OS/2 (Operating System/2) is a series of computer operating systems, initially created by Microsoft and IBM under the leadership of IBM software designer Ed Iacobucci.[2] As a result of a feud between the two companies over how to position OS/2 relative to Microsoft's new Windows 3.1 operating environment,[3] the two companies severed the relationship in 1992 and OS/2 development fell to IBM exclusively.[4] 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 of OS/2 was initially released in December 1987, and newer versions were released until December 2001.
OS/2 was intended as a protected-mode successor of PC DOS targeting the Intel 80286 processor. 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.[5] Because of this heritage, OS/2 shares similarities with Unix, Xenix, and Windows NT.
Up to $990 million per year was spent developing OS/2 and its replacement. OS/2 sales were largely concentrated in networked computing used by corporate professionals; however, by the early 1990s, it was overtaken by Microsoft Windows NT.
IBM discontinued its support for OS/2 on December 31, 2006.[6] Since then, OS/2 has been developed, supported and sold by two different third-party vendors under license from IBM – first by Serenity Systems as eComStation since 2001,[7] and later by Arca Noae LLC as ArcaOS since 2017.[8][9][10]