OS/2

OS/2 (Operating System/2) is an operating system originally developed jointly by IBM and Microsoft as an advanced successor to DOS which added support for protected mode and preemptive multitasking. The first version was released in 1987, although it only supported a command line interface. OS/2 1.1, released a year after in 1988 notably introduced the Presentation Manager, a graphical user interface partially developed in tandem with the contemporary Windows 2.x. However, despite the similarities, there were some key differences between Windows and the Presentation Manager that made it practically impossible to write an application for one platform and then recompile the source code for the other without large changes.

After Microsoft broke up with IBM following the success of Windows 3.0, the latter continued development of OS/2 on its own. OS/2 2.0, released in 1992, introduced support for 32-bit applications, removed almost all Microsoft-written code and introduced a new shell called the Workplace Manager. The new version also included improvements to DOS compatibility, as users were now able to run multiple DOS applications at once via the MVDM (Multiple Virtual DOS Machines). This in turn was used to build Win-OS/2, a subsystem which ran a modified version of Windows 3.0 (later updated to Windows 3.1) on top of MVDM and provided integration between Windows and OS/2 apps. IBM leveraged this in their marketing campaign, which promoted OS/2 as "a better DOS than DOS, a better Windows than Windows".