Starfire: extending the SMP envelope

Like most multiboard systems, Starfire has a two-level interconnect. The on-board interconnect conveys traffic from the processors, SBus cards, and memory to the off-board address and data ports. The centerplane interconnect transfers addresses and data benveen the boards. Memory accesses always traverse the global interconnect, even if the requested memory location is physically on the same board. Addresses must be sent off board anyway to accomplish global snooping. Data transfers are highly pipelined, and local shortcuts to save a few cycles would have unduly complicated the design. As with the rest of the Ultra server family, Starfire´s uniform-memory-access time is independent of the board where memory is located