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Silicon Graphics Indigo2

Personal Computer World, May 1993

(Historical Article)

[SGI Indigo2] If a computer could be the stuff of dreams, the Indigo2 is it. Nick Edmunds, treated to an exclusive review, had two days to drool over its stunning graphics, unsurpassed MIPS-based speed and distinctive good looks.

[Right: The Indigo2. Click to download a larger 655x626 version]

The brand new Indigo2, the latest machine from Silicon Graphics, is not your average desktop PC; it is the stuff of dreams. Its turquoise case, crammed with leading edge technology, will set you back a mere 34,000 UKP.

Silicon Graphics (SGI) flew the Indigo2 into the country and gave it to PCW for a European exclusive review. Two days later it was back on another plane and flying home to SGI's Mountain View headquarters in California. While it was winging its way back across the Atlantic, the PCW office was still abuzz. Talk was of the incredible moving 3D imaging, the size of the graphics 'card', the memory, the sound, and of course the cost. For that money you could buy a lot of other hardware, but the decision was unanimous. Thirty-four cheapo 486 PCs or an Indigo2? An Indigo2, please.

Silicon Graphics started life in 1982 to concentrate on 3D graphics. Business has boomed and 1991 saw annual revenues of $900 million and around 3500 staff. The company doesn't make IBM compatible PCs; it sticks to workstations and then only in colour. This newest member of its Indigo family of desktops is by far the fastest. SGI makes bigger machines in its Challenge series, but these need the strength and space of the floor to sit on.

Graphics is about making data understandable. A spreadsheet will give you a row of numbers which, although detailed, hides the overall picture of directions or patterns. If you graph the same data in a pie chart or bar graph, proportions, trends and anomalies will immediately leap out at you from the screen. The fact that simple spreadsheet results can benefit from visualisation illustrates the gains available when dealing with more complex data. Oil companies want to interpret seismic oil exploration data, aircraft manufacturers look at airflow over a wing tip and architects design buildings on computer.

Using the CPU and displaying the results using the graphics system are two separate processes, and for a desktop machine the Indigo2 packs a punch in both areas. Its CPU is the ultra-quick (by PC standards) MIPS 100MHz R4000 RISC chip. Its graphics hardware, the Extreme Graphics subsystem, is so stuffed with interconnected processors that it has to be seen to be believed.

The Indigo2 is designed for the MIPS R4000 and the faster R4400 chip. MIPS came to fame with the publicity surrounding the ACE (Advanced Computing Environment) initiative. Now defunct, ACE was a consortium of hardware and software vendors who wanted a processor and operating system platform independent of any one supplier a good idea after years of being dictated to by IBM or Intel. The R4000 was chosen as one of its processors along with a version of Unix and Microsoft's NT (the R4000 will run either). With ACE faltering, MIPS was taken over by Silicon Graphics and is now a wholly owned subsidiary. It continues to design and supply chips for other manufacturers and the R4000 is made under licence by a number of companies including NEC, Siemens and LSI Logic.

The R4000 comes from a family of RISC chips, the other members being the R2000, R3000 and R6000. The R4000 group are the fastest and only 64-bit processors. The three models, the R4000PC, R4000SC and R4000MC all run at 100MHz internally on a 50MHz daughterboard. The R4000PC is packaged in a 179 PGA (Pin Grid Array - the normal grey ceramic square with gold pins) and is designed for low-cost desktops. The R4000SC has more performance with 447 pins and secondary cache, while the R4000MC is another 447-pin secondary cache chip designed for multiprocessing machines. The SC and MC models are about 50% faster than the PC.

The latest MIPS chip, the 4400, is expected to ship in the summer quarter. It comes in the same versions as the R4000 and is pin compatible. All three versions have 32K of on-chip cache (double that of the R4000) and the SC and MC versions are designed to cope with a huge, 4MB external secondary cache. The R4400 comes in three clock speeds and will run (doubled, like the R4000) internally at 100, 134 and 150MHz. Both 5v and 3.3v versions will be available, the latter destined for use in low power PCs such as notebooks. The 150MHz R4400 will certainly be fast if it lives up to its claim of being 'the first processor designed for the PC to run at over 100 SPECMarks'. Against other RISC processors the R4400 looks good: MIPS claims it has faster integer and task swapping performance than DEC'S new and exciting Alpha chip. But the Alpha has faster floating point performance (even MIPS won't deny this) and this is crucial for most scientific applications which deal in real arithmetic. The adoption of the Alpha by Cray Research for use in some of its machines speaks volumes for its ability in this area. Most PC DOS/Windows applications in use today, however, hardly use the floating point capabilities found in the co-processor (built into chips like the 486). Exceptions would be packages like AutoCAD and the calculations in some GUI scalable fonts.

MIPS believes it can manufacture the R4400 more cheaply than other competing processors, and the arrival of Intel's long heralded Pentium chip and the even more tardy NT 32-bit operating system from Microsoft should prove interesting. The top end of the PC market, where NT is aimed, will be up for grabs as NT will run as happily on a R4000 as anything else. At last, then, the PC processor choice will not be Intel or Intel.

