SGI Indigo

The Indigo, introduced as the IRIS Indigo, is a line of workstation computers developed and manufactured by Silicon Graphics, Inc. (SGI). SGI first announced the system in July 1991.

The Indigo is considered one of the most capable graphics workstations of its era, and was essentially peerless in the realm of hardware-accelerated three-dimensional graphics rendering. For use as a graphics workstation, the Indigo was equipped with a two-dimensional framebuffer or, for use as a 3D graphics workstation, with the Elan graphics subsystem including one to four Geometry Engines (GEs). SGI sold a server version with no video adapter.

The Indigo's design is based on a simple cube motif in indigo hue. Graphics and other peripheral expansions are accomplished via the GIO32 expansion bus.

The Indigo was superseded generally by the SGI Indigo2, and in the low-cost market segment by the SGI Indy.

The first Indigo model, code-named "Hollywood", was introduced on July 22, 1991. It is based on the IP12 processor board, which contains a 32-bit MIPS R3000A microprocessor soldered on the board and proprietary memory slots supporting up to 96 MB of RAM.

The later version (codename Blackjack) is based on the IP20 processor board, which has a removable processor module (PM1 or PM2) containing a 64-bit MIPS R4000 (100 MHz) or R4400 processor (100 MHz or 150 MHz) that implements the MIPS-III instruction set. The IP20 uses standard 72-pin SIMMs with parity, and has 12 SIMM slots for a total of 384 MB of RAM at maximum.

A Motorola 56000 DSP is used for Audio IO, giving it 4 channel 16-bit audio. Ethernet is supported onboard by the SEEQ 80c03 chipset coupled with the HPC (High-performance Peripheral Controller), which provides the DMA engine. The HPC interfaces primarily between the GIObus and the Ethernet, SCSI (wd33c93 chipset) and the 56000 DSP. The GIO bus interface is implemented by the PIC (Processor Interface Controller) on IP12 and MC (Memory Controller) on IP20.

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