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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 Geometry Engines (GEs).
The first Indigo, code-named "Hollywood", was introduced on 22 July 1991. It was based on the IP12 processor board, which contained 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) was based on the IP20 processor board, which had a removable processor module (PM1 or PM2) containing a 64-bit MIPS R4000 (100 MHz) or R4400 processor (100 MHz or 150 MHz) that implemented the MIPS-III instruction set. The IP20 used standard 72-pin SIMMs with parity, and had 12 SIMM slots for a total of 384 MB of RAM at maximum.
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 the 56000 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 SGI IRIS 4D/3x series, which shared 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 attached to the GIO bus.
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 up to 6.5.22.
- "Silicon Graphics Multi-Media IRIS Indigo At $8,000". (23 July 1991). Computer Business Review.