Preemptive multitasking is a task used by the OS to decide for how long a task should be executed before allowing another task to use the OS.

How preemptive multitasking is used in a computer system?

In simple terms: Preemptive multitasking involves the use of an interrupt mechanism which suspends the currently executing process and invokes a scheduler to determine which process should execute next. Therefore, all processes will get some amount of CPU time at any given time.

Where is a multitasking operating system used?

Microsoft Windows 2000, IBM's OS/390, and Linux are examples of operating systems that can do multitasking (almost all of today's operating systems can). When you open your Web browser and then open Word at the same time, you are causing the operating system to do multitasking.