/3x	O
series	O
)	O
and	O
GIO	B-Architecture
expansion	O
slots	O
(	O
used	O
on	O
the	O
Indigo	O
)	O
.	O
</s>
<s>
In	O
all	O
IP12	O
,	O
IP20	O
,	O
and	O
IP22/IP24	O
(	O
see	O
SGI	B-Application
Indigo2	I-Application
)	O
systems	O
the	O
HPC	O
attached	O
to	O
the	O
GIO	B-Architecture
bus	O
.	O
</s>
<s>
For	O
entry	O
graphics	O
,	O
the	O
8-bit	O
color	O
frame	B-Algorithm
buffer	I-Algorithm
comes	O
in	O
three	O
versions	O
.	O
</s>
<s>
One	O
version	O
uses	O
the	O
system	O
's	O
GIO	B-Architecture
expansion	O
bus	O
.	O
</s>
<s>
Another	O
uses	O
the	O
main	O
backplane	O
like	O
the	O
XS	O
,	O
XZ	O
,	O
and	O
Elan	B-General_Concept
graphics	I-General_Concept
options	O
.	O
</s>
<s>
The	O
Indigo	O
was	O
designed	O
to	O
run	O
IRIX	B-Operating_System
,	O
SGI	O
's	O
version	O
of	O
Unix	B-Application
.	O
</s>
<s>
The	O
Indigos	O
with	O
R3000	B-Device
processors	O
are	O
supported	O
up	O
to	O
IRIX	B-Operating_System
version	O
5.3	O
,	O
and	O
Indigo	O
equipped	O
with	O
an	O
R4000	B-General_Concept
or	O
R4400	B-General_Concept
processor	O
can	O
run	O
up	O
to	O
IRIX	B-Operating_System
6.5.22	O
.	O
</s>
<s>
Additionally	O
,	O
the	O
free	O
Unix-like	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
NetBSD	B-Device
has	O
support	O
for	O
both	O
the	O
IP12	O
and	O
IP20	O
Indigos	O
as	O
part	O
of	O
the	O
sgimips	O
port	O
.	O
</s>
