GRAPE project: special-purpose computers for many-body simulations

In this paper, we overview the GRAPE (GRAvity piPE) project to develop and use special-purpose computers for astrophysical many-body simulations. First, we discuss the trends in semiconductor technology and computer architecture, and discuss merits and demerits of special-purpose computers. The main advantage of the special-purpose systems is the possibility to utilize a much higher fraction of available silicon to actually do calculations. Most of the silicon on general-purpose microprocessors are now used for control logics and cache, in other words, to assure the generality. As an example, we describe our GRAPE project. In astrophysical many-body simulations, practically all computer time is spent to evaluate particle-particle interactions. This is because the gravitational interaction between astrophysical bodies is a long-range interaction and we cannot apply a cutoff. The basic idea behind the GRAPE project is let the special-purpose computer perform only the evaluation of the particle-particle interaction. All the rest of the calculation, such as the time integration of the orbits of particles, I/O, and diagnostics are handled by a general-purpose host computer. This partitioning has many important advantages, such as the ease of the development of the hardware, the flexibility of the overall system and long lifetime of the system. The newest machine, GRAPE-6, which will be completed soon, will provide the peak speed exceeding 100 Tflops, for the development cost of less than 5 M dollars. (C) 2001 Elsevier Science B.V. All rights reserved.