One of the principal design goals of Windows is to provide visual access to most, if not all, applications at the same time. In a multitasking environment, it is important to give all applications some portion of the screen; this ensures that the user can interact with all applications. Some systems do this by giving one program full use of the screen while other programs wait in the background. In Windows, every application has access to some part of the screen at all times.
Summary: Windows lets multiple applications share the screen.
An application shares the display with other applications by using a “window” for interaction with the user. Technically, a window is little more than a rectangular portion of the system display that the system grants use of to an application. In reality, a window is a combination of useful visual devices, such as menus, controls, and scroll bars, that the user uses to direct the actions of the application.
In the standard DOS environment, the system automatically prepares the system display for your application. Typically, it does so by passing a file handle to the application. You can then use that file handle to send output to the system display using conventional C run-time routines or DOS system calls. In Windows, you must create your own window before performing any output or receiving any input. Once you create a window, Windows provides a great deal of information about what the user is doing with the window. Windows automatically performs many of the tasks the user requests, such as moving and sizing the window.
Another advantage to developing in the Windows environment is that, in contrast to a standard C program, which has access to a single screen “surface,” a Windows application can create and use any number of overlapping windows to display information in any number of ways. Windows manages the screen for you, controls the placement and display of windows, and ensures that no two applications attempt to access the same part of the system display at the same time.