Explain non-pre-emptive algorithms?  

Non preemptive algorithms: In this algorithm a job is provided to CPU for execution as long as the job is non-completed the CPU cannot be provided to other processes.

There are three kinds of non preemptive algorithms.

(i) First-come-first-serve (FCFS): This is simplest CPU scheduling algorithm. Along with this scheme, the process which requests the CPU at first is provided to the CPU at first. The implementation of First Come First Serve is easily managed through with a FIFO queue.

(ii) Shortest-job-first (SJF): It is also termed as SPN (shortest process next). In this algorithm the burst times of all the jobs that are waiting in the queue are compared. The job that is containing the least CPU execution time will be provided to the processor at first. In such turnaround time and waiting times are least. It also suffers along with starvation. Indefinite waiting time is termed as starvation. This is complex than FCFS.

(iii) Priority: In this method every job is related with CPU execution time, arrival time and the priority. Here the job that is containing the higher priority will be specified to the execution at first. It also suffers with starvation. And through using aging technique starvation effect may be decreased.