CPU Protection Mechanism

If the program can directly interact with the kernel, the operating system will become unstable. Therefore, there is a mechanism that separates the kernel from the program.

Generally, the CPU has a layer-4 protection mechanism.

0th ring, privileged level. Only the kernel can run at level 0th,

The outermost ring. Other programs run.

So the same is true for memory.

650) This. width = 650; "src =" http://s3.51cto.com/wyfs02/M00/46/F4/wKioL1P1XpDgpXH-AACpiysyVQk697.jpg "Title =" qq201408211020.8.png "alt =" wKioL1P1XpDgpXH-AACpiysyVQk697.jpg "/>