DOS has long been the Achilles heel of the PC and has limited its development. It has also been its strength in that it provides a common platform for all packages. DOS and Windows 3.x operated in a 16-bit mode and had limited memory accessing. Windows 3.0 provided a great leap in PC systems as it provided an excellent graphical user interface to DOS. It suffered from the fact that it still used DOS as the core operating system. Windows 95/98 and Windows NT have finally moved away from DOS and operate as full 32-bit protected-mode operating systems. Their main features are:
• Run both 16-bit and 32-bit application programs.
• Allow access to a large virtual memory (up to 4 GB).
• Support for pre-emptive multitasking ...