3 a Explain implicit and explicit priority scheduling withou

3. (a) Explain implicit and explicit priority scheduling without preemption and preemption. (b) Describe and explain an example application. (c) Which one use more context switches? Why?

Solution

(a) Priority scheduling always uses the process with highest prority and executes it. Nonpreemptive prority scheduling only selects a new process if the current process is finished completely. In preemptive priority scheduling while executing a process if a new process arrives with a higher priority the process is immediately switched and the higher prority process is executed.

Im explicit scheduling the task has to explicity call the scheduler to make the switch happen, where as this is not the case in implicit scheduling.

(b) Lets say we have processes P1 with priority 3 and P2 with priority 1, now the process P1 is executed. Now while P1 is being executed if a new process P3 arrives with priority 5, in non preemptive scheduling P3 has to wait until P1 is completed. In preemptive scheduling P1 is immediately switched with P3 and P3 starts executing.

(c) There will be more switches in  preemptive scheduling, as a switch happens immediately if a new process with higher priority arrives. This is not the case in non preemptive scheduling.