A key component for running the climate model I'm using is MPICH. MPICH is an implementation of the MPI (Message Passing Interface) library for supercomputing maintained at Argonne National Laboratory (disclosure: I am a former employee of the lab). The climate model uses MPICH to break down the world into smaller parts and distribute those parts to each CPU. However, these parts must also talk to each other because climate information must move from processor to processor so that each processor knows what's going on around it.