Operating System

An operating system (OS) is a collection of software that managescomputer hardware resources and provides common services forcomputer programs. The operating system is a vital component of thesystem software in a computer system. Application programs usually require an operating system to function.

Time-sharing operating systems schedule tasks for efficient use of the system and may also include accounting for cost allocation of processor time, mass storage, printing, and other resources.

Examples of popular modern operating systems include Android, BSD,iOS, Linux, Mac OS X, Microsoft Windows,Windows Phone, and IBM z/OS. All these, except Windows and z/OS, share roots in UNIX.For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware,although the application code is usually 

executed directly by the hardware and will frequently make a system call to an OS function or be interrupted by it. Operating systems can be found on almost any device that contains a computer—from cellular phones and video game consoles to supercomputers and web servers.