Supercomputing at KFA Jülich: Experiences and Applications on CRAY X-MP

KFA Jülich is one of the largest big-science research centers in Europe. At KFA, computational science based on supercomputer techniques has received high priority for many years. Primarily, CRAY supercomputer power has been exploited in the single processor mode by applying vectorization and optimization techniques to numerical kernels and large applications. However, on the multiprocessor vector-supercomputers CRAY X-MP and Y-MP, parallelism — beyond vectorization — can be exploited by multitasking. With increasing number of powerful processors, multitasking strategies like macrotasking, microtasking, and autotasking will become more important and profitable to utilize these multiprocessor systems efficiently. Multitasking results and experiences have been gained by applying these modes to linear-algebra and non-numerical algorithms as well as to large codes. While comparing the results and the concepts of multitasking, the problems, benefits, and perspectives of multitasking programming will be discussed.