Privileged processor modes
Most operating systems running on 32-bit and 64-bit processors control access to system resources using the concept of privilege levels. The primary reasons for managing access in this manner are to enhance system stability, prevent unauthorized access to system hardware, and prevent unauthorized access to data.
Privileged execution improves system stability by ensuring only trusted code is allowed to execute instructions with unrestricted access to resources such as processor configuration registers and I/O devices. The operating system kernel and related modules, including device drivers, require privileged access to perform their functions. Because any crash of a kernel process or a device driver is likely to halt the entire system immediately, these software components generally undergo a careful design process and rigorous testing before being released for general use.
Running the operating system in a privileged context prevents unauthorized applications...
