A method and apparatus for sending and receiving messages between nodes on a compute cluster is provided. Communication between nodes on a compute cluster, which do not share physical memory, is performed by passing messages over an I/O subsystem. Typically, each node includes a synchronization mechanism, a thread ready to receive connections, and other threads to process and reassemble messages. Frequently, a separate queue is maintained in memory for each node on the I/O subsystem sending messages to the receiving node. Such overhead increases latency and limits message throughput. Due to a specialized coprocessor running on each node, messages on an I/O subsystem are sent, received, authenticated, synchronized, and reassembled at a faster rate and with lower latency. Additionally, the memory structure used may reduce memory consumption by storing messages from multiple sources in the same memory structure, eliminating the need for per-source queues.