Components of the Microsoft Windows NT or Windows 2000 operating system that support the running of applications from different operating system architectures. Environmental subsystems provide the necessary “environment” in which these applications can run. They are an essential part of the Windows NT operating system that enables cross-platform support for applications written for different operating systems.
Windows NT and Windows 2000 include the following environmental subsystems:
MS-DOS-based applications run on Windows NT in the context of a Win32 application called a Virtual DOS Machine (VDM) that emulates an MS-DOS environment.