Improved Optimal Shared Memory Simulations, and the Power of Reconfiguration

W e present time-processor optimal randomized algorithms for simulating a shared memory machine ( E R E W P R A M ) on a distributed memory machine (DMM). The first algorithm simulates each step of an n-processor E R E W P R A M on an n-processor DMM with O( l ~ ~ ~ ~ ~ o ~ n ) delay with high probability. This simulation is work optimal and can be made timeprocessor optimal. The best previous optimal simulations require o(log1ogn) delay. We also study reconfigurable DMMs which are a “complete network version” of the well studied reconfigurable meshes. We show an algorithm that simulates each step of an nprocessor E R E W P R A M on an n-processor reconfigurable DMM with only O(log* n) delay with high probability. We further show how to make this simulation time-processor optimal.