What are the restrictions implied on API functions? - Windows Programming

What are the restrictions implied on API functions?

- The use of API function is to provide easy to use interface and have functions that reads the processes and memory.

- API function can read the memory region and can be used by anyone without any restrictions.

- The restrictions implied on the functions are as follows:

- Windows API functions call different API that is known as Native API. This allows the easy interaction with the kernel, but at this time the CPU switches to the kernel mode.

- The special instruction for the system calls like sysenter and sysexit allow the CPU to switch to the ring 0, which in turn execute the handler provided by the operating system.