Лекция: The Definition of the OS

An operating system (commonly abbreviated as OS and O/S) is the software component of a computer system that is responsible for the management and coordination of activities and the sharing of the resources of the computer. It is the most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers. For large systems, the OS has even greater responsibilities and powers. It is like a traffic cop (гаишник) – it makes sure that different programs and users running at the same time do not interfere with each other. The OS is also responsible for security, ensuring that unauthorized users do not access the system. Almost all computers, including hand-held computers, desktop computers, supercomputers and even modern video game consoles, use an operating system of some type.

Operating systems can be classified as follows:

· Multi-user (многопользовательские): allow two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users.

· Multi-processing: support running a program on more than one CPU.

· Multi-tasking: allow more than one program to run concurrently (одновременно).

· Real time: respond to input instantly (реагируют на вход мгновенно).

Operating systems provide a software platform on top of which other programs, called application programs (прикладные), can run. The application programs must be written to run a particular operating system. Your choice of operating system, therefore, determines to a great extent the applications you can run. For PCs, the most popular operating systems are Windows, OS/2, Linux.

As a user, you normally interact with the OS through a set of commands. For example, the DOS operating system contains commands such as COPY and RENAME for copying files and changing the names of files, respectively. The commands are accepted and executed by a part of the operating system called the command processor or command line interpreter. Graphical user interfaces allow you to enter commands by pointing and clicking at objects that appear on the screen.