You got it wrong. Sgi is using a hypervisor to trick the linux kernel into believing it is running a single smp server, when it is in fact a cluster. ScaleMP also use the same approach, they also have a 2048 cpu linux server, but they are also running a cluster. These clusters have awful latency to nodes far away, they may look like single image, but it is not. They are only used for parallell HPC workloads. Google on ScaleMP too, and see it also uses a software hypervisor tricking linux kernel into running a single server. These servers are clusters, and unusable as smp single servers.
UPDATE: here is a link on the similar clustered server ScaleMP sells (2048 cores, 64TB RAM):
"....Since its founding in 2003, ScaleMP has tried a different approach. Instead of using special ASICs and interconnection protocols to lash together multiple server modes together into a shared memory system, ScaleMP cooked up a special hypervisor layer, called vSMP, that rides atop the x64 processors, memory controllers, and I/O controllers in multiple server nodes. Rather than carve up a single system image into multiple virtual machines, vSMP takes multiple physical servers and – using InfiniBand as a backplane interconnect – makes them look like a giant virtual SMP server with a shared memory space...."