Normally written "OS/2".
/O S too/ IBM and Microsoft's anointed successor to 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. The 2.x versions are said to have improved somewhat, and informed hackers now rate them superior to Microsoft Windows, which isn't saying much. See second-system effect.
OS/2 is a single-user multitasking operating system that works with up to 16 megabytes of memory and can run existing MS-DOS applications one at a time. The 386-specific version of OS/2 will trigger a special 386 "virtual mode" allowing it to run multiple MS-DOS applications at the same time.
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.
OS/2 supports hybrid multiprocessing (HMP), which provides some elements of symmetric multiprocessing (SMP), using add-on IBM software called MP/2. OS/2 SMP was planned for release in late 1993.
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 3.0 of OS/2 (also known as "Warp") but it is only distantly related to Windows NT.
(20 Jul 1995)