We have already alluded several times to the fact that processes within a computing system must be protected from each other’s activities. We have introduced mechanisms at various points in our paper operating system which ensure that the memory, files, and resources belonging to a process cannot be accessed by another process except in a controlled manner. The mechanisms have been distributed throughout the system in such places as the memory addressing hardware, file directories, and resource allocation procedures, and have functioned more or less independently of each other. In this chapter we take a closer look at the subject of protection as a whole and indicate how it is possible to implement protection mechanisms on a unified system-wide basis.
KeywordsProtection Scheme Capability Register Address Space Ring Number Code Segment
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