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Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. Abstract Distributed Shared Memory (DSM) approach provides the illusion of a global shared address space by implementing a layer of shared memory abstraction on a physically distributed memory system. In this paper, we present DSM-SP2, a software distributed shared memory system built on IBM SP2, a distributed memory machine. DSM-SP2 is implemented completely in software as a set of user-level library routines on top of the AIX operating system without requiring any modiications to the operating system or any additional compiler support. The salient features of DSM-SP2 are: (i) it implements lazy release consistency model with hybrid coherence protocol to reduce the communication overheads; (ii) it allows multiple concurrent writers to minimize the effects of false-sharing; (iii) to reduce the DSM overheads and the idling time of processes, the DSM-SP2 implementation allows multiple processes per node; and (iv) it implements a new synchronization primitive called conditional lock acquire/release for eeective simple producer-consumer type of synchronization. Detailed performance measurements for three benchmark programs namely, Water, Jacobi and Tomcatv are reported .