As systems move from the current 10,000-100,000 cores to anticipated numbers of threads exceeding ten million, a key issue is how best to represent multi-level concurrency in the programming environment. Pure MPI may still be useful and efficient at the inter-node level but with core counts per node likely to reach into the hundreds, multi-threading using models such as OpenMP and OpenCL is also required. PGAS languages are attractive in providing the programmer with a high-level abstraction but require considerable compiler and run-time support to be efficiently implemented.

The Shock-Boundary Layer Interaction (SBLI) CFD code was implemented in Coarray Fortran by Ashby and Reid.

Evaluations on the performance of the Co-Array Fortran version on various systems were also performed. Performance on HECToR and ARCHER has been poor and results were presented as a poster at PGAS 2014 attracting considerable sympathy from others with a similar experience.