SGI's Indy is the most ubiquitous SGI workstation around. It is small, quiet, and powerful for its time, with a nice range of available processors and graphics solutions. They are readily available on the second (or third, or fourth) hand market for less than twenty dollars in working condition, though shipping on these machines (which are built from heavy plastic and thick sheet steel as were all Unix workstations at the time.)
The most common processor for the Indy is probably the R4000, but R4400s are not uncommon, nor is the low budget version of that chip, the R4600. The R5000 processors, however, are uncommon. Further, they are not that much faster than the R4400 (and come at a lower clock speed) except in operations where cache is especially advantageous, or when doing a lot of floating point math. If you are looking to pick up an Indy, unless you see a great deal on an R5000 model, the R4400 is what you want.
The Indy is well-known amongst geeks not only for its cute blue case, jazzy rom-based startup sound, and the shiny SGI logo emblem on the front, but also for its tremendous I/O capabilities. The system has a plethora of ports which helped make it popular:
Looking at the back and going more or less left to right, top to bottom, the first thing you will see is the two expansion slots, which run about halfway across the back of the case. Below the first (leftmost) slot is a 3 pin Mini-Din port for LCD shutter goggles, usable at higher refresh rates to generate fairly believable stereo images. Next to it is a SGI-pinout 13W3 connector used for video output. Below these ports are a range of audio connectors, all 1/8" stereo miniplugs: headphone, microphone, line level input, line level output, and line level in/output. Also here is the composite video connector.
Below the next slot is the AUI ethernet connection amidst a couple of rows of ventilation holes. Below this is the S-Video connection, and the IndyCam connector, a video input for the special "IndyCam" video camera, a slick-looking unit with a shutter to cover the lens for privacy which generally came with Indys. To the right of that you will find first the ISDN port and then the RJ45 10baseT ethernet connection, which for most of us will make the AUI connection redundant. The ISDN was common on Unix workstations at the time and was supposedly useful for using your Indy for videoconferencing and working from home, though at least in the USA widespread ISDN adoption trailed the release of the Indy considerably, or never actually came depending on who you talk to.
The final group of connectors, which would be below the third slot if such a thing existed, include PC-style PS/2 keyboard and mouse connectors, and Macintosh-style serial ports. In fact an old Macintosh modem cable (Such as used on all 68k macs) can be utilized on the Indy without issues, so long as it is a cable which supports hardware handshaking. This can be used to access the serial console. To the right of these ports you will find the parallel port and the SCSI port, which uses a SCSI-2 type connector.
To the right of these final ports you will find the power supply. The system is designed such that this is easily replacable, even if you were to install a DC supply, because the entire area of the back of the power supply is uncovered by the case, allowing it to make its own provisions for ventilation and cable position.
Because it is easy to get your hands on one or more Indy workstations for very little money, these systems are one of basically three SGI systems with any kind of decent support for Free/Open Unix variants or workalikes, the others being the Indigo2 and the O2. The indy is well-supported by both linux and netbsd, with the majority of functionality supported, and an openbsd port is reportedly in the works. Most notably absent from all of these is support for the video input/output hardware, and for any graphics console except for the SGI "Newport" graphics cards, which are not 3D accelerated as the XL models are. However the X Window System is supported on Newport, as well as a text console/tty. Linux supports the sound hardware in the Indy as well.
Besides supporting IRIX from 5.2 through 6.5 (the current version at the time of this writing) SGI also assisted RedHat in porting version 7.1 of their linux distribution to the Indy. This can still be downloaded from SGI but is quite naturally unsupported. Newer linux distributions supporting the Indy can be had from gentoo or debian.
The low points of the system are easily its maximum memory expansion (256MB), slow SCSI performance (Fast/Narrow which peaks around 10MB/s) and slow ethernet interface. Not only are other network adapters generally unsupported, but they will usually cost more than the Indy system itself. The up sides include serial console support (9600 baud, no parity, 1 stop bit), low power consumption, quiet operation, minimal footprint (just a little narrower than a component stereo, er, component) and excellent support due to its low cost, another point to recommend it. While they have little purpose (at least while running anything other than IRIX) they are an attractive and inoffensive computer which is fantastic for hobbyists. When equipped with one of the faster processors and nicer graphics boards, they actually become quite a nice workstation at which to sit and run remote X clients.
The Indy enjoyed a fairly long life, being used for all types of work, though generally only in shops which already included SGI computers. Many Unix shops included a token SGI Indy which resulted from their trial of the system as a possible upgrade from their Sun workstations, which generally never happened. The Indy had excellent video capabilities and when coupled with SGI's XFS filesystem which supported guaranteed rate I/O, was an excellent non-linear editing platform for its time, as well as being one of the faster uniprocessor computers of its day. When it was released it was generally either cheaper or faster (depending on the processor module) than a PC clone, and did more as well, but this was the time when PCs were beginning to flourish and the Indy's lead rapidly diminished as PCs became both faster and cheaper, and took on specialized hardware to perform multimedia tasks which once were SGI's exclusive domain.