ILLIAC IV - Aftermath

Aftermath

Although the ILLIAC travails ended in uninspiring results, attempts to understand the reasons for the difficulties of the ILLIAC IV architecture pushed forward research in parallel computing. During the 1980s a number of companies used the same approach to build even more parallel machines, with compilers that could make better use of the parallelism. The Thinking Machines CM-1 and CM-2 are excellent examples of the "classic" ILLIAC IV concept, although they also included far better interconnectivity between their PE's in order to avoid data bottlenecks that reduced the problem set suitable for use on the ILLIAC.

Most supercomputers of the era took another approach to higher performance, using a single very high speed vector processor. Similar to the ILLIAC in concept, these processor designs loaded up many data elements into a single custom processor instead of a large number of low-powered ones. The classic example of this design is the Cray-1, which had performance similar to the ILLIAC. There was more than a little "backlash" against the ILLIAC design as a result, and for some time the supercomputer market looked on massively parallel designs with disdain, even when they were successful. As Seymour Cray famously quipped, "If you were plowing a field, which would you rather use? Two strong oxen or 1024 chickens?"

But time has proven the ILLIAC approach to be the better one for almost all scientific computing. Today, supercomputers are almost universally made up from large numbers of commodity computers, precisely the concept that the ILLIAC pioneered. Progress in compiler technology explains much of this, although the rapid, and perhaps unexpected, continued improvement in microprocessor design rendered custom vector designs slower in most workloads.