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Chapter 6 Protection, Protection: All resources must be protected from interference. This includes protection from access by malicious code, but it also includes proction from faults and other processes that may be running on the same computer. Protection might also prevent the bypassing of required activities such as login authentication and authorization. Kernels and Protection Most processors have a hardware mode register that permits privileged instructions to be strictly controlled. Generally, there is a supervisor mode for privileged instructions and a user mode for unprivileged instructions. Separate address spaces are allocated, and only the privileged kernel can access the privileged spaces. Usually a system call trap is required to access privileged instructions from user space., Protection: All resources must be protected from interference. This includes protection from access by malicious code, but it also includes proction from faults and other processes that may be running on the same computer. Protection might also prevent the bypassing of required activities such as login authentication and authorization. Protection Overhead Protection comes at a price, includeing the processor cycles to switch between address spaces, the supervision and protection of system call traps, and the establishment, authentication and authorization of privileged users and processes. Since all overhead consumes expensive resources, it is always a key concern of IT managers.