The 80386 processor and VDM component of OS/2 Version 2.0 together emulate a 8086 processor, keyboard, display, BIOS and other supporting hardware; in effect, a complete "virtual Personal Computer". It is therefore possible for "real" DOS to be loaded in a VDM session. Control is passed to the boot record (the first sector) of the DOS system diskette, which in turn loads and initializes the rest of the DOS kernel, just as it does when booting on a physical PC.
Indeed, the VDM environment is so similar to a real PC environment that VMB can actually support any 8086 operating system kernel, such as Digital Research's DR-DOS** and CP/M**, Microsoft MS-DOS**, or even a PS/2 reference diskette (but do not attempt to run diagnostics or change the configuration from a VDM; the results are unpredictable). However, since the purpose of VMB is to run current DOS applications, formal IBM support is announced for IBM PC DOS 3.x, 4.0, and 5.0 only.
Table "Free Base Memory" shows the amount of available base memory for MVDM DOS Emulation, DOS in a VMB session, and native DOS. These figures show the amount of memory available after loading the operating system and mouse, EMS and XMS support.
A VDM using VMB is similar in function to any other virtual DOS machine. Multiple VDMs may be started and operated concurrently using Virtual Machine Boot. Each runs in its own virtual 8086 machine; access to hardware and other system resources is managed by MVDM and the underlying OS/2 Version 2.0 operating system.