The parallel processing system -Harray- for scientific computations is introduced. The special features of the -Harray- system described are (1) the Controlled Dataflow (CD flow) mechanism, (2) the preceding activation scheme with graph unfolding, and (3) the visual environment for dataflow program development. The CD flow mechanism, controlling the sequence of execution in two levels-dataflow execution in each processor and control flow execution between processors-is adapted in the -Harray- system. Though dataflow computers are expected to extract parallelism fully from a program, they have many problems, such as the difficulty of controlling the sequence of execution. To solve these problems, the CD flow mechanism is adopted. The preceding activation scheme makes it possible to bypass control dependencies in a program, such as IF-GOTO statements which decrease the parallelism in a program. The flow graph of a program is unfolded to decrease the control dependency and to increase the parallelism. The visual environment helps programmers in the writing and debugging of a dataflow program. The environment consists of a graphical editor of a dataflow graph, and a debugger. These special features of the -Harray- system and its execution mechanism are described.
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