We prove an Ω (n log n) lower bound on the number ofnon-busywaiting memory accesses by any deterministic algorithm solving n process mutual exclusion that communicates via shared registers.The cost of the algorithm is measured in the \emph{state change} costmodel, a variation of the cache coherent model. Our bound is tight in this model. We introduce a novel information theoretic proof technique. We first establish a lower bound on the information needed by processes to solve mutual exclusion. Then we relate the amount of information processes can acquire through shared memory accesses to the cost they incur. We believe our proof technique is flexible and intuitive, and may be applied to a variety of other problems and system models.
