An operating system is software that manages all of the hardware resources associated with a computer (a desktop, a laptop...). To put it simply, the operating system manages the communication between your software and your hardware. Without the operating system (OS), the software wouldn't function.

Operating System

An operating system can be thought of as software that provides services that can be used for developing applications where multiple pieces of work (tasks) have to be worked on concurrently. At the center of an operating system is the scheduler, whose job is to decide which task is to run next.

In a cooperative multitasking operating system, a task runs till it decides to suspend what it is doing and transfer control to the scheduler, which will determine which task to run next.

In a preemptive multitasking operating system, a task can be preempted by the operating system at any point. Preemption may occur because a higher priority task is ready to run, or because the running task needs to access a resource that is currently not available because it is being used by another task.

The concept of Real Time refers to how long it takes the system to respond to some event, such as a button press, or arrival of data at a communications peripheral, or completion of an ADC (Analog to Digital) conversion. A distinction is often made between hard and soft real-time systems. In a hard real-time system, it is an error if the time taken for a response exceeds some specified duration. In a soft real-time system, the response time is interpreted in a statistical sense in which most of the time the required time-to-completion limits are met, but, occasionally, they are not.