An operating system for PCs developed originally by Microsoft Corporation and IBM, but sold and managed solely by IBM. OS/2 is compatible with DOS and Windows, which means that it can run all DOS and Windows programs. However, programs written specifically to run under OS/2 will not run under DOS or Windows.

Since its introduction in the late 80s, OS/2 has traveled a particularly rocky road. The first releases were hampered by a number of technical and marketing problems. Then Microsoft abandoned the project in favor of its own operating system solution, Microsoft Windows. That break spawned a feud between the two computer giants that is still being played out in many arenas.