Free What the OS does lessonsWhat the OS does · Stage 0 · The operating system's job · Step 2
Kernel mode and user mode
Why the CPU has two privilege levels, and what stops a program from taking over the machine. About 12 minutes.
Why can't a user program simply switch the CPU into kernel mode itself?
- AChanging the mode is itself a privileged operation, enforced by the hardware
- BThe OS checks every instruction in software before it runs
- CIt would need the administrator's password
Show the answer
Changing the mode is itself a privileged operation, enforced by the hardware. User-mode code is physically not allowed to run it.
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