说明：  根据单cpu系统任何一个时刻最多只能有一个进程处于cpu中处于执行状态，在进行进程调度时应按一定的原则实现进程的调度。 cpu优先调度是根据系统事先分配好的各优先级及编程者自己规定的进程优先级实现进程调度。优先级高的进程可以中断优先级低的进程而进入运行状态
(Single-cpu system according to any one moment only to have a process in the implementation in a cpu in the state, when conducting the process of scheduling a certain principle should be to achieve the process of scheduling. cpu priority scheduling is based on good distribution system in advance of the priority level and programmers of the process itself to achieve the process of scheduling priority. High-priority process can interrupt low-priority process to enter the running status)