This chapter introduces the purpose of Microsoft Windows version 3.1 virtual devices. You create a Windows virtual device for your hardware device, MS-DOS̉ device driver, or terminate-and-stay resident (TSR) program if it is not 100 percent compatible with the devices or software supported by Windows version 3.1 virtual devices. You also create a Windows virtual device if you want to offer Windows users access to unique features of your device or software.