The performance of a file system depends strongly on the characteristics of the files stored in it. This paper discusses the collection, analysis and interpretation of data pertaining to files in the computing environment of the Computer Science Department at Carnegie-Mellon University (CMU-CSD). The information gathered from this work will be used in a variety of ways: 1. As a data point in the body of information available on file systems. 2. As input to a simulation or analytic model of a file system for a local network, being designed and imlemented at CMU-CSD [1]. 3. As the basis of implementation decisions and parameters for the file system just mentioned. 4. As a step toward understanding how a user community creates, maintains and uses files.