All programs in the QuickSilver distributed system behave atomically with respect to their updates to permanent data. Operating system support for transactions provides the framework required to support this, as well as a mechanism that unifies reclamation of resources after failures or normal process termination. This paper evaluates the use of transactions for these purposes in a general purpose operating system and presents some of the lessons learned from our experience with a complete running system based on transactions. Examples of how transactions are used in QuickSilver and measurements of their use demonstrate that the transaction mechanism provides an efficient and powerful means for solving many of the problems introduced by operating system extensibility and distribution. © 1991 ACM.