DIFFERENCES BETWEEN PREEMPTIVE AND NON-PREEMPTIVE SCHEDULING

1.) In preemptive scheduling we prempt the currently executing process, 
In non preemptive scheduling we allow the current process to finish its CPU burst time.

2.) In preemptive scheduling the process is forcibly sent to waiting state when a process with higher priority comes to CPU, In non preeemptive scheduling the process at running state can not be forced to leave the CPU until it completes

Non-Preemptive: Non-preemptive algorithms are designed so that once a process enters the running state(is allowed a process), it is not removed from the processor until it has completed its service time ( or it explicitly yields the processor). context_switch() is called only when the process terminates or blocks.

Preemptive: Preemptive algorithms are driven by the notion of prioritized computation. The process with the highest priority should always be the one currently using the processor. If a process is currently using the processor and a new process with a higher priority enters the ready list, the process on the processor should be removed and returned to the ready list ,until it is once again the highest-priority process in the system