Editing Virtual DOS machine (section)

==DOS-based VDMs==
In contrast to these protected mode operating systems, DOS, by default, is a real-mode operating system, switching to protected mode and virtual 86 mode only on behalf of memory managers and DOS extenders in order to provide access to extended memory or map in memory into the first megabyte, which is accessible to normal DOS programs.

DOS-based VDMs appeared with Microsoft's [[Windows/386 2.01]] in September 1987.<ref name="Win386_201"/> DOS-based virtual DOS machines were also present in [[Windows 3.0]], [[Windows 3.1x|3.1x]] and [[Windows for Workgroups|Windows for Workgroups 3.1x]] running in [[386 Enhanced Mode]] as well as in [[Windows 95]], [[Windows 98|98]], [[Windows 98 SE|98 SE]] and [[Windows ME|ME]]. One of the characteristics of these solutions running on top of DOS is that the memory layout shown inside virtual DOS machines are virtual instances of the DOS system and DOS driver configuration run before the multitasker is loaded, and that requests which cannot be handled in protected mode are passed down into the system domain to be executed by the underlying DOS system.

Similar to Windows 3.x 386 Enhanced Mode in architecture, [[EMM386]] 3.xx of [[Novell DOS 7]],<ref name="Schulman_1994_Undocumented-DOS"/><ref name="Paul_1997_NWDOSTIP"/> [[Caldera OpenDOS 7.01]],<ref name="Paul_1997_NWDOSTIP"/><ref name="Caldera_1997_Multi"/> [[DR-DOS 7.02]]<ref name="Caldera_1998_USER"/> (and later) also uses DOS-based VDMs to support pre-emptive multitasking of multiple DOS applications, when the <kbd>EMM386 /MULTI</kbd> option is used.<ref name="Paul_1997_NWDOSTIP"/><ref name="Caldera_1997_Multi"/><ref name="Caldera_1998_USER"/> This component has been under development at [[Digital Research]] / [[Novell]] since 1991<ref group="nb" name="NB_Panther"/> under the codename "Vladivar" (originally a separate device driver <kbd>KRNL386.SYS</kbd><ref name="Schulman_1994_Undocumented-DOS"/><ref name="Paul_1997_NWDOSTIP"/> instead of a module of EMM386). While primarily developed for the next major version of DR&nbsp;DOS, released as Novell DOS 7 in 1994,<ref name="Schulman_1994_Undocumented-DOS"/><ref name="Paul_1997_NWDOSTIP"/> it was also used in the never released [[DR DOS "Panther"]] and "[[Star Trek project|Star Trek]]" project in 1992/1993.