Observations on the development of an operating system

The development of Pilot, an operating system for a personal computer, is reviewed, including a brief history and some of the problems and lessons encountered during this development. As part of understanding how Pilot and other operating systems come about, an hypothesis is presented that systems can be classified into five kinds according to the style and direction of their development, independent of their structure. A further hypothesis is presented that systems such as Pilot, and many others in widespread use, take about five to seven years to reach maturity, independent of the quality and quantity of the talent applied to their development. The pressures, constraints, and problems of producing Pilot are discussed in the context of these hypotheses.