What Is The Difference Between A Preemptive And Non-preemptive Scheduling'?

The difference between 'Preemptive' and 'Non-preemptive scheduling', is that Non-preemptive Scheduling occupies full control of the CPU whereas Preemptive Scheduling allows the computer's Operating System, (OS), control over the states of processes. It may help to understand a little about the different states of a computer process:

• Process States

There are five states which a process goes through during its cycle;

1. New - When a process is first activated or created such as when launching a software program (we'll keep to this example throughout this explanation).
2. Ready - When the program is ready to be assigned to the processor.
3. Running - When the program is being executed it is known as 'running'.
4. Waiting - The process here is dormant and waiting for communication from other processes.
5. Terminated - The term used for when the executed process has finished.

• Preemptive Scheduling

Preemptive Scheduling is when a computer process is interrupted and the CPU's power is given over to another process with a higher priority. This type of scheduling occurs when a process switches from running state to a ready state or from a waiting state to a ready state.

• Non-Preemptive Scheduling

Non-Preemptive Scheduling allows the process to run through to completion before moving onto the next task.

Here is an example of the former Preemptive Scheduling -  if you launch a software application such as a text editor, the OS will assign the task to the processor, and will allocate disk space, memory and other resources to the program; the text editor program is now in a running state. If you decide to launch a second application and a new process is generated, various necessary resources are assigned to the new program, and the text editor is kept in a waiting or ready state until the new process has been executed.

In Preemptive scheduling the process in forcibly sent to waiting state when a process with higher priority comes to cpu.
In non_preemptive scheduling the process at running state can not be forced to leave the cpu unless it completes.

NON-PREEMPTIVE  : It is the shedulling in which the process os the task on any processor is not terminated until it is completed
PREEMPTIVE  :the shedule for which the above is not the case