I O IN PARALLEL APPLICATIONS - THE WEAKEST LINK/

Parallel computers are increasingly being used to run large-scale appl ications that also have huge input/output (I/O) requirements. However, many applications obtain poor I/O performance on modem parallel machi nes. This two-part special issue of the International Journal of High Performance Computing Applications contains papers that describe the I /O requirements and the techniques used to perform I/O in real paralle l applications. The authors first explain how the I/O application prog ram interface (API) plays a critical role in enabling such application s to achieve high I/O performance. They describe how the commonly used UNIX I/O interface is inappropriate for parallel I/O and how an expli citly parallel API with support for collective I/O can help the underl ying I/O hardware and software perform I/O efficiently. They then desc ribe MPI-IO, a recently defined, standard, portable API specifically d esigned for high performance parallel I/O. They conclude with an overv iew of the papers in Part 1 and Part 2 of this special issue.