OS/2 Version 2.0 provides the capability for Microsoft Windows applications to run under OS/2 Version 2.0, in virtual DOS machines. This support allows applications written for Windows 3.0 and previous versions of Windows to coexist and execute concurrently in the same machine.
Each Windows applications executes as a protected mode process. Windows applications are therefore subject to the full memory protection facilities provided to protected mode applications under OS/2 Version 2.0, and are protected from one another and from DOS or OS/2 applications executing in the system. This is in contrast to the native Windows 3.0 environment, where limited protection is provided for Windows 3.0 applications, and none at all for DOS applications unless Windows is running in enhanced mode.
The execution of Windows applications as protected mode tasks also allows these applications to take full advantage of the pre-emptive multitasking capabilities of OS/2 Version 2.0, with full pre-emptive multitasking between Windows applications, DOS applications and OS/2 applications. This is again in contrast to the native Windows 3.0 environment, where pre-emptive multitasking is available only for DOS applications, only when Windows 3.0 is running in enhanced mode, and only when no input/output operations are being performed, thereby impacting performance and preventing many applications written for previous versions of Windows from executing. OS/2 Version 2.0 has no such restriction.
As with DOS applications, Windows applications may make use of EMS and XMS memory extenders in order to access memory above 640 KB. This support is provided in an identical manner to that provided for DOS applications.
Support for Microsoft Windows applications under OS/2 Version 2.0 is discussed in more detail in OS/2 Version 2.0 - Volume 2: DOS and Windows Environment.