SGI Indigo
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The SGI Indigo, also known as the SGI IRIS Indigo, was a line of computer workstations manufactured by SGI beginning in 1990. The initial Indigo (codename Hollywood) was based on the IP12 processor board, which contained a 32-bit MIPS R3000A RISC processor soldered on the board and proprietary memory slots. The later version (codename Blackjack) was based on the IP20 processor board, which had a removable processor module (PM1 or PM2) containing a 64-bit MIPS R4000 or R4400 processor. The IP20 used standard 72-pin DIMMs with parity.
The Indigo was designed to run SGI's version of UNIX, known as IRIX. The Indigos with R3000 processors were supported in IRIX through version 5.3 of that operating system, while Indigos equipped with an R4000 or R4400 processor can run IRIX 6.5. Additionally, the free Unix-like operating system NetBSD has support for both the IP12 and IP20 Indigos as part of the sgimips port.
The Indigo was 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 GEs (Geometry Engines).
A Motorola 56000 DSP was used for Audio IO. 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 m56000 DSP. The GIO bus interface is implemented by the PIC (Processor Interface Controller) on IP12 and MC (Memory Controller) on IP20. Much of the hardware design can be traced back to the 4D/3x series, which shares the same memory controller, Ethernet, SCSI, and optionally DSP as the IP12 Indigo. Indeed, the 4D/30, 4D/35 and Indigo R3000 are all considered IP12 machines and run the same IRIX kernel. The Indigo R3000 is effectively a reduced cost 4D/35 without a VME bus. The PIC supports a VME expansion bus (used on the 4D/3x series) and GIO expansion slots (used on the Indigo). In all IP12, IP20, and IP22/IP24 (see SGI Indigo2) systems the HPC attaches to the GIO bus.
The Indigo was a visually pleasing design, based on a simple cube motif in indigo hue. Graphics and other peripheral expansions were 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), although Indigos remain useful among some specialties even into the 2000s.
