• Transfer data between compute nodes by message-passing libraries

• Move data between external I/O sources and local disk

The key parameters that define switch performance are latency the overhead needed to deliver the first element in sequence of data, and bandwidth the rate at which data flow.

Keys to performance:

• The latency penalty is large enough to degrade the performance of an otherwise efficient application. For parallel jobs, send fewer but larger messages to avoid this penalty. It is possible, for example, to combine the results of several calculations into a single buffer and wait until all calculations are complete before sending the buffer.

• Employ the VIA protocol for all production runs.