The CAP project has included the design and construction of a computer with an unusual and very detailed structure of memory protection, and subsequently the development of an operating system which fully exploits the protection facilities. The present paper passes the work in review and draws conclusions about good and bad aspects of the system. The basic architecture of the CAP machine is described in [1] and a largely prospective description of the protection system is given in [2].   The project was started as an experiment in hardware memory protection. A computer was to be designed in which operating system development was easy, in which ruggedness was produced by a much more fine-grained network of firewalls than was (or is) usual, and in which the full range of protection facilities was available to the writers of subsystems. Simplicity of mechanism was a very important goal, although some emphasis was placed on flexibility of protection policy.
['Roger M. Needham']
The CAP project - an interim evaluation