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    An operating system is a collection of programs that control a computer.

    This website will make use of CP/M (an early microcomputer OS) to illustrate the functions of an operating system. CP/M has the teaching advantage of being very small and simple (and therefore easier to understand) while also having at least rudimentary examples of most operating system functions (excluding graphic user interfaces).

    The file system and the shell program (especially graphic shell programs) are the primary ways that the typical computer user experiences a computer. Many people think of an operating system as just these two elements.

    The definition of an operating system is rather nebulous, especially at the border between software and hardware and the border between system and application software. A loose deifintion is an operating system is the collection of system software that controls the computer system.

    Computers are better at arcane details than humans. An operating system applies the power of computers to the job of managing a computer and its resources.

    An operating system is usually a collection of programs working together.

    An operating system can be viewed as a resource allocator. The operating system manages, keeps track of, and allocates both hardware and logical resources. Examples of allocation of hardware resources include allocation of CPU time, memory space, and input/output (I/O) devices. Examples of allocation of software resources include allocation of files, semaphores, and windows.

    An operating system can be viewed as a control program. The operating system controls the hardware and software running in a computer system. This view is reflected in the names CP/67 (Control Program for the IBM 360/67) and CP/M (Control program for Microcomputers).

    One of the most basic operations of an operating system is scheduling and control of processes or jobs (programs). This can include linking modules, loading programs, and running programs.

    In CP/M, a small program called the Monitor is loaded into memory when the computer is started and remains in memory until the computer is shutdown. The Monitor will load a new program at the user’s request and run the program by using the call (jump to subroutine) instruction.

    An operating system controls input and output devices, providing a common logical interface for use by application programs and mediating the allocation of these resources.

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    This web site handcrafted on Macintosh computers using Tom Bender’s Tex-Edit Plus and served using FreeBSD .

    Copyright © 2006 Milo

    Last Updated: November 19, 2006

    Created: July 14, 2006

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