Multiple DOS applications may be run concurrently under OS/2 Version 2.0, in virtual DOS machines with pre-emptive multitasking and full memory protection. By default, these applications access DOS and hardware services using an emulated version of DOS, which provides these services through the OS/2 operating system. Most of these DOS services are provided outside the 640KB real mode address space in which the DOS application executes, thereby allowing more memory (up to 630KB) for the application and its data.
DOS applications can usually be installed by starting a virtual DOS machine and running the install program from the command prompt. If the installation fails the user can boot the system from a DOS diskette to run the install, provided the hard disk has at least one FAT partition.
A DOS application may be defined as an object on the OS/2 Version 2.0 Workplace Shell desktop or in a folder, and started from the Workplace Shell. Applications defined in this way have their VDM environment configured to support particular application requirements and to allow the application to take full advantage of VDM features. Alternatively, the Migrate Applications facility can be used to place the application in the Workplace Shell and customize the DOS settings
A DOS application may also be started from the DOS or OS/2 command line. However, applications started from the DOS command line inherit the DOS environment settings of the VDM in which the command line is executing, and those started from the OS/2 command line inherit the default settings.
DOS Applications which require access to internal DOS control structures or block device drivers not supported by the DOS Emulation kernel may use the Virtual Machine Boot facility of OS/2 Version 2.0 to load a "real" version of DOS from a diskette or a diskette image stored on fixed disk. This capability allows such applications to run in a VDM.