Each application is responsible for drawing or refreshing its own windows and menus, in response to these messages. The OS/2 environment subsystem supports 16-bit character-based OS/2 applications and emulates OS/2 1.x, but not 32-bit or graphical OS/2 applications as used with OS/2 2.x or later, on x86 machines only.[3] To run graphical OS/2 1.x programs, the Windows NT Add-On Subsystem for Presentation Manager must be installed.[3] The last version of Windows NT to have an OS/2 subsystem was Windows 2000; it was removed as of Windows XP.[4][5] The POSIX environment subsystem supports applications that are strictly written to either the POSIX.1 standard or the related ISO/IEC standards. This subsystem has been replaced by Interix, which is a part of Windows Services for UNIX.[4] This was in turn replaced by the Windows Subsystem for Linux.