Definition of:operating system
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.


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 operations were performed by typing in commands. Not extinct today, a command-line interface is included in all major operating systems, and technical operations are commonly executed from the command line by programmers and administrators.


Job Management
Job management controls the time and sequence that applications are run. Common in the mainframe and high-end server environment, IBM's job control language (JCL) was developed decades ago to schedule the daily work. The execution of short scripts at specific times throughout the day is common in Unix/Linux servers. 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 more often than not "task switching," which keeps applications open 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). When an application needs to retrieve or save data, it makes a call to the operating system's file system, which is in charge of opening, reading, writing and closing files. See API and file system.

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 each of the peripherals attached to the computer. When a different type of peripheral is attached, that device's driver must be added to the operating system if not previously installed. See driver.

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

In the 1950s, programmers wrote their own input/output routines to read and write magnetic tape. When magnetic disks came on the scene several years later, it became essential to have a separate program to manage them. In addition, running more than one application at a time (timesharing and multitasking) required a control program to keep track of everything.

Today, all computers from desktops to mainframes use an operating system. Even consumer electronics devices use an OS, whereas in the past, they used custom software that combined OS and application functionality. See Embedded Linux.

Common Operating Systems
The primary operating systems in use are Windows (7, Vista and XP), Macintosh OS X, the many versions of Linux and Unix, IBM i (stemming from the midrange AS/400) and z/OS (IBM mainframes). DOS is still used for some applications, and there are other special-purpose operating systems.

Smartphones and tablets use Apple's iOS, Google's Android, RIM's BlackBerry and QNX and Microsoft's Windows Phone.

Master Control
The operating system is the master control program in the computer.

Drivers and Peripherals

Operating System and Applications