Environmental subsystems are central components of

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also i ...

s of the

Windows NT Windows NT is a proprietary graphical operating system produced by Microsoft, the first version of which was released on July 27, 1993. It is a processor-independent, multiprocessing and multi-user operating system. The first version of Win ...

type. They allow the operating system to run software developed for the platform in question. For example, Windows NT 4.0 has four environmental subsystems, viz Win32, DOS or Win16,

OS/2 OS/2 (Operating System/2) is a series of computer operating systems, initially created by Microsoft and IBM under the leadership of IBM software designer Ed Iacobucci. As a result of a feud between the two companies over how to position OS/2 r ...

, and

POSIX The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines both the system- and user-level application programming inter ...

, the latter of which is a Unix standard. The latter resides primarily in the Dynamic Link Library ''posix.dll''. The environmental subsystems are one part of the strategy Microsoft developed for making the Windows NT stream of operating systems a hub for multi-platform computing Others include four

Hardware Abstraction Hardware abstractions are sets of routines in software that provide programs with access to hardware resources through programming interfaces. The programming interface allows all devices in a particular class ''C'' of hardware devices to be acce ...

layers, one for Intel processors, three for RISC processors (DEC Alpha, PowerPC, Mips), and a driver for the HPFS, the standard for OS/2. Since Windows 2000, the

FAT32 File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by ...

file system first introduced with Windows 95 has also been present, with HPFS deprecated then being omitted in later systems. A third-party driver for FAT32 can be used on the earlier NT operating systems. Therefore, Windows NT as of version 4.0 had a default of four file systems (

NTFS New Technology File System (NTFS) is a proprietary journaling file system developed by Microsoft. Starting with Windows NT 3.1, it is the default file system of the Windows NT family. It superseded File Allocation Table (FAT) as the preferred fil ...

, HPFS,

FAT12 File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by ...

, and

FAT16 File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by ...

), and installations of the system with a driver allowing access to a fifth FAT32) are very common, and tools allowing access to Unix file systems are also in existence. Interoperability with Novell Netware is generally implemented at the applications and systems programming level rather than at the kernel and data link layer and therefore further from the physical hardware.

References

Windows NT architecture {{computing-stub