POSIX was included into Windows NT to allow programs written to the POSIX specification to run under WinNT. POSIX is not designed to run programs made for another OS on NT. POSIX is not OS specific. NT incorporated the POSIX.1 standard, which is also known as the POSIX ISO standard, which defines a system's API for C language programming.

POSIX requires case-sensitive naming, hard links and POSIX.1 library compliances.

Under Windows NT, the following files deal with POSIX:

    This is loaded with the first POSIX program executed and remains resident until removed from memory.

    This file handles communications between the POSIX subsystem and the Executive Services of Windows NT.

    This file is the dynamic link library that contains the routines that POSIX specifies must be present within an operating system.

    Blowdart notes that Win2K supports the POSIX subsystem.