Virtual DOS machine
NTVDM uses NTIO.SYS and NTDOS.SYS, which runs a changed version of COMMAND.COM. The 16-bit system files are smaller versions of their MS-DOS 5.0 counterparts, including IO.SYS, MSDOS.SYS and COMMAND.COM, which remove biases with the FAT file system and can also call the 32-bit NTVDM if needed. NTDOS originally gave a DOS version of 30.00 to programs, but this soon was changed to 5.00 to let more programs to run without being changed However, there are many newer MS-DOS functions and commands added to MS-DOS versions 6.x and in Windows 9x which are not there.