operating system - technical definition

The computer's master control program. When the computer is turned on, a small "boot program" loads the operating system. Although additional 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 you and the computer. Prior to graphical user interfaces (GUIs), all operation of the computer was performed by typing in commands. Not at all extinct, command-line interfaces are alive and well and provide an alternate way of running programs on all major operating systems.

Operating systems may support optional interfaces, both graphical and command line. Although the overwhelming majority of people work with the default interfaces, different "shells" offer variations of appearance and functionality.

Job Management
Job management controls the order and time in which programs 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. 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 you can bounce back and forth among them. See multitasking.

Data Management
Data management keeps track of the data on disk, tape and optical 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 that data are physically stored (which sectors on disk) and interaction between the application and operating system is through the programming interface. 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 own proprietary language. The software routine that knows how to deal 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 98, XP, Vista), Macintosh OS X, the many versions of Linux and Unix, i5/OS (IBM iSeries) and z/OS (IBM zSeries mainframes). DOS is still used for some applications, and there are many other special-purpose operating systems.