Origin 2000 network

• Each router has six pairs of 1.56 GB/s unidirectional links; two to nodes (bristled), four to other routers
• 41 ns pin to pin latency
• Four virtual networks: request, reply, priority, I/O

Origin 2000 I/O

• Any processor can access I/O device either through uncached ops or through coherent DMA
• Any I/O device can access any data through router/hub

Origin directory

• Directory formats
  • If exclusive in a cache, entry contains processor number (not node number)
  • If shared, entry is a bitvector of sharers where each corresponds to a node (not a processor)
    • Invalidations sent to a node is broadcast to both processors by hub
  • Two sizes
    • 16-bit format (up to 32 processors), kept in DRAM
    • 64-bit format (up to 128 processors), kept in extension DRAM
    • For machine sizes larger than 128 processors the protocol is coarse-vector (each bit is for 8 nodes)
    • Machine can switch between BV and CV dynamically