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In this paper, we propose and evaluate a cluster-based network server called PRESS. The server relies on locality-conscious request distribution and a standard for user-level communication to achieve high performance and portability. We evaluate PRESS by first isolating the performance benefits of three key features of user-level communication: low processor overhead, remote memory accesses, and zero-copy transfers. Next, we compare PRESS to servers that involve less intercluster communication, but are not as easily portable. Our results for an 8-node server cluster and five WWW traces demonstrate that user-level communication can improve performance by as much as 52 percent compared to a kernel-level protocol. Low processor overhead, remote memory writes, and zero-copy all make nontrivial contributions toward this overall gain. Our results also show that portability in PRESS causes no throughput degradation when we exploit user-level communication extensively.