三段
The operating system defines our computing experience. It's the first
software we see when we turn on the computer,and the last software we
see whenthe computer is turned off. It's the software that enables all
the programs we use. The operatings system organizes and controls the
hardware on our desks and in our hands,yet most users can't say with
any certainty precisely what it is that the operating system does.
It's important to realize that not all computers have operating systems. The computer that controls the microwave oven in your kitchen ,for example,does't need an operating system.It has one set of
relatively simple tasks to perform ,very simple input and output methods(a keypad and an LCD screen),and simple,never-changing hardware to control. For a computer like this, an operating system would be unnecessary baggage,adding complexity where none is required. Instead, the computer is a microwave oven simply runs a single program all the time.
As for computer systems that go beyond the complexity of the microwave ,however,an operating system can be the key to greater operating efficiency and easier application development.All desktop computers have operating systems.The most common are the Wingows family of operating systems,the UNIX family of operating systems available for
special-purpose applications,including specializations for mainframes,
robotics,manufacturing,real-time control systems and so on.