A VAXcluster is a highly available and extensible configuration of VAX computers that operate as a single system. To achieve performance in a multicomputer environment, a new communications architecture, communications hardware, and distributed software were jointly designed. The software is a distributed version of the VAX/VMS operating system that uses a distributed lock manager to synchronize access to shared resources. The communications hardware includes a 70 megabit per second message-oriented interconnect and an interconnect port that performs communications tasks traditionally handled by software. Performance measurements show this structure to be highly efficient, for example, capable of sending and receiving 3000 messages per second on a VAX-11/780.