Each executing program is a task under control of the operating system. If an operating system can execute multiple tasks in this manner it is said to be multitasking.
The use of a multitasking operating system can simplify the design of what would otherwise be a complex software
application:
Multitasking Vs Concurrency
A conventional processor can only execute a single task at a time - but by rapidly switching between tasks a multitasking operating system can make it appear as if each task is executing concurrently. This is depicted by the diagram below which shows the execution pattern of three tasks with respect to time. The task names are color coded and written down the left hand. Time moves from left to right, with the colored lines showing which task is executing at any particular time. The upper diagram demonstrates the perceived concurrent execution pattern, and the lower the actual multitasking execution pattern.