Protection in an information processing utility

Another example of the application of the criteria can be found by asking whether a multiprogrammed system's main memory protection should apply to reading as well as writing. That is, should a user's virtual processing unit be able to read another user's virtual main memory? Applying the present criteria, the designer has the following choice: either he provides each user with means for recording and specifying the values read from other users' virtual memories, or he prohibits the reading of other users' virtual memories.