operating system (OS)

Master control program (such as DOS, Linux, MacOS, Solaris, Unix, and Windows) that automatically runs first when a computer is switched on, and remains in the background until the computer is turned off. It commonly comes preinstalled (on the boot section of the computer's main hard disk) and is usually the most complex and largest program to be used by the computer. A computer user is typically more affected by the capabilities and whims of the OS than by those of the hardware. Main services provided by an OS include (1) user-interface, (2) carrying out commands of the user and the application programs, (3) supervising installation and running of other programs and hardware, (4) controlling the input-output functions, (5) allocating system resources such as memory, processor time, disk space, and peripheral devices to regulate the flow of work within the computer, (6) handling file and directory management, and (7) providing file-sharing and networking functions.