An Operating system is the most important system software. It is a set of programs that control and supervise the hardware of a computer and also provide services to application software, programmers and users. It manages all hardware and software, input, output and processing activities within the computer system, the flow of information to and from the processor, sets priorities for handling different tasks, and so on. Without operating system a computer cannot do anything useful. When a computer is switched on, the operating system is the first program that is loaded onto Software Application Software System Software Operating System Language Translators Utility Software General Purpose Customized Software Compiler Assembler Interpreter its memory. A user cannot communicate directly with the computer hardware, so the operating system acts as an interface between the user and the computer hardware.
Some of the popular operating systems used in personal computers are DOS, Windows, Unix, Linux, Solaris, etc.
An operating system can be a Single User or a Multiuser operating system. A single user operating system allows only one user to work at any time but a multiuser operating system allows two or more users to use a powerful computer at the same time. For example, Windows 7 is a single user operating system while Linux is a multiuser operating system.