Q. Does Windows XP offer any user-mode processes that enable it to run programs developed for other operating systems? Describe two of these subsystems.
Answer: Environmental subsystems are user-mode processes layered in excess of the native executable services to enable Windows XP to run programs developed for other operating systems.
(1) A Win 32 application called the virtual DOS machine (VDM) is offer as a user-mode process to run MS-DOS applications. The VDM can perform or emulate Intel 486 instructions and also provides routines to emulate MS-DOS BIOS services and provides virtual drivers for screen and keyboard and communication ports.
(2) WOW32 (Windows-on-windows) provides kernel as well as stub routines for Windows 3.1 functions. The end routines call the appropriate Win32 subroutines converting the 16-bit addresses into 32-bit addresses.