Windows Evolution over Timeline
Windows evolution started from 1981 as initially, Windows was a graphical shell that ran on top of DOS. This functionality continued through the Windows 95 line of OSs until it come to an end with Windows Millennium Edition (ME).
Starting in 1993, Microsoft sold an another OS named Windows NT that depended on an entirely different architecture. It used the same graphical interface, but it did not run on top of DOS. Windows NT 4.0 inherited the modern Desktop and Start menu concept from Windows 95, and this basic interface concept is still used in Windows 7 today. DOS no longer exists in Windows 7, but the Command Prompt interface provides a command line or text mode interface for interacting with the OS. The Command Prompt is very similar to DOS, and it is clearly based on its predecessor.
Above Figure shows a timeline that compares the evolution of PC hardware with the evolution of the Windows OS. As the image portrays, more powerful hardware has allowed for more types in the OS, so that we can use the graphically rich interfaces with animations and special effects that we use today. The memory amounts listed in figure do not represent the maximum supported memory of the named systems, but rather the common memory amounts used with them.