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. 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. The choice of operating system, therefore, determines to a great extent the applications that can run on it.
Users normally interact with the operating system through a set of commands.
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 users to enter commands by pointing and clicking at objects that appear on the screen. The WebServer Compare databank indicates the operating system required on the hardware system before the HTTP server can be installed. Most of the servers in the database are HTTP-based, and are designed for serving HTML pages across the Web. A few are designed for specialized environments, such as serving Java applications on embedded systems.