Interix was an optional, POSIX-conformant Unix subsystem for Windows NT operating systems. Interix was a component of Windows Services for UNIX, and a superset of the Microsoft POSIX subsystem. Like the POSIX subsystem, Interix was an environment subsystem for the NT kernel. It included numerous open source utility software programs and libraries. Interix was originally developed and sold as OpenNT until purchased by Microsoft in 1999. Interix versions 5.2 and 6.0 were respective components of Microsoft Windows Server 2003 R2, Windows Vista Enterprise, Windows Vista Ultimate, and Windows Server 2008 as Subsystem for Unix-based Applications (SUA). Version 6.1 was included in Windows 7 (Enterprise and Ultimate editions) but disabled by default, and in Windows Server 2008 R2 (all editions). It was available as a deprecated separate download for Windows 8 and Windows Server 2012, and is not available at all on Windows 10. Details The complete installation of Interix included (at version 3.5): Over 350 Unix utilities such as vi, ksh, csh, ls, cat, awk, grep, kill, etc. A complete set of manual pages for utilities and APIs GCC 3.3 compiler, includes and libraries A cc/c89-like wrapper for Microsoft Visual Studio command-line C/C++ compiler GNU Debugger X11 client applications and libraries (no X server included, though third party servers were available) Has Unix "root" capabilities (i.e. setuid files) Has pthreads, shared libraries, DSOs, job control, signals, sockets, shared memory The development environment included support for C, C++ and Fortran. Threading was supported using the Pthreads model. Additional languages could be obtained (Python, Ruby, Tcl, etc.). Unix-based software packaging and build tools were available for installing or creating pre-build software packages. Starting with release 5.2 (Server 2003/R2) the following capabilities were added: "Mixed mode" for linking Unix programs with Windows DLLs 64-bit CPU support (in addition to 32-bit) Large file system support on 64-bit systems System V R4 utilities can be optionally installed instead of the default BSD-based utilities MSVC debugging plug-in Database (OCI/ODBC) library connectivity With release 6.0 (Vista and Server 2008) the following new features were added: IPv6 support for socket APIs and daemons Updates to utilities for additional functionality MSVC debugging plug-in enhanced Interix release 6.0 for Vista was only available with the Ultimate and Enterprise editions. Interix release 6.1 was available for Windows Server 2008 R2 and Windows 7 for the Enterprise and Ultimate editions. Support Traditional support was provided by Microsoft for a fee or service