Using passive replicates in Delta-4 to provide dependable distributed computing

As part of the European Strategic Programme for Research in Information Technology (ESPRIT), the Delta-4 project is seeking to define an open, fault-tolerant, distributed computing architecture. The Delta-4 approach to fault tolerance is based on the replication of software components on distinct host computers. Both active and passive replication strategies are contained within the framework of Delta-4. The philosophy behind the mechanisms used within the passive replication paradigm is presented. In the Delta-4 approach, backward error recovery is achieved by integrating checkpointing with interprocess communication. This approach is seen to be applicable to both deterministic and nondeterministic programs. A description is also given of the implementation of such a system within the overall Delta-4 framework.<>