Up to this point we have considered the subject of parallel computing as a series of almost separated facets – paradigms, languages, processor design, etc. – each of which can be examined in isolation. Of course, in arriving at the design of any real system, be it commercial or prototype, this approach is very far from the true manner of proceeding. In real system design, the watchword is usually compromise – compromise between specific and general applicability, compromise between user friendliness and efficiency in programming, compromise between the demands of high performance and low cost. No imaginary design exercise can do justice to the complexity or difficulty of this process, because the constraints in imaginary exercises are too flexible. In order to see how the various design facets interact, we need to examine real cases. This is the purpose of this chapter.

In it, I present a series of short articles concerning specific machines, each of which has been contributed by an author intimately concerned with the system in question. The brevity has been occasioned by the limited space available in a book of this sort, but it has had the beneficial effect of ensuring that the authors have concentrated on those areas which they consider to be important. Again, because of limited space I have curtailed the number of these contributions, although this has meant that some aspects of the subject remain unconsidered.