Iterative instructions in the Manchester Dataflow Computer

The authors investigate the nature and extent of the benefits and adverse effects of iterative instructions in the prototype Manchester Dataflow Computer. Iterative instructions are shown to be highly beneficial in terms of the number of instructions executed and the number of tokens transferred between modules during a program run. This benefit is apparent at hardware level, giving significantly reduced program execution times. However, the full benefits are not realized due to interference between lengthy iterative instructions. It is suggested that restructuring of buffers and the function unit array in the prototype hardware configuration can reduce this interference. Other possibilities for improvement are suggested. For example, the slowdown effect observed in hardware speedup curves could be tackled by treating iterative instructions differently from fine-grain instructions. An alternative structure for the processing element in which certain function units are specialized for executing iterative instructions is being investigated in this connection