Further MIPS chips on the drawing board are a 200MHz version of the R4400, and later, maybe in 1994, an entirely new chip running at 250MHz. Other projects include a chip designed specifically for floating point work and a cheap ($50) 486 basher, samples of which may appear this year.

And so to Silicon Graphics' deliciously hi-tech Indigo2. Its turquoise colour stands out from the usual corporate mushroom grey identi-boxes, while at 19in square and 5in high it is smaller than many 'ordinary' and infinitely less powerful desktop PCs on sale today. The 'cooling fins' ribbed styling extends all the way round the case.

A section of the front panel hinges down to reveal the power switch and an empty 5.25in half height drive bay for use typically with a CD-ROM. Alongside this is a DAT (Digital Audio Tape) drive. There isn't a 3.5in floppy drive in sight although one is available if you insist. The DAT has a maximum capacity of 2GB, uses 4mm tape and is [oh dear, I seem to be missing 2 pages; I'll insert them when I can find them].

[Extreme Graphics Board Set]
The Extreme Graphics subsystem can deliver 1024 x 1280 pixels in 24bits at blinding speeds. The price? A mere 8000 UKP.

  1. Command Engine - The HQ2 is an 80,000 gate device that delegates graphics primitives to the Geometry Engine processors.

  2. Eight Geometry Engines - Provide 256MFlops through an effective multi-chip module design.

  3. Dual Integrated Raster Engines - Two RE3 Raster Engines hold 200,000 custom gates running at 50MHz.

  4. Live Video I/O Slot - A port for video expansion using Indigo2 Video and Galileo Video options.

In the present configuration, all but one of the EISA sockets are obscured by the massive Extreme Graphics subsystem. This full length, three card block of chips is in fact the heart of the machine. The Extreme Graphics subsystem itself, which costs about 8000 UKP, has chips crammed into every nook and cranny. Each card has a separate job and all are interconnected. Huge 2in x 2in chips abound, processing and associated memory chips are everywhere, and the bottom 'floor' even contains two multi-chip modules (MCMs) with four separate chips each. These MCMs measure 2in x 2in and are designed to reduce the physical space taken up by external pin connections. The top card contains a long (4.5in) video connector designed for eventual Print to video direct video recording, while a second fan built into the system case is positioned at 45 degrees to blow air over the whole assembly.

The job of turning CPU-generated 3D data into a picture that looks three dimensional to the human eye is not trivial. Particularly complex is the calculation of depth and lighting among the other visual components which have to be computed. Making the object in the picture move smoothly at speed takes real horsepower, which is where the Indigo2 excels, producing spectacular 24-bit colour 1280 x 1024 graphics.

Data comes in over the GIO64 bus connection on the bottom card and enters the command engine and geometry sequencer. It is then split into eight separate floating point data paths and processed in the eight separate Geometry Engines in parallel. These engines are the eight custom RISC chips inside the MCMs. The 3D data and co-ordinates are then fed into two separate raster engines on the middle card. The two engines, again working in parallel, rasterise the data for presentation on a two dimensional display, pass it through to the top card, which contains the frame buffers, VRAM and bitmaps, and outputs the image to the monitor. The monitor itself is a beautifully sharp 19in Trinitron based 1280 x 1024 Silicon Graphics device.

Running IRIX (SGI's Unix), the graphics power was simply the most stunning we have ever seen. Images, such as the Mustang aircraft shown on the screenshot, could, using the mouse, not only be slowly rotated but set spinning in a high speed tumble. The processing power required to achieve this with a remotely lit complex object while displaying a smooth movement is substantial, but the Indigo2 didn't even blink.


The stunning Silicon Graphics Indigo2 can't fail to impress and its graphics capabilities are on a different planet from the world of PC clones. For some very lucky engineers and scientists the Indigo2 will be their own personal desktop machine. The rest of us will just have to dream.

The Indigo2 costs 34,000 UKP.


[obviously, this specs list is out of date; it does not mention later processors such as the R8000 or R10000, larger disks released in the following years (eg. 4.5GB SCSI-2 and 9.1GB UltraSCSI), other graphics options such as XL/XZ/GR3-Elan or IMPACT, or the various video option cards such as IMPACT Video. See the main SGI index for details on other Indigo2-related items]

Silicon Graphics Indigo2:

Processor:        MIPS 100MHz R4000SC
                  upgradable to 150MHz R4400

RAM:              96MB (expandable to 384MB)

Hard disk:        236MB

Storage options:  DAT drive, 3.5in floppy drive

Graphics:         Extreme Graphics subsystem

Interfaces:       Parallel, serial, SCSI 2, Ethernet
                  (AUI and lOBase-T), stereo/quadrophonic audio,
                  microphone, audio in, audio out, headphones,
                  digital in/out sound

Expansion:        Four EISA slots, two G1064 connectors (three
                  EISA slots and two G1064 connectors obscured
                  by Extreme Graphics subsystem)

Dimensions:       19in x 19in x 5in

Ian's SGI Depot: FOR SALE! SGI Systems, Parts, Spares and Upgrades

(check my current auctions!)
[WhatsNew] [P.I.] [Indigo] [Indy] [O2] [Indigo2] [Crimson] [Challenge] [Onyx] [Octane] [Origin] [Onyx2]
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