/O S too/ IBM and Microsoft's successor to the MS-DOS operating system for Intel 80286 and Intel 80386-based microprocessors. It is proof that they couldn't get it right the second time either. Often called "Half-an-OS". The design was so baroque, and the implementation of 1.x so bad, that 3 years after introduction you could still count the major application programs shipping for it on the fingers of two hands, in unary. Later versions improved somewhat, and informed hackers now rate them superior to Microsoft Windows, which isn't saying much. See second-system effect.
On an Intel 80386 or better, OS/2 can multitask between existing MS-DOS applications. OS/2 is strong on connectivity and the provision of robust virtual machines. It can support Microsoft Windows programs in addition to its own native applications. It also supports the Presentation Manager graphical user interface.
After OS/2 1.x the IBM and Microsoft partnership split. IBM continued to develop OS/2 2.0, while Microsoft developed what was originally intended to be OS/2 3.0 into Windows NT. In October 1994, IBM released version OS/2 3.0 (known as "Warp") but it is only distantly related to Windows NT. This version raised the limit on RAM from 16MB to 1GB (like Windows NT).
IBM introduced networking with "OS/2 Warp Connect", the first multi-user version. OS/2 Warp 4.0 ("Merlin") is a network operating system.