1.BOOTING
                     (also known as booting up) is a bootstrapping process that starts operating systems when the user turns on a computer system. A boot sequence is the initial set of operations that the computer performs when power is switched on. The boot loader typically loads the main operating system for the computer.
2.GUI
                     a type of user interface that allows users to interact with electronic devices with images rather than text commands
3.LINUX
                     is a computer operating system which is based on free and open source software. Although many different varieties of Linux exist, all are Unix-like and based on the Linux kernel, an operating system kernel created in 1992.

4.MACINTOSH OS
                       Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. (formerly Apple Computer, Inc.) for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface. The original form of what Apple would later name the "Mac OS" was the integral and unnamed system software first introduced in 1984 with the original Macintosh, usually referred to simply as the System software.                    
5.MS-DOS
                        short for Microsoft Disk Operating System) is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating systems offering a graphical user interface (GUI), in particular by various generations of the Microsoft Windows operating system. 


 6.MULTITASKING
Multitasking may refer to any of the following:

• Computer multitasking - the apparent simultaneous performance of two or more tasks by a computer's central processing unit
• Media multitasking could involve using a computer, mp3, or any other form of media in conjunction with one another.
• Human multitasking - The ability of a person to perform more than one task at the same time.

7.NOS 

8.OS  
              software, consisting of programs and data, that runs on computers, manages computer hardware resources, and provides common services for execution of various application software. The operating system is the most important type of system software in a computer system. Without an operating system, a user cannot run an application program on their computer, unless the application program is self booting.

9.SYSTEM SOFTWARE
                 is computer software designed to operate the computer hardware and to provide a platform for running application software.

10.APPLICATION SOFTWARE                                                                                                                                    computer software designed to help the user to perform specific tasks. Examples include enterprise software, accounting software, office suites, graphics software and media players. Many application programs deal principally with documents. Apps may be bundled with the computer and its system software, or may be published separately. Some users are satisfied with the bundled apps and need never install one.

11.UNIX

                 is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy and Joe Ossanna. The Unix operating system was first developed in assembly language, but by 1973 had been almost entirely recoded in C, greatly facilitating its further development and porting to other hardware. Today's Unix systems are split into various branches, developed over time by AT&T as well as various commercial vendors and non-profit organizations. The second edition of Unix was released on December 6th, 1972.
12.UTILITY PROGRAMS
                  A program that supports using the computer, an application or a development environment. Also called "utilities," utility software is programmed like any other software, except that it plays a supporting role. Usually relatively small programs, they typically perform a limited number of tasks.

13.WINDOWS 
                   "Windows" redirects here. For the part of a building, see Window. For other uses, see Windows (disambiguation).  
14.WINDOWS CE
                     Microsoft Windows CE (now officially known as Windows Embedded Compact and previously also known as Windows Embedded CE , and sometimes abbreviated WinCE) is an operating system developed by Microsoft for embedded systems. Windows CE is a distinct operating system and kernel, rather than a trimmed-down version of desktop Windows.It is not to be confused with Windows Embedded Standard which is an NT-based componentized version of desktop Microsoft Windows. 15.WINDOWS MOBILE
                      Windows Mobile is a mobile operating system developed by Microsoft that was used in smartphones and mobile devices, but by 2011 was rarely supplied on new phones. The last version is "Windows Mobile 6.5.5"; it is superseded by Windows Phone 7, which does not run Windows Mobile software. Unlike operating systems for desktop computers, it is usually not possible to upgrade the operating system on a Microsoft based mobile phone via official and legal means, even by a later release of the same basic operating system let alone a different one; hardware replacement is the only way for less popular and older devices.