Protection
Protect user processes from each other
- Disallow an unauthorized process to access (read, write, execute) part of the addressing space of another process
Disallow the use of some instructions by user processes
- E.g., disallow process A to change the access rights to process B
Leads to
- Kernel mode (operating system) vs. user mode
- Only kernel mode can use some privileged instructions (e.g., disabling interrupts, I/O functions)
- Providing system calls whereby CPU can switch between user and kernel mode