SGI Indigo² and Challenge M
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The SGI Indigo² and the SGI Challenge M were Unix computers marketed by SGI from 1993 to 1997. The Indigo² was a desktop workstation. The Challenge M was a server which differed from the Indigo² only by a slightly differently colored and badged case, and the absence of graphics and sound hardware. Both systems were based on the MIPS processors.
Both systems supported EISA and GIO64 expansion buses via a riser card. Indigo² systems also supported SGI IMPACT graphics hardware. The IMPACT graphics boards draw more power than the GIO-64 bus can deliver, so the IMPACT-ready systems have additional power connectors on the expansion riser card, with a separate connection to the power supply. An IMPACT-ready Indigo² must have an IMPACT-ready riser card, an IMPACT-ready power supply, and a sufficiently recent PROM revision.
[edit] CPU
The Indigo² has three distinct variants, the 100-250MHz MIPS R4000 machines, the 75MHz MIPS R8000 machines, and the 175-195MHz R10000 machines.
All three variants had 12 SIMM slots on the motherboard, and could be expanded to a thermal spec maximum of either 384MB or 512MB RAM using industry standard 72-pin SIMMs. The design of the R10000 machines allowed for up to 1GB RAM in logic, but the thermal output of this older generation of DRAM chips necessitated the 512MB limit. With newer, higher-density and smaller scale modules, 768MB was easily within heat output specifications. Later, 128MB modules would allow the full 1GB with eight of twelve sockets occupied.
[edit] Graphics
The graphics boards available for the Indigo² were the pre-IMPACT boards (which included the SGI XL24, SGI XZ, SGI Elan and SGI Extreme) and the MGRAS IMPACT boards (the SGI Solid IMPACT, the SGI High IMPACT, the SGI High IMPACT AA, and the SGI Maximum IMPACT). The Indigo2's replacement, the SGI Octane, offered an upgraded bus but featured the same graphics options, albeit in repackaged form.
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