Dont hypercubes of the SGI Origin design decrease system bandwidth with increasing size, meaning a fabric based on this design cannot adequately scale?
The hierarchical fat hypercube topology does not “scale down” as nodes are added, provided that the metarouters used by the system between hypercubes increase in dimension as the system grows precisely the pattern followed by SGI engineers. For example, taking a 1,024 processor system built with this architecture and cutting it in two (bisection) yields 8 processors per connection, exactly the same bisection bandwidth as a similarly connected system of 16 or 32 processors. The key is to increase the dimensionality of the metarouter as the system grows. For example, a 128 processor Origin uses 8 2D metarouters (essentially rings), but a 1,024 processor Origin will use 8 5D Hypercubical metarouters. It should added that this use of metarouters will be advantageous when the interconnects are distributed through a building, though thats 5 years off. As for bristling (or the similar topology of cube connected cycles) this does indeed impact bandwidth per processor, hence it is wise to decid
