InfiniteReality4 (aka IR4) is not the same thing as Onyx4 Ultimate
Vision (aka Onyx4).
IR4 was the last of a series of IR graphics sets. Check the forum
archives and usenet archives for discussions on the various flavors
of IR. All flavors of IR, including IR4, use Xsgi. InfiniteReality
first came out with the big black Onyx, then Onyx2, and later
Origin/Onyx3000 and Origin/Onyx300 and 350. IR uses it's own huge
G-Brick card cage and several massive circuit boards. A fully
populated IR4 pipe has 1 GB of TRAM and 10 GB of frame buffer memory.
IR3 and IR4 use the same geometry card, so their geo performance is
the same. IR4 has faster raster managers, so its fillrate is faster
than IR3. You can even use IR4 graphics in an Onyx2 if you so desire.
The cardcage and card support is the same.
Onyx4 is basicly an Origin 350 host connected to additional
Origin350-looking bricks containing graphics cards and/or more CPUs.
The graphics cards are ATI FireGL X1 with 256 MB of shared memory.
These are AGP 8X cards, however they are interfaced via PCI at AGP 1X
speeds (read up on the AGP specs, this is easy to do). This is a bit
of a bottleneck, but isn't too bad if you're using display lists and
aren't doing a bunch of glreadpixels(). The new Prism systems are
similar, however they use Altix 350 and native AGP 8X to interface
newer ATI FireGL cards. Onyx4 and Prism use XFree86. I believe Onyx4
uses Free86 4.2, I don't know which version Prism uses, it's probably
a newer version.
To add to the confusion, there was also ?InfinitePerformance? which
was an Onyx 3000 series brick that could contain several V12
?pipelets?. Like VPro on Octane, InfnitePerformance uses Xsgi.