This is a diagram illustrating parallel I/O with CGNS. Across the top of this figure are five boxes, labeled P00 through P04, representing five processors. Below that are three boxes stacked vertically, labeled from top to bottom as:

There are double-sided arrows between each of the five processor boxes and the topmost of these three boxes, representing data flow in both directions. Across the bottom of the figure is a box labeled "Parallel File System". There are five double-sided arrows between this box and the box above it labeled "MPI-I/O", again representing data flow in both directions.