All systems will fail. The question is not whether some mishap will happen, but rather what to do when it does occur. In this Turing Award address, Corbató examines the problems associated with the development of ambitious or complex systems and identifies why they always fail. Sources of complexity that contribute to this failure include the number of personnel required, the levels of management, the lack of willingness to report bad news, and the inability of any one person to understand the complete system. He offers solutions to each of these problems, including simplicity in design, use of metaphors, constrained languages for design, anticipation of errors, design for modification, cross education of team members, and learning from past mistakes.

Frenkel’s interview, conducted after Corbató’s Turing Award lecture, complements it. The questions and answers provide a comprehensive overview of the development of the time-sharing systems CTSS and Multics, and a good overview of some of the individuals involved in these efforts. One of the most interesting parts of this interview is the support (or lack of interest) of some of the major computer manufacturers in the 1960s, including GE, IBM, and DEC. The support of Bell Labs for Multics and its eventual disengagement are examined. The relationship between UNIX and Multics is discussed in some detail, as are the problems in the development of these systems. The discussion concludes with an examination of the transition from mainframes to workstations and PCs. This interview will appeal to people interested in the historical development of time-sharing systems.