I'm fairly sure they arn't using clustering, I've seen one of their boxes (this one was a 16x box) and I don't remember seeing any networking hardware there. I'm about 99% sure that this is a real shared memory machine. The Unisis rep I talked to said they can do this with any IA32 CPU you want to use (probably just Athlon/Pentium I'm sure). That's what Unisis is good at, comming up with interesting propriatary solutions.
<< Clusters, you can make a cluster w/ virtually limitless CPUs with the right interfacing. Just look at ASCI White >>