Of course, there does not have to be, but if there would then it would be very useful. Think MS-DOS 4.0 multitasking: <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;MS-DOS_4.0_(multitasking)" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;MS-DOS_4.0_(multitasking)</a><p>One process can have a preemptive multitasking. Even one process can make a very good use of a scheduler.