In the Windows NT architecture, environment subsystems (sometimes referred to as personalities) are user space components of the operating system that provide compatibility with an application binary interface. They allow the operating system to run software developed for the platform in question. For example, Windows NT 4.0 has three environment subsystems: Win32 (Windows API), OS/2, and POSIX, the latter of which corresponding a subset of the most common functions in the application programming interfaces of Unix-like systems. The latter resides primarily in the dynamic-link library . The environment subsystems are one part of the strategy Microsoft developed for making the Windows NT family of operating systems a hub for multi-platform computing in addition to other elements of the architecture of Windows NT like the hardware abstraction layer.
See also Architecture of Windows NT Interix Microsoft POSIX subsystem Microsoft Windows library files NTVDM Windows 11#Windows Subsystem for Android Windows Subsystem for Linux WoW64
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