An analysis of the failure statistics of a commercially available fault-tolerant system shows that administration and software are the major contributors to failure. Various approaches to software fault-tolerance are then discussed -- notably process-pairs, transactions and reliable storage. It is pointed out that faults in production software are often soft (transient) and that a transaction mechanism combined with persistent processpairs provides fault-tolerant execution -- the key to software fault-tolerance.

An analysis of the failure statistics of a commercially available fault-tolerant system shows that administration and software are the major contributors to failure. Various approachs to software faulttolerance are then discussed notably process-pairs, transactions and reliable storage. It is pointed out that faults in production software are often soft (transient) and that a transaction mechanism combined with persistent process-pairs provides fault-tolerant execution-- the key to software fault-tolerance. DISCLAIMER This paper is not an "official " Tandem statement on fault-tolerance.