Looking Back on Recovery Blocks and Conversations

Our 1975 paper “System Structure for Software Fault Tolerance” introduced “Recovery Blocks” (a backward error recovery strategy for use in isolated processes), the “Domino Effect” (the problem that a single error could cause multiple interacting processes with uncoordinated error recovery strategies to lose all their recovery capability) and “Conversations” (an error recovery strategy for interacting processes motivated by the danger of the domino effect). This retrospective account describes how these ideas were developed by the Newcastle group and its collaborators, and what further research ensued. A tentative assessment is then provided of the impact of this research.