The operating system is the large, relatively complex, low-level piece of software that interfaces your hardware to the software applications you want to run. The operating system you use is closely related to the file system that manages your hard disk data. The reason is a simple one: different operating systems use different file systems. Some are designed specifically to work with more than one, for compatibility reasons; others work only with their own file system.

Microsoft DOS (Disk Operating System) is a command line user interface. MS-DOS 1.0 was released in 1981 for IBM computers and the latest version of MS-DOS is MS-DOS 6.22, which was released in 1994. While MS-DOS is not commonly used by itself today, it still can be accessed from every version of Microsoft Windows by clicking Start / Run and typing "command" or by typing "CMD" in Windows NT, Windows 2000 or Windows XP.

The software component can further be divided into: application software and operating system software.

Operating System Role
* The operating system is responsible for hardware management. The operating system directly controls both system hardware and peripherals.
* The operating system provides an environment for the execution of application programs.
For example, a Windows 2000 system can also run most applications written for Windows 3.x and MS-DOS by emulating those operating systems.

* The end-user interface is another operating system responsibility. (The desktop is the end-user interface and working area on a Windows family operating system).
* Earlier operating systems were limited to a command line interface. All interaction between the end user and the computer was through textual commands.
* The current standard is a graphic user interface (GUI) environment based on a desktop metaphor.

Operating System Categories
The two general operating system categories are network operating systems and end-user operating systems.

* Network operating systems are also called server operating systems. A network operating system provides the software needed for a PC to manage, control and support a local or wide area network environment.

* End-user operating systems are also known as client operating systems. The term client comes from the fact that end-user operating systems can access resources provided by network services as a network client.

Operating System Components
An operating system is composed of several files, each performing specific operating tasks and providing operating system functionality.

For example, system utilities are commonly documented as part of the operating system.

System Kernel
The system kernel sits at the core of the operating system. All low-level operating system functions are implemented at the kernel level. The kernel of most modern operating systems is composed of several files that work together to control and manage system hardware.

In simple terms, kernel-level activities are operating system activities that deal directly with system hardware. User-level activities, as the name implies, deal with the user interface and applications.

Device Drivers
Device drivers are specialized programs that allow the operating system to communicate with and control hardware devices such as printers, video adapters and network adapters.

Operating system service packs, which contain operating system updates and corrections, often include updated device drivers.

User Interface
The user interface gives the user a way to communicate with the operating system and through the operating system with the system hardware.

Windows family operating systems default to using a GUI interface. They also allow you to launch the operating system with a command line interface.

Application Environment
One of the most important functions of an operating system is providing an environment for applications. Most operating systems can often support applications written for other operating systems through emulation.

Emulation, in short, provides an environment that looks and acts like another operating system.

Applications can use features built into the operating system through application programming interface (API) files. APIs keep a programmer from having to "reinvent the wheel" by re-creating low-level routines that emulate functionality already built into the operating system.

Most current operating systems will not let applications directly access or control system hardware. The applications must make requests to the operating system.

One reason you should know that fact is that this limitation will cause some older applications, especially troubleshooting applications and utilities, to fail.

Common Operating Systems

MS-DOS, WINDOWS 3.x, WINDOWS 9.x, WINDOWS NT, WINDOWS 2000
OS/2
UNIX
LINUX
NETWARE

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