This paper describes Felix - a File Server for an experimental distributed multicomputer system. Felix is designed to support a variety of file systems, virtual memory, and database applications with access being provided by a local area network. Its interface combines block oriented data access with a high degree of crash resistance and a comprehensive set of primitives for controlling data sharing and consistency. An extended set of access modes allows increased concurrency over conventional systems.

This correspondence is concerned with the detection of permanent faults in redundant combinational networks. Fault masking in such networks is examined. A method for determining an optimal test set that will detect all detectable faults is given.

The problem of how to determine minimal sets of tests for single and multiple faults in irredundant combinational circuits is dealt with. It is shown that the "Equivalent Sum of Products" form of the given network contains all the information necessary to derive a min; mal test set. A simple procedure which generates a minimal test set Ts for single faults is described. Fault masking is then studied and it is shown how to find the multiple faults undetected by Ts. Finally a method which derives a nearly minimal multiple fault test set Tm where Ts [mi][/mi] Tm is given.