Editorial: Special Issue on Extreme Scale Parallel Architectures and Systems

High-performance computing (HPC) has embarked into the Petascale era and efforts are already on-going towards further increasing the peak performance of supercomputing systems. The advancement of computing to the Exascale era is of paramount importance to computational science – including its domainspecific angles – for responding promptly to a variety of medical, environmental, societal, engineering and global sustainability open problems. In parallel, various lines of business across sectors are becoming increasingly dependent on gaining valuable insights out of processing large volumes of data. Current trends unveil an exponential rate of increase in the volume of available and meaningful to process data, e.g. as a result of the penetration of smart mobile devices into various facets of life and the installation of sensors/actuators and connectivity modules to a disparity of electronic end-points that generate continuous streams of data. And while supercomputing has traditionally focused on serving computational science problems, it is now clear that the technical requirements posed by large-scale data-science applications should also be embraced as a target throughout the design of Exascale computers. As it is probably inherent in every advancement of state of the art bymultiple orders of magnitude, embarking to the Exascale era is confrontedwith various technical challenges. Aggravating things more, many of the roadblocks to overcome along the roadmap towards Exascale are unique to this advancement – e.g. they are not shared with the challenges faced during advancement to Petascale – and in some cases they cannot be addressed by solely evolving (e.g. scaling) state of the art due to hitting upon fundamental limitations of existing approaches. Not exhaustively listing, parts of these challenges are: exposing extreme scale parallelism, power efficiency, providing for sufficient resilience and efficient data-movement at extreme-scale. In addition, strong focus needs also to be put on evolving or taking clean slate approaches to developing the necessary research methods and tools for evaluating approaches in all aspects of Exascale research and development. In alignment with the frontier problems in Supercomputing, the papers included in the present Future Generation Computer Systems Special Issue on Extreme Scale Parallel Architectures and Systems present latest approaches addressing the top priority list items in the Exascale agenda, specifically: resilience, data movement, efficient extreme scale system simulation and system codesign. Original results are presented, together with tools and guidelines on how to have this new knowledge and toolset directly impact the design and implementation of a future Exascale machine. The first paper in this Special Issue, authored by Richard Barrett et al. and titled ‘‘Exascale Design Space Exploration and Codesign’’, focuses on the use of ‘‘mini-applications’’ as a valuable