Operating System/2 (OS/2 Warp) was originally developed as a joint project between IBM and Microsoft. It's intention was to replace the antiquated Disk Operating System (DOS) as the operating system of choice. At the time, DOS was at version 3.x, and IBM and Microsoft both realized that with the advent of the Intel 80286 in the mid-1980's, it was quickly becoming obsolete. Thus, OS/2 was born, initially as a 16-bit, command-line based operating system. Microsoft worked closely with IBM up to version 1.3. While IBM worked on the "guts," they worked on the new graphical user interface that was due for later versions. OS/2's kernel was developed by IBM from the ground up as the Personal Computer (PC) version of a mainframe operating system, with all of the time-slicing, stability, and other features previously existing solely on those high-end machines.

Around this time (circa 1990), Microsoft's other project, Windows, now at version 3.0, was starting to gain popularity with some users. Previously, Windows had been little more than a task-swapping shell for DOS applications, and was intended to compete with QuarterDeck's DesqView. Users found it appealing becaused it contained some of the GUI elements that were being developed for OS/2. A decision was made to drop all support for OS/2, and go strictly with Windows. However, because of the history they had with IBM, and because they still used so much of their technology (Object Linking and Embedding [OLE] aka ActiveX and Component Object Model [COM] are derived from Dynamic Data Exchange [DDE]), Microsoft to this day maintains a broad-ranging cross-licensing agreement with them. Windows NT was partially based on the OS/2 work that they did for IBM, and Windows 95 also borrows heavily from this code.

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