无论是在批处理系统还是分时系统中，用户进程数一般都多于处理机数、这将导致它们互相争夺处理机。另外，系统进程也同样需要使用处理机。这就要求进程调度程序按一定的策略，动态地把处理机分配给处于就绪队列中的某一个进程，以使之执行。　-Whether in a batch system or time-sharing system, the process of the number of users are generally more than a few processors, which will lead them to each other for processing. In addition, the system process also need to use the processor. This requires the process of scheduling procedures in accordance with a certain degree of strategy, dynamically allocated to the processor in a queue in place a process to enable the implementation.