operating system

operating system (OS)

Software that controls the operation of a computer, directs the input and output of data, keeps track of files, and controls the processing of computer programs. Its roles include managing the functioning of the computer hardware, running the applications programs, serving as an interface between the computer and the user, and allocating computer resources to various functions. When several jobs reside in the computer simultaneously and share resources (multitasking), the OS allocates fixed amounts of CPU time and memory in turn or allows one job to read data while another writes to a printer and still another performs computations. Through a process called time-sharing, a large computer can handle interaction with hundreds of users simultaneously, giving each the perception of being the sole user. Modern computer operating systems are becoming increasingly machine-independent, capable of running on any hardware platform; a widely used platform-independent operating system in use today on mainframe computers is UNIX. Most personal computers run on Microsoft's Windows operating system, which grew out of and eventually replaced MS-DOS. See also Linux.

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operating system

The computer's master control program. When the computer is turned on, a small "boot program" loads the operating system. Although additional system modules may be loaded as needed, the main part, known as the "kernel" resides in memory at all times.

The operating system (OS) sets the standards for all application programs that run in the computer. Applications "talk to" the operating system for all user interface and file management operations. Also called an "executive" or "supervisor," an operating system performs the following functions.

User Interface
All graphics based today, the user interface includes the windows, menus and method of interaction between the user and the computer. Prior to graphical user interfaces (GUIs), all operation of the computer was performed by typing in commands. Not at all extinct, a command-line interface is included in all major operating systems, and certain highly technial operations must be executed from the command line.

Operating systems may support optional interfaces. Although the overwhelming majority of people work with the default interface, different "shells" offer variations of appearance and functionality. See GUI, shell and skin.

Job Management
Job management controls the order and time in which applications are run and is more sophisticated in the mainframe environment where scheduling the daily work has always been routine. IBM's job control language (JCL) was developed decades ago for that purpose. In a desktop environment, batch files can be written to perform a sequence of operations that can be scheduled to start at a given time.

Task Management
Multitasking, which is the ability to simultaneously execute multiple programs, is available in all operating systems today. Critical in the mainframe and server environment, applications can be prioritized to run faster or slower depending on their purpose. In the desktop world, multitasking is necessary for keeping several applications open at the same time so users can bounce back and forth among them. See multitasking.

Data Management
Data management keeps track of the data on disk and other storage devices. The application program deals with data by file name and a particular location within the file. The operating system's file system knows where the data are physically stored (which sectors on disk) and interaction between the application and operating system is through the programming interface (API). Whenever an application needs to read or write data, it makes a call to the operating system (see API).

Device Management
Device management controls peripheral devices by sending them commands in their proprietary command language. The software routine that deals with each device is called a "driver," and the OS requires drivers for the peripherals attached to the computer. When a new peripheral is added, that device's driver is installed into the operating system. See driver.

Security
Operating systems provide password protection to keep unauthorized users out of the system. Some operating systems also maintain activity logs and accounting of the user's time for billing purposes. They also provide backup and recovery routines for starting over in the event of a system failure.

History
The earliest operating systems were developed in the late 1950s to manage tape storage, but programmers mostly wrote their own I/O routines. In the mid-1960s, operating systems became essential to manage disks, complex timesharing and multitasking systems.

Today, all multi-purpose computers from desktop to mainframe use an operating system. Consumer electronics devices increasingly use an OS, whereas in the past, they used custom software that provided both OS and application functionality (see embedded Linux).

Common Operating Systems
The primary operating systems in use are Windows (Windows 7, Vista, XP), Macintosh OS X, the many versions of Linux and Unix, i5/OS (IBM System i) and z/OS (IBM System z mainframes). DOS is still used for some applications, and there are many other special-purpose operating systems.

System and Application Software

This diagram shows how the major system software interacts with applications in memory. System software comprises the programs that support the running of applications (operating system, DBMS, TP monitor and access methods).

Drivers and Peripherals

This diagram shows the interaction between the operating system, the drivers and the peripheral devices.

Operating System and Application Software

This diagram shows the components of the operating system and typical application programs that run in a desktop computer.

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operating system

the set of software that controls the overall operation of a computer system, typically by performing such tasks as memory allocation, job scheduling, and input/output control

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operating system [′äp·ə‚rād·iŋ ‚sis·təm]

(computer science)

A set of programs and routines which guides a computer or network in the performance of its tasks, assists the programs (and programmers) with certain supporting functions, and increases the usefulness of the computer or network hardware.

