This paper reports an array of measuring tools devised to aid in the implementa tion of a prototypE' computer utility. These tools include special hardware clocks i'md data channels, general purpose programmed probing and recording tools, and specialize d measuremen t facilities . Some particular measuremen ts of interest in a system whlch combines demand paging with multiprogrammin g are described in detail. Where appropriat e, insight into effectiven ess (or lack thereof) of individual tools

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... s provided. In the construction of a modern, complex computer operating system, sophisticated tools are needed to measure what is going on inside the system as it runs. The list of hardware and software tools and techniques used for the measurement of Multics is interesting both from the point of view of what has proved to be important to measure, and what has not. Multics is a project whose intent is to explore the implications of building a comprehensive computer utility. The specific goals of Multics are described in a series of papers written in 1965 1 ; briefly, the objective is to create a computer operating system centered around the ability to share information in a controlled way, and permitting application to a wide variety of computational jobs. A spectrum of user services, including a hierarchical file organization, sharing of information in fore memory, dynamic linking of subroutines and data, parallel processing and device-independent input/output facilities characterize the system, and contribute to a complexity that makes careful instrumentation mandatory. +