There were parallel computers before 1980, but they did not have a widespread impact on scientific computing. The activities of the 1980s had a much more dramatic effect. Still, a few systems stand out as having made significant contributions that were taken advantage of in the 1980s. The first is the Illiac IV [Hockney:81b]. It did not seem like a significant advance to many people at the time, perhaps because its performance was only moderate, it was difficult to program, and had low reliability. The best performance achieved was two to six times the speed of a CDC 7600 . This was obtained on various computational fluid dynamics codes. For many other programs, however, the performance was lower than that of a CDC 7600, which was the supercomputer of choice during the early and mid-1970s. The Illiac was a research project, not a commercial product, and it was reputed to be so expensive that it was not realistic for others to replicate it. While the Illiac IV did not inspire the masses to become interested in parallel computing, hundreds of people were involved in its use and in projects related to providing better software tools and better programming languages for it. They first learned how to do parallel computing on the Illiac IV and many of them went on to make significant contributions to parallel computing in the 1980s.
The Illiac was an SIMD computer-single-instruction, multiple-data architecture. It had 32 processing elements, each of which was a processor with its own local memory; the processors were connected in a ring. High-level languages such as Glypnyr and Fortran were available for the Illiac IV. Glypnyr was reminiscent of Fortran and had extensions for parallel and array processing.
The ICL Distributed Array Processor (DAP) [DAP:79a] was a commercial product; a handful of machines were sold, mainly in England where it was designed and built. Its characteristics were that it had either 1K or 4K one-bit processors arranged in a square plane, each connected in rectangular fashion to its nearest neighbors. Like the Illiac IV, it was an SIMD system. It required an ICL mainframe as a front end. The ICL DAP was used for many university science applications. The University of Edinburgh, in particular, used it for a number of real computations in physics, chemistry, and other fields [Wallace:84a;87a]. The ICL DAP had a substantial impact on scientific computing culture, primarily in Europe. ICL did try to market it in the United States, but was never effective in doing so; the requirement for an expensive ICL mainframe as a host was a substantial negative factor.
A third important commercial parallel computer in the 1970s was the Goodyear Massively Parallel Processor (MPP) [Batcher:85a], [Karplus:87a, pp. 157-166]. Goodyear started building SIMD computers in 1969, but all except the MPP were sold to the military and to the Federal Aviation Administration for air traffic control. In the late 1970s, Goodyear produced the MPP which was installed at Goddard Space Flight Center, a NASA research center, and used for a variety of scientific applications. The MPP attracted attention because it did achieve high speeds on a few applications, speeds that, in the late 1970s and early 1980s, were remarkable-measured in the hundreds of MFLOPS in a few cases. The MPP had 16K one-bit processors, each with local memory, and was programmed in Pascal and Assembler.
In summary, the three significant scientific parallel computers of the 1970s were the Illiac IV, the ICL DAP, and the Goodyear MPP. All were SIMD computers. The DAP and the MPP were fine-grain systems based on single-bit processors, whereas the Illiac IV was a large-grain SIMD system. The other truly significant high-performance (but not parallel) computer of the 1970s was the CRAY 1, which was introduced in 1976. The CRAY 1 was a single-processor vector computer and as such it can also be classified as a special kind of SIMD computer because it had vector instructions. With a single vector instruction, one causes up to 64 data pairs to be operated on.
There were significant and seminal activities in parallel computing in the 1970s both from the standpoint of design and construction of systems and in the actual scientific use of the systems. However, the level of activity of parallel computing in the 1970s was modest compared to what followed in the 1980s.