The DOS Emulation kernel which is normally used to support the execution of DOS applications in a VDM is exactly what its name implies; an emulation of the DOS operating system and associated services. While this suffices for most DOS applications, certain applications exist which take advantage of unique and/or undocumented features which exist only in specific versions of DOS.
To allow such applications to be successfully run under OS/2 Version 2.0, the VMB (Virtual Machine Boot) feature is provided. This feature allows a "real" DOS operating system, or indeed most other 8086 operating systems, to be booted in a virtual DOS machine. The operating system may be booted from either a diskette in drive A:, a diskette image on a hard disk, or a partition on a hard disk.
Applications which run using Virtual Machine Boot may take advantage of the EMS, XMS and mouse support provided to virtual DOS machines by OS/2 Version 2.0. This support is provided through stub device drivers supplied with OS/2 Version 2.0; these should be used in preference to the device drivers supplied with the operating system or applications.