16. What is an operating system, how does it act, what are common contemporary operating systems? What is system software, application software, utility software?

An operating system (OS or O/S) is an interface (connection) between hardware and user - it determines how the user interacts with the computer; it is responsible for the management and coordination of activities and the sharing of the resources of the computer. The operating system acts as a host for applications that are run on the machine, handling the details of the operation of the hardware. The purpose of an operating system is to organize and control hardware and software so that the device it lives in behaves in a flexible but predictable way. The operating system is started automatically when a computer is switched on, it is the first thing loaded onto the computer - without the operating system, a computer is useless.

Common contemporary operating systems include Microsoft Windows (designed by Microsoft and used on most PCs), Mac OS (created by Apple and used on Macintosh computers). Microsoft Windows has a significant majority of market share in the desktop and notebook computer markets, while servers generally run on Unix or Unix-like systems (found on mainframes and workstations in corporate installations, as it supports multi-users).

System software helps run the computer hardware and computer system. It includes operating systems, device drivers, diagnostic tools, servers, windowing systems, utilities, language translator, data communication programs, data management programs and more. The purpose of systems software is to insulate the applications programmer as much as possible from the details of the particular computer complex being used, especially memory and other hardware features, and such accessory devices as communications, printers, readers, displays, keyboards, etc.

Application software is any tool that functions and is operated by means of a computer, with the purpose of supporting or improving the software user's work. In this context the term application refers to both the application software and its implementation.

Utility software (also known as service program, service routine, tool, utility routine or system utilities) is computer software designed to help manage and tune the computer hardware, operating system or application software. Utility software has long been integrated into most major operating systems. Utilities are often desk accessories that can be called up while you're working in another application. They can also be system extensions which are activated when you turn on the computer, control devices which you adjust in the control panel, or even stand-alone programs that run when you need them.

Utilities are available for back-up, file search, virus protection, disaster recovery, and so on. Accessibility program makes a PC easier for disabled users to use. Anti-virus utilities scan for computer viruses.

Disk cleaners Disk compression File managers. Launcher applications Media player