SGI Indigo² and Challenge M

Microprocessor

All Indigo2 models use one of four distinct MIPS microprocessor variants: the 100 to 250 MHz MIPS R4000 and R4400, and the Quantum Effect Devices R4600 (IP22 mainboard); the 75 MHz MIPS R8000 (IP26 mainboard); and the 175 to 195 MHz R10000 (IP28 mainboard), which are featured in the last produced Indigo² model, the "IMPACT10000". Each microprocessor family differs in clock frequency, primary and secondary cache capacity.

RAM

All SGI Indigo2 models have 12 SIMM slots on the motherboard. The Indigo2 uses standard 36-bit parity 72-pin fast page mode SIMM memory. The memory modules are seated in groups of four. Indigo² could be expanded to a thermal specification maximum of either 384 MB or 512 MB RAM. The design of the memory control logic in R10000 machines support up to 1 GB RAM, but the thermal output of older generation of DRAM chips necessitate the 512 MB limit. With newer, higher-density and smaller scale modules, 768 MB is easily within heat output specifications. Later, 128 MB modules allow the full 1 GB with eight out of twelve sockets occupied.

Storage

All Indigo2 models can accommodate two 3.5" sized SCSI disk drives and one 5.25" sized SCSI CD-ROM drive inside bays on the front of the machine, using specially designed Indigo2 drive sleds with proprietary connectors. All of three drive bays are easily accessed when removing the stylish and recognizable Indigo2 front bezel. The internal SCSI bus speed of the Indigo2 is about 10 megabytes per second. The usual hard disk devices used by the manufacturer are narrow or SCSI-1 5200rpm and 7200rpm drives. All of the Indigo2 drive sleds have classic 50 pin female SCSI-1 connector + standard 4 pin power connector. Advanced U160 and U320 SCSI disk drives can also be used but then one needs appropriate adapters (80/68pin to 50pin SCSI).

Networking

10Mb on-board LAN interface, 100Mb LAN options were made by third parties, either via EISA or GIO64 expansion cards. The two most known and widely used Indigo2 network cards are 3Com 3C597-TX 100Mbit EISA Card, and the Phobos G160 GIO64. The second one offers better overall performance due to using the superior GIO64 bus, which also has the effect of reducing the CPU utilization due to DMA transfers.

Graphics

The graphics options available for the Indigo2 can be divided in two groups: the "pre-IMPACT" and the "MGRAS IMPACT" boards.

"Pre-IMPACT" options consist of the following options: SGI XL24, SGI XZ, SGI Elan and SGI Extreme). These options are based on the same "Express Graphics" architecture from the original SGI Indigo, but feature improved performance.

The MGRAS IMPACT (or just "IMPACT") family include the Solid IMPACT, High IMPACT, High IMPACT AA, and the Maximum IMPACT. These newer boards have a different architecture than the earlier designs. Physically, they appear to be similar to the older graphics options; the low-end Solid IMPACT board takes up a single GIO-64 slot, the mid-range High IMPACT takes up two GIO-64 slots, and the high end Maximum IMPACT takes occupies three. The High IMPACT and Solid IMPACT boards provides the same performance for non-textured tasks, while the Maximum IMPACT provides double the performance. The High IMPACT AA option has the geometry performance of a Maximum IMPACT, but is otherwise the same as the High IMPACT including the pixel fill performance.

The IMPACT graphics is the first desktop graphics system from SGI to offer texture mapping acceleration, though only the High IMPACT and Maximum IMPACT had this capability, and comes with 1 MB of texture memory as standard. The Solid IMPACT card is named "Solid" due to its applications for solid (non-textured) modeling. When expanded by adding a TRAM (Texture RAM) module to the board, the amount of texture memory can be increased to 4 MB. Maximum IMPACT graphics require two of these modules due its two pixel units, although this does not upgrade them to 8 MB, with the two modules merely working in parallel to render twice as fast. At the time of its release, Maximum IMPACT graphics was the world's fastest available top-end desktop visualization solution. A Maximum IMPACT with 4 MB of texture memory and the correct graphics settings can play id Software's Quake 1, 2 or 3 with acceptable frame rates.

All graphics options for Indigo2 uses the standard 13W3 connector for connecting the monitor and another connector for 3D stereoscopic glasses.

It is possible to have a dual-head Indigo2 by merely adding another Solid IMPACT card. Valid configurations include Solid/Solid, Solid/High, Solid/Maximum. Although there are four GIO-64 slots available and the High IMPACT takes up two, it is not possible to have a High/High configuration.

The IMPACT boards draw more power than the GIO-64 bus can deliver, so 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. The Indigo2's replacement, the SGI Octane, offers an upgraded XIO bus but features the same graphics options, albeit in repackaged form.