HP XC System 2.x Software - Manual (Page 55)

3.9.4 Communication Between Nodes
On the HP XC system, processes in an MPI application run on compute nodes and use
the system interconnect for communication between the nodes. By default, intranode
communication is done using shared memory between MPI processes. Refer to Chapter 8 for
information about selecting and overriding the default system interconnect.
Developing Applications 3-15