OS/2

OS/2 is a series of computer operating systems, initially created by Microsoft and IBM, then later developed by IBM exclusively. The name stands for "Operating System/2," because it was introduced as part of the same generation change release as IBM's "Personal System/2 (PS/2)" line of second-generation personal computers. The first version was released in December 1987 and newer versions were released until December 2001.

OS/2 was intended as a protected mode successor of PC-DOS. Notably, basic system calls were modeled after MS-DOS calls; their names even started with "Dos" and it was possible to create "Family Mode" applications: text mode applications that could work on both systems. Because of this heritage, OS/2 shares similarities with Unix, Xenix, and Windows NT in many ways.

OS/2 is no longer marketed by IBM, and IBM standard support for OS/2 was discontinued on 31 December 2006.