Simulations of a standard DDM were performed, varying numbers of CPUs each with ten replicates. (a) The speedup, defined as (execution time on 1 CPU)/(execution time on N CPUs), and (b) parallel efficiency, defined as speedup/(N CPUs), are shown for different numbers of CPUs. Because measured execution time varied run to run, the mean parallel efficiency could sometimes exceed 1. Error bars are bootstrapped 95% confidence intervals. Solid black lines indicate data, and dashed green lines indicate the theoretical maximum under noiseless conditions. Confidence intervals in (a) are hidden beneath the markers.