Alternative Approaches to Parallel Processing — The Butterfly Plus and Helios Systems

Abstract

The Inmos transputer offers one solution to the difficult problem of implementing parallel systems through the use of point-to-point serial communication links. However, parallel systems can also be constructed using shared memory for interprocessor communication. In this Chapter these two radically different approaches to parallel processing are investigated with respect to real-time control using the Helios Operating system for transputers and the BBN Butterfly Plus computer [33, 34]. The Butterfly Plus computer was chosen for this evaluation as it uses MC68020 processors which are currently the “state-of-the art” in aerospace applications. This provides a benchmark for the transputer and, in addition, the Butterfly uses shared memory for interprocessor communication. Thus, a comparison of a parallel system of MC68020’s using shared memory for communication with transputers which use point-to-point channels for communication can be performed in order to evaluate the advantages and disadvantages of each technique. C was chosen as the programming language for the investigation as the C compiler is optimised, producing faster code, thus giving a fairer representation of the power of the Butterfly Plus. This also enables a comparison to be performed with the simulation implemented in C on transputers using the Helios operating system [35].