Microsoft POSIX subsystem
Microsoft POSIX subsystem is one of four subsystems shipped with the first versions of Windows NT, the other three being the Win32 subsystem which provided the primary API for Windows NT, plus the OS/2 and security subsystems.
Features
The subsystem only implements the POSIX.1 standard – also known as IEEE Std 1003.1-1990 or ISO/IEC 9945-1:1990 – primarily covering the kernel and C library programming interfaces which allowed a program written for other POSIX.1-compliant operating systems to be compiled and run under Windows NT. The Windows NT POSIX subsystem did not provide the interactive user environment parts of POSIX, originally standardized as POSIX.2. That is, Windows NT did not provide a POSIX shell nor any Unix commands out of the box, except for pax. The NT POSIX subsystem also did not provide any of the POSIX extensions that postdated the creation of Windows NT 3.1, such as those for POSIX Threads or POSIX IPC.Background
The NT POSIX subsystem was included with the first versions of Windows NT because of 1980s Federal [government of the United States|US federal government] requirements listed in Federal Information Processing Standard 151-2. This standard required that certain types of government purchases be POSIX-compliant, so that if Windows NT had not included this subsystem, computing systems based on it would not have been eligible for some government contracts. Windows NT versions 3.5, 3.51 and 4.0 were certified as compliant with FIPS 151-2.The runtime environment of the subsystem is provided by two files: and. A POSIX application uses to communicate with the subsystem while communicating with to provide display capabilities on the Windows desktop.