Guest Editors’ Editorial: Special Issue on the Second International Workshop on Microgrids

Arrays and streams, this is what multi-/manycore computing could soon be all about. Indeed array processing is the basis of much DSP, machine graphics and multimedia, while streams are a universal glue that keeps processing pipelines chugging away at full speed. Both possess regularity and both are amenable to heterogeneity. The regularity of arrays is spatial, and of streams temporal. Heterogeneity is a requirement that stems from specialisation of computing and communication resources according to stable patterns of usage. The regularity makes it possible to develop compiler optimisations and hierarchical abstractions to achieve both expressiveness and performance. But it is heterogeneity that gives computing platforms their adaptivity and improves the ability to specialize at run time, when the power of static analyses and optimisations has been exhausted. The second Microgrids Workshop that took place in Hertfordshire in December 2007 explored the issues of regularity and heterogeneity at great length. Out of 2days of talks, four presentations have been selected for publication as journal papers, for which extended versions have been solicited from the authors. After substantial revisions, we present them here in a special issue of IJPP. The motifs of array computing and stream processing permeate all four publications. The first, “Compilation techniques for high level parallel code” contributed by authors from the AMD Corp., ClearSpeed and XMOS, the latter two being parallel computing specialist ventures, focuses on retargeting existing compilers towards dataparallel computing platforms. This is done by extending the datatypes of conventional C by attributes that indicate whether a particular C statement is to be executed on each processor element or only once by the master thread. For a distributed control statement this introduces heterogeneity, which is the focus of this work. Heterogeneity