Department of Computer Science and Technology

Technical reports

Evaluation of a protection system

Douglas John Cook

181 pages

This technical report is based on a dissertation submitted April 1978 by the author for the degree of Doctor of Philosophy to the University of Cambridge, Gonville & Caius College.

DOI: 10.48456/tr-9


The CAP research project was set up in 1969 to investigate memory protection by designing and building a computer with hardware support for a very detailed protection system based on the use of capabilities. The computer has been built and an operating system written which exploits its protection facilities. It is time, therefore, to assess how successful the project has been. A necessary component of such an assessment is an evaluation of the CAP’s protection system and this thesis presents the results of the author’s research in this area.

Protection in computer systems is first introduced with a brief description of various models of protection systems and mechanisms for the provision of protection. There follows a description in some detail of the CAP computer and the CAP operating system with particular attention paid to those aspects of the design which are relevant to the research reported. A brief introduction to performance evaluation techniques is given followed by a discussion of performance evaluation on the CAP computer.

The need for measuring the benefits and costs of protection is discussed and there is a detailed critical description of the previous research in this area. A simple model of a protection system is presented as is a protection measure based on this model. There is then a discussion of how the services provided by modules in the system fit into the model and the protection measure. The application of the protection measure to the CAP operating system is described. The results led to suggestions for the improvement of the protection aspects of the operating system and these are discussed in detail. The implications of the results for operating system design in general are also discussed.

The experiements to investiage the cost of using the protection provided on the CAP are described next. Some performance evaluation work was done in connection with the protection cost experiments and this too is discussed.

Full text

PDF (7.1 MB)

BibTeX record

  author =	 {Cook, Douglas John},
  title = 	 {{Evaluation of a protection system}},
  url = 	 {},
  institution =  {University of Cambridge, Computer Laboratory},
  doi = 	 {10.48456/tr-9},
  number = 	 {UCAM-CL-TR-9}