GRAPE-5: A special-purpose computer for N-body simulations

We have developed a special-purpose computer for gravitational many-body si mulations, GRAPE-5. GRAPE-5 accelerates the force calculation which dominat es the calculation cost of the simulation. All other calculations, such as the time integration of orbits, are performed on a general-purpose computer (host computer) connected to GRAPE-5. A GRAPE-5 board consists of eight cu stom pipeline chips (G5 chip) and its peak performance is 38.4 Gflops. GRAP E-5 is the successor of GRAPE-5. The differences between GRAPE-5 and GRAPE- S are: (1) The newly developed G5 chip contains two pipelines operating at 80 MHz, while the GRAPE chip, which was used for GRAPE-S, had one at 20 MHz . The calculation speed of GRAPE-5 is 8-times faster than that of GRAPE-5. (2) The GRAPE-5 board adopted a PCI bus as the interface to the host comput er instead of VME of GRAPE-3, resulting in a communication speed one order of magnitude faster. (3) In addition to the pure 1/r potential, the G5 chip can calculate forces with arbitrary cutoff functions, so that it can be ap plied to the Ewald or (PM)-M-3 methods. (4) The pairwise force calculated o n GRAPE-5 is about 10-times more accurate than that on GRAPE-3. On one GRAP E-5 board, one timestep with a direct summation algorithm takes 14 (N/128 k )(2) seconds. With the Barnes-Hut tree algorithm (theta = 0.75), one timest ep can be done in 15(N/10(6)) seconds.