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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
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