Performance degradation by input/output in multiprocessor systems

The performance degradation in multiprocessor systems by input/output has been investigated theoretically for a linear systems configuration and by experiment on two different multiprocessor systems. Processing the results from experiments and from the literature shows a performance degradation of up to an order of magnitude, depending on systems configuration and problem type. Several experiments were run with input/output on a transputer system of selectable dimension D of 1 to 4 with up to 16 processors, running a variety of applications programs in a functional programming language. All results show saturation of systems performance at different optimal processor numbers N. These results are compared with those reported in the literature and with the theory given by the author. Communications factors between 0.8% and 4% without external input/output and between 10% and 33% with input/output, depending on experiment settings, were obtained