在CPU调度中，我们有两种调度方式，让我们来看看它们：
抢占式调度：
在这种情况下，当高优先级进程进入就绪状态时，调度器可以随时抢占低优先级正在运行的进程。当调度来自以下任一情况时，它是抢占式调度——
- 当进程从运行状态切换到就绪状态时(例如，发生中断时)。
- 当进程从等待状态切换到就绪状态时(例如，在完成 I/)时)。
非抢占式调度：
在这种情况下，一旦一个进程进入运行状态，它就不能被抢占，直到它完成它的分配时间。当调度仅在以下情况下发生时，我们说调度方案是非抢占式或合作式的。 ——
- 当进程从运行状态切换到等待状态时(例如，作为 I/O 请求或调用 wait() 以终止子进程的结果)。
- 当一个进程终止时。
让我们看看抢占式调度和非抢占式调度之间的区别：
| S.No. | Preemptive Scheduling | Non-Preemptive Scheduling | ||||||
|---|---|---|---|---|---|---|---|---|
| 1. | The CPU is allocated to the processes for a certain amount of time. | The CPU is allocated to the process till it ends it’s execution or switches to waiting state. | ||||||
| 2. | The executing process here is interrupted in the middle of execution. | The executing process here is not interrupted in the middle of execution. | ||||||
| 3. | It usually switches the process from ready state to running state, vise-versa, and maintains the ready queue. | It does not switch the process from running state to ready state. | ||||||
| 4. | Here, if a process with high priority frequently arrives in the ready queue then the process with low priority has to wait for long, and it may have to starve. | Here, if CPU is allocated to the process with larger burst time then the processes with small burst time may have to starve. | 5. | It is quite flexible because the critical processes are allowed to access CPU as they arrive into the ready queue, no matter what process is executing currently. | It is rigid as even if a critical process enters the ready queue the process running CPU is not disturbed. | 6. | This is cost associative as it has to maintain the integrity of shared data. | This is not cost associative. |
抢占式调度优于非抢占式调度，反之亦然不能肯定。这取决于调度如何最小化进程的平均等待时间并最大化 CPU 利用率。