II. Reading Read the text and be ready to answer the following questions:

• What is an operating system?

• How does it work?

• What operating systems are there?

Operating System

An operating system is an important part of a computer system. A computer system is built from three general components: the hardware, the operating system, and the applications. The hardware includes pieces such as a central processing unit (CPU), a keyboard, a hard drive and a printer. You can think of these as the parts you are able to touch physically. Applications are why you use computers; they use the rest of the system to perform the desired task (for example, play a game, edit a memo, send electronic mail). The operating system is the component that on one side manages and controls the hardware and on the other manages the applications.

When you purchase a computer system, you must have at least hardware and an operating system. The hardware you purchase is able to use (or run) one or more different operating systems. You can purchase a computer package, which includes the hardware, the operating system, and possibly one or more applications. The operating system is necessary in order to manage the hardware and applications.

When you turn on your computer, the operating system performs a series of tasks, presented here in chronological order.

One of the first things you do, after successfully plugging together cables and components, is turn on your computer. The operating system takes care of all the starting functions that must occur to get your computer to a usable state. Various pieces of hardware need to be initialized. After the start-up procedure is complete, the operating system awaits further instructions. If you shut down the computer, the operating system also has a procedure that makes sure all the hardware is shut down correctly. Before turning your computer of again, you might want to do something useful, which means that one or more applications are executed.

After the operating system completes hardware initialization, you can execute an application. The executing application is called a process. It is the operating system’s job to manage execution of the application. When you execute a program, the operating system creates a new process. Many processes can exist simultaneously. This process is referred to as multitasking. When you exit your program (or it finishes executing) the process terminates, and the operating system manages the termination by reclaiming any resources that were being used. Most applications perform some tasks between the time the process is created and the time it terminates. To perform these tasks, the program makes requests to the operating system, and the operating system responds to the requests and allocates necessary resources to the program. When an executing process needs to use some hardware, the operating system provides access for the process.

To perform its task, a process may need to access hardware resources. The process may need to read or write a file, send data to a network card (to communicate with another computer), or send data to a printer. The operating system provides such services for the process. This is referred to as resource allocation. A piece of hardware is a resource, and the operating system allocates available resources to the different processes that are running.

All computers do not use the same operating systems. It is therefore important to assess the operating system used on a particular model before initial commitment because some software is only designed to run under the control of specific operating systems. Some operating systems are adopted as ’’industry standards’’ and these are the ones which should be evaluated because they normally have a good software base. The reason for this is that software houses are willing to expand resources on the development of application packages for machines functioning under the control of an operating system which is widely used. The cost of software is likely to be lower in such circumstances as the development costs are spread over a greater number of users, both actual and potential.

Mainframe computers usually process several application programs concurrently, switching from one to the other, for the purpose of increasing processing productivity. This is known as multiprogramming, which requires a powerful operating system. An operating system is stored on disk and has to be booted into the internal memory (RAM) where it must reside through processing so that commands are instantly available. The operating system commands may exceed the internal memory capacity of the computer in which case only that potion of the operating system which is frequently used is retained internally, other modules being read in from disk as required.