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We are developing a series of special purpose computers, GRAPE (GRAvity PipE), for gravitational N-body simulations. In gravitational N-body simulations, almost all computing time is consumed in the calculation of gravitational force between particles. GRAPE calculates the forces in a high speed using hardwired pipelines. A host computer, which is connected to GRAPE, sends the positions of particles to GRAPE. Then GRAPE calculates the force exerted on a particle and sends it back to the host computer. Using the force calculated by GRAPE, the host computer integrates the orbits of particles. We have already developed six different machines (GRAPE-1, GRAPE-1A, GRAPE-2, GRAPE-2A, GRAPE-3, and GRAPE-3A). They are divided into two types, i.e., the low-accuracy and the high-accuracy types.
The machines with odd numbers belong to the low-accuracy type. They are designed for the simulations of collisionless systems such as galaxies. GRAPE-3 is a highly parallel system with 48 full-custom LSI chips (GRAPE chip). Each LSI chip has one GRAPE pipeline. The sustained speed of GRAPE-3 is 10 Gflops for a 200,000 particle simulation.
The machines with even numbers belong to the high-accuracy type. They are designed for collisional systems such as globular clusters and proto-planetary system. GRAPE-2A was designed for the application of the molecular dynamics simulations as well as gravitational N-body simulations. GRAPE-2A can calculate the forces of an arbitrary functional form using interpolation tables. The computational speed of GRAPE-2A is 180 Mflops. We are developing highly parallel machine, GRAPE-4, in which many GRAPE pipelines (about 1,600) work in parallel. The planned peak speed of GRAPE-4 is one teraflops. GRAPE-4 will complete by the end of 1994.
