  Commercial graphics processors (GPUs) have high compute capacity at very low
cost, which makes them attractive for general purpose scientific computing. In
this paper we show how graphics processors can be used for N-body simulations
to obtain improvements in performance over current generation CPUs. We have
developed a highly optimized algorithm for performing the O(N^2) force
calculations that constitute the major part of stellar and molecular dynamics
simulations. In some of the calculations, we achieve sustained performance of
nearly 100 GFlops on an ATI X1900XTX. The performance on GPUs is comparable to
specialized processors such as GRAPE-6A and MDGRAPE-3, but at a fraction of the
cost. Furthermore, the wide availability of GPUs has significant implications
for cluster computing and distributed computing efforts like Folding@Home.
