A graphical user interface (GUI) is a human-computer interface (i.e., a way for humans to interact with computers) that uses windows, icons and menus and which can be manipulated by a mouse (and often to a limited extent by a keyboard as well).

GUIs stand in sharp contrast to command line interfaces (CLIs), which use only text and are accessed solely by a keyboard. The most familiar example of a CLI to many people is MS-DOS. Another example is Linux when it is used in console mode (i.e., the entire screen shows text only).

The origin of the GUI can be traced back to Vannevar Bush, a scientist and futurist who worked at the Massachusetts Institute of Technology (MIT) during World War II. In his now classic 1945 magazine article As We May Think, Bush proposed an information administration tool, the Memex, that would allow data to be stored on microfilm and made easily accessible, linkable with hyperlinks and programmable. In 1963 Ivan Sutherland, a graduate student at MIT, developed a program for his Ph.D. dissertation called Sketchpad, which allowed the direct manipulation of graphic objects on a CRT screen using a light pen. His concept included the capability to zoom in and out on the display, the provision of memory for storing objects and the ability to draw precision lines and corners on the screen.

A window is a (usually) rectangular portion of the monitor screen that can display its contents (e.g., a program, icons, a text file or an image) seemingly independently of the rest of the display screen. A major feature is the ability for multiple windows to be open simultaneously. Each window can display a different application, or each can display different files (e.g., text, image or spreadsheet files) that have been opened or created with a single application.

A major advantage of GUIs is that they make computer operation more intuitive, and thus easier to learn and use. Adding to this intuitiveness of operation is the fact that GUIs generally provide users with immediate, visual feedback about the effect of each action. In addition, GUIs allow users to take full advantage of the powerful multitasking (the ability for multiple programs and/or multiple instances of single programs to run simultaneously) capabilities of modern operating systems by allowing such multiple programs and/or instances to be displayed simultaneously.

An operating system or OS, is a software program that enables the computer hardware to communicate and operate with the computer software. Without a computer operating system, a computer and software programs would be useless. An operating system is a program designed to run other programs on a computer. A computer’s operating system is its most important program. It is considered the backbone of a computer, managing both software and hardware resources.

Multi-user : Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users. Multiprocessing : Supports running a program on more than one CPU. Multithreading : Allows different parts of a single program to run concurrently. Real time: Responds to input instantly. General- purpose operating systems, such as DOS and UNIX, are not real-time.

When a single program is allowed to run at a time, the system is grouped under a single-tasking system, while in case the operating system allows the execution of multiple tasks at one time, it is classified as a multi-tasking operating system.

A real-time operating system is a multitasking operating system that aims at executing real-time applications. Real-time operating systems often use specialized scheduling algorithms so that they can achieve a deterministic nature of behavior. The main objective of real-time operating systems is their quick and predictable response to events.

A multi-user operating system allows multiple users to access a computer system concurrently. Time-sharing system can be classified as multi-user systems as they enable a multiple user access to a computer through the sharing of time. Single-user operating systems, as opposed to a multi-user operating system, are usable by a single user at a time. Being able to have multiple accounts on a Windows operating system does not make it a multi-user system.

Multi-user - A multi-user operating system allows for multiple users to use the same computer at the same time and different times. See the multi-user definition for a complete definition for a complete definition. Below are some examples of multi-user operating systems. Linux Unix Windows 2000 Multiprocessing - An operating system capable of supporting and utilizing more than one computer processor. Below are some examples of multiprocessing operating systems. Linux Unix Windows 2000

Multitasking - An operating system that is capable of allowing multiple software processes to run at the same time. Below are some examples of multitasking operating systems. Unix Windows 2000 Multithreading - Operating systems that allow different parts of a software program to run concurrently. Operating systems that would fall into this category are: Linux Unix Windows 2000

Thank You.. Chhavi Mahajan