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Operating system

The software component of a computer system that is responsible for the management and coordination of activities and the sharing of the resources of the computer. The operating system (OS) acts as a host for application programs that are run on the machine. As a host, one of the purposes of an operating system is to handle the details of the operation of the hardware. This relieves application programs from having to manage these details and makes it easier to write applications. Almost all computers, including hand-held computers, desktop computers, supercomputers, and even modern video game consoles, use an operating system of some type. See Computer systems architecture

Operating systems offer a number of services to application programs and users. Applications access these services through application programming interfaces (APIs) or system calls. By invoking these interfaces, the application can request a service from the operating system, pass parameters, and receive the results of the operation. Users may also interact with the operating system by typing commands or using a graphical user interface (GUI, commonly pronounced “gooey’’). For hand-held and desktop computers, the GUI is generally considered part of the operating system. For large multiuser systems, the GUI is generally implemented as an application program that runs outside the operating system. See Computer programming, Human-computer interaction

Modern operating systems provide the capability of running multiple application programs simultaneously, which is referred to as multiprogramming. Each program running is represented by a process in the operating system. The operating system provides an execution environment for each process by sharing the hardware resources so that each application does not need to be aware of the execution of other processes. The central processing unit (CPU) of the computer can be used by only one program at a time. The operating system can share the CPU among the processes by using a technique known as time slicing. In this manner, the processes take turns using the CPU. Single-user desktop personal computers (PCs) may simplify this further by granting the CPU to whichever application the user has currently selected and allowing the user to switch between applications at will.

The main memory of a computer (referred to as random access memory, or RAM) is a finite resource. The operating system is responsible for sharing the memory among the currently running processes. When a user initiates an application, the operating system decides where to place it in memory and may allocate additional memory to the application if it requests it. The operating system may use capabilities in the hardware to prevent one application from overwriting the memory of another. This provides security and prevents applications from interfering with one another. See Computer storage technology

The details of device management are left to the operating system. The operating system provides a set of APIs to the applications for accessing input/output (I/O) devices in a consistent and relatively simple manner regardless of the specifics of the underlying hardware. The operating system itself will generally use a software component called a device driver to control an I/O device. This allows the operating system to be upgraded to support new devices as they become available. In addition to a device driver for the network I/O device, the operating system includes software known as a network protocol and makes various network utilities available to the user. See Computer peripheral devices, Local-area networks, Wide-area networks

Operating systems provide security by preventing unauthorized access to the computer's resources. Many operating systems also prevent users of a computer from accidentally or intentionally interfering with each other. The security policies that an operating system enforces range from none in the case of a video game console, to simple password protection for hand-held and desktop computers, to very elaborate schemes for use in high-security environments. See Computer security

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(operating system)

operating system - (OS) The low-level software which handles the interface to peripheral hardware, schedules tasks, allocates storage, and presents a default interface to the user when no application program is running. The OS may be split into a kernel which is always present and various system programs which use facilities provided by the kernel to perform higher-level house-keeping tasks, often acting as servers in a client-server relationship. Some would include a graphical user interface and window system as part of the OS, others would not. The operating system loader, BIOS, or other firmware required at boot time or when installing the operating system would generally not be considered part of the operating system, though this distinction is unclear in the case of a rommable operating system such as RISC OS. The facilities an operating system provides and its general design philosophy exert an extremely strong influence on programming style and on the technical cultures that grow up around the machines on which it runs. Example operating systems include 386BSD, AIX, AOS, Amoeba, Angel, Artemis microkernel, BeOS, Brazil, COS, CP/M, CTSS, Chorus, DACNOS, DOSEXEC 2, GCOS, GEORGE 3, GEOS, ITS, KAOS, Linux, LynxOS, MPV, MS-DOS, MVS, Mach, Macintosh operating system, Microsoft Windows, MINIX, Multics, Multipop-68, Novell NetWare, OS-9, OS/2, Pick, Plan 9, QNX, RISC OS, STING, System V, System/360, TOPS-10, TOPS-20, TRUSIX, TWENEX, TYMCOM-X, Thoth, Unix, VM/CMS, VMS, VRTX, VSTa, VxWorks, WAITS. FAQ. Usenet newsgroup: news:comp.os.research.