Since the introduction of personal computers in the early 1980s, there has been a continuing effort to make them easier and more intuitive to use.  Early computer operating systems were entirely text-based and required a user to type in the individual commands that made the computer perform such tasks as opening a document, storing a document, deleting a document, etc.  The text-based operating systems required a user to have a high degree of computer literacy in order to use the system properly.  The operating system commands were generally non-intuitive and the systems were unforgiving in that each command had to be typed according to the proper syntax without a mistake before the command would be executed by the computer. 
The popular systems produced in the second generation of personal computer operating systems were graphics based.  For example, the Apple MacIntosh. TM.  and the Microsoft Windows. TM.  systems were a vast improvement over previous text-based operating systems.  In a typical graphics-based operating system, a number of icons, i.e., graphical representations of various computer programs, are displayed on a computer screen.  A user performs a task, such as executing a computer program, by selecting the icon that corresponds to the computer program with an input device, like a computer mouse.  After selecting the icon with the mouse, a specific area in which the program appears on the screen, called a window, is displayed.  The user then uses the program by typing in or using the mouse within the window.  If the user wishes to execute another computer program, another icon is selected, which in turn opens another window on the screen.  Often a computer screen may have numerous windows open and overlapping each other, thereby making the screen appear cluttered and disorganized. 
While the graphics-based operating systems and operations represent an improvement over the text-based operating systems, a user is still required to use a mouse or a keyboard to perform what would be a natural task in the real word.  For example, many graphics-based operating systems are designed to simulate a desk top.  On a real desk top, if a user wanted to work on a new project, he or she would simply pick up the document and move it into the work area of their desk.  With current graphics-based operating systems, for a user to do the same thing on a computer, a user would have to use a mouse or keyboard to select an icon, open a new window, and adjust the size of the new window to occupy the desired area on the computer screen.  Therefore, the user is required by the operating system to perform extra steps using a mouse that are not normally done by hand in the real world. 
In the next generation of personal computers, it is desirable to remove barriers that exist between the user and the computer system itself.  It is desirable that the user not be required to input commands using a keyboard or computer mouse so that the user becomes more interactive with the computer system.  Also, it is desirable that an operating system be provided that allows the user to perform a task in a way that is intuitive to the user and in a way that is more analogous to the way in which the task is done in the real world.  Finally, it is desirable to have an operating system where the user can easily eliminate extra windows that appear on a computer so that the screen does not become cluttered.