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We proposed a computer with low-level parallelism as one of the basic computer architectures and built a large scale experimental system called QA-2. By low-level parallelism, we mean that a long-word instruction controls simultaneously many ALUs, busses, registers and memories in a mode of fine-grained parallelism. The QA-2 employs a 256-bit instruction by which four different ALU operations, four memory accesses to different/continuous locations and one powerful sequence control are all specified and performed in parallel. If many simultaneously executable operations are detected and embedded in one instruction at compile time, this type of computer can provide a high-degree of performance for a wide variety of applications. This paper describes the architectural benefits and limitations of low-level parallelism in performing 3-D color image generation and interpreting Prolog/Lisp programs. The hardware organization with four ALUs, which are actually implemented in the QA-2, is verified to be adequate. In fact, nearly three out of four ALUs can work in parallel. Any architecture with more than four ALUs can not achieve a significant degree of performance enhancement. This paper also shows the degree of performance improvement achieved by the techniques such as ALU chaining and highly-structured sequence control mechanisms. As compared with the IBM 370 architecture, the QA-2 can generate 3-D color images in 1/5 of dynamic instruction steps. The compiler version of Prolog machine on the QA-2 is as fast (45K LIPS) as the ICOT's PSI. From all results, we expect that the QA-2 is a high-performance computer which will be utilized in the future personal computing environment.

A computer with low-level parallelism QA-2: its applications to 3-D graphics and Prolog/Lisp machines