This book explains what a supercomputer is and why such a machine is needed to solve challenging problems in science and engineering. The architecture of super computers which distinguishes them from other computers is explained and the need to vectorise programs to make effective use of supercomputers is brought out.

Supercomputer technologies have evolved rapidly since the first commercial-based supercomputer, CRAY-1 was introduced in 1976. In early 1980's three Japanese super computers appeared, and Cray Research delivered the X-MP series. These machines including the later-announced CRAY-2 and NEC SX series created one generation of supercomputers, and the market was spread dramatically. The peak performance was higher than 1 GFLOPS and the compiler improvement was remarkable. There appeared many articles and books that described their architecture and their performance on The late 1980's saw a new generation of supercomputers. several benchmark problems. Following CRAY Y-MP and Hitachi S-820 delivered in 1988, NEC announced SX-3 and Fujitsu announced the VP2000 series in 1990. In addition, Cray Research announced the Y-MP C-90 late in 1991. The peak performance of these machines reached several to a few ten's GFLOPS. The hardware characteristics of these machines are known, but their practical performance has not been well documented so far. Computational Fluid Dynamics (CFD) is one of the important research fields that have been progressing with the growth of supercomputers. Today's fluid dynamic re search cannot be discussed without supercomputers and since CFD is one of the im portant users of supercomputers, future development of supercomputers has to take the requirements of CFD into account. There are many benchmark reports available today. However, they mostly use so called kernels. For fluid dynamics researchers, benchmark test on real fluid dynamic codes are necessary.

Awareness of the need and potential of supercomputers for scientific and engineering research has grown tremendously in the past few years. It has culminated in the Super computer Initiative undertaken two years aga by the National Science Foundation and presently under full development in the United States. Similar initiatives are under way in several European countries and in Japan too. Thus the organization of a symposium on 'Supercomputer Simulations in Chemistry' appeared timely, and such a meeting was held in Montreal (Canada) in August 1985, sponsored by IBM-Kingston and IBM-Canada, and organized by Dr. Enrico Clementi and Dr. Michel Dupuis. In connection with this, IBM's support of the Cornell University Supercomputer Center, several projects in the IBM Research Division, the experimental parallel engine (ICAP) assembled at IBM-Kingston, and the announcement (Fall 1985) of an add-on vector feature to the 3090 IBM mainframe underscore IBM's commitment to high-end scientific/engineering computing. The papers presented in this volume discuss topics in quantum mechanical and statis tical mechanical simulations, both of which test the limits of computer hardware and soft ware. Already a great deal of effort has been put into using vector supercomputers in these two areae. Much more is needed and, without doubt, ie bound to happen. To start, an historical perspective of computational quantum chemistry is provided by Professor Löwdin. The contribution by Ohno and co-workers gives an indication of the present status of Japanese supercomputers. Kutzelnigg et al. , Bauschlicher et al. , and Guest et al.

This volume represents the contributions of the 1989 IABG workshop on supercomputers and chemistry.