Title: Comparing the Performance of Centralized and Distributed Coordination on Systems with Improved Combining Switches (NYU-CS-TR849) Author: Eric Freudenthal and Allan Gottlieb Abstract: Memory system congestion due to serialization of hot spot accesses can adversely affect the performance of interprocess coordination algorithms. Hardware and software techniques have been proposed to reduce this congestion and thereby provide superior system performance. The combining networks of Gottlieb et al. automatically parallelize concurrent hot spot memory accesses, improving the performance of algorithms that poll a small number of shared variables. The widely used MCS distributed-spin algorithms take a software approach: they reduce hot spot congestion by polling only variables stored locally. Our investigations detected performance problems in existing designs for combining networks and we propose mechanisms that alleviate them. Simulation studies described herein indicate that a centralized readers writers algorithms executed on the improved combining networks have performance at least competitive to the MCS algorithms.