The 3B20D Processor is designed to be a high-availability system for utilization in electronic switching systems. This high availability translates into the development ofnumerous features and capabilities for the 3B20D that distinguish it from otherprocessors. The reliability objectives for the processor are described and related to the subsystems that have been developed to meet each objective. This article discusses processor and peripheral fault recovery, system integrity, and other software subsystems that provide the high availability and maintainability for the processor.FAULT DETECTION AND RECOVERY 351