What is the instruction:
Instruction: The most basic of commands executed by CPU can recognize and
understand: let the CPU work
Issues: CPU know how it is a privileged instruction? 
Kernel mode: ROOT account the environment,
for the state: the ordinary user account the environment in which
different programs have different command authority, there is also a distinction
ROOT account can execute non-privileged instruction, privileged instructions can be executed
ordinary account can only execute common commands
function kernel program mainly implemented:
Since the internal allocation of each operating system kernel are not the same,
so we put some necessary and hardware deal called microkernel
and the entire kernel called kernel large
