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 operating system has even greater responsibilities and powers. The operating system is also responsible for security , ensuring that unauthorized users do not access the system. Allows two or more users to run programs at the same time.
Some operating systems permit hundreds or even thousands of concurrent users.
Supports running a program on more than one CPU . Allows more than one program to run concurrently. Responds to input instantly. Operating systems provide a software platform on top of which other programs, called application programs, can run. The application programs must be written to run on top of a particular operating system.