ECMWF Slide 3Porting MPI Programs to the IBM Cluster 1600 The current hardware switch Designed for a previous generation of IBM hardware Referred to as the Colony switch 2 switch adaptors per logical node -8 processors share 2 adaptors -called a dual plane switch Adaptors are multiplexed -software stripes large messages across both adaptors Minimum latency 21 microseconds Maximum bandwidth approx 350 MBytes/s - about 45 MB/s per task when all going off node together