However, 16-bit Windows programs will not work at all when we move to 64-bit Windows (and 32-bit programs are run using WOW), so it’s time to start replacing them. Windows XP is a 32-bit operating system and runs 16-bit programs via a bit of a bodge known as Windows NT Virtual DOS Machine support (NTVDM).
It is used to provide an Environment for 16 bit process to execute on a 32 bit platform. It is also known as Windows NT Dos Virtual Machine which belongs to Microsoft Windows Operating Systems.
Enable Access to 16-bit Applications from Registry or Group Policy.