calls for DOS functions into Windows NT memory calls. is the emulation layer that emulates 16-bit Windows. Windows 2000 and Windows XP added Sound Blaster 2.0 emulation. 16-bit virtual device drivers and DOS block device drivers (e.g., RAM disks) are not supported. Inter-process communication with other subsystems can take place through OLE, DDE and named pipes. Since virtual 8086 mode is not available on non-x86-based processors (more specifically, MIPS, DEC Alpha, and PowerPC) NTVDM was instead implemented as a full emulator in these versions of NT, using code licensed from Insignia's SoftPC. Up to Windows NT 3.51, only 80286 emulation was available. With Windows NT 4.0, 486 emulation was added. NTVDM is not included with 64-bit versions of Windows prior to Windows 11 or ARM32 based versions such as Windows RT or Windows 10 IoT Core. Windows 10 is the final version of Windows to include this component. This component has since been discontinued, as Windows 11 dropped support for 32-bit processors. Commands The following list of commands is part of the Windows XP MS-DOS subsystem. APPEND DEBUG EDIT EDLIN EXE2BIN FASTOPEN FORCEDOS GRAPHICS LOADFIX LOADHIGH (LH) MEM NLSFUNC SETVER SHARE Security issue In January 2010, Google security researcher Tavis Ormandy revealed a serious security flaw in Windows NT's VDM implementation that allowed unprivileged users to escalate their privileges to SYSTEM level, noted as applicable to the security of all x86 versions of the Windows NT kernel since 1993. This included all 32-bit versions of Windows NT, 2000, XP, Server 2003, Vista, Server 2008, and Windows 7. Ormandy published a proof-of-concept exploit for the vulnerability. Prior to Microsoft's release of a security patch, the workaround for this issue was to turn off 16-bit application support, which prevented older programs (those written for DOS and Windows 3.1) from running. 64-bit versions of Windows are not affected since the NTVDM subsystem is not included. Once the Microsoft security patches had been applied to the affected operating systems the VDM could be safely reenabled. Limitations A limitation exists in the Windows XP 16-bit subsystem (but not in earlier versions of Windows NT) because of the raised per-session limit for GDI objects which causes GDI handles to be shifted to the right by two bits, when converting them from 32 to 16 bits. As a result, the actual handle cannot be larger than 14 bits and consequently 16-bit applications that happen to be served