The MPP devices all implement MPI on top of native communication. For the devices whose names start with with ch_, the device uses the simpler channel interface, minimizing the amount of platform-dependent code. For the other devices, the ADI is implemented directly on the native communication library.
For all MPP devices, MPICH uses the native mechanism for starting and managing processes, for handling I/O, etc.
The performance of these MPICH implementations is in most cases very close to that of the underlying communication layer.