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/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.

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 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.



An earlier family of operating systems for x86 machines from IBM. OS/2 Warp was the client version, and Warp Server was the server version. With add-ons, DOS and Windows applications also ran under OS/2 (see Odin). The server version included advanced features such as the journaling file system (JFS) used in IBM's AIX operating system. Like Windows, OS/2 provided a graphical user interface and a command line interface. See OS/2 Warp, Warp Server and eComStation.

Although highly regarded as a robust operating system, OS/2 never became widely used. However, it has survived in the banking industry, especially in Europe, and many ATM machines in the U.S. have continued to run OS/2 due to its stability.

OS/2 included Adobe Type Manager for rendering Type 1 fonts on screen and providing PostScript output on non-PostScript printers. OS/2's dual boot feature allowed booting into OS/2 or DOS.

The OS/2 Workplace Shell graphical user interface was similar to Windows and the Macintosh. Originally known as Presentation Manager (PM), after Version 2.0, PM referred to the programming interface (API), not the GUI interface itself.

The first versions of OS/2 were single-user operating systems written for 286s and jointly developed by IBM and Microsoft. Starting with Version 2.0, IBM wrote versions for 32-bit 386s and up. Following is the evolution:

OS/2 16-bit Version 1.x
The first versions (1.0, 1.1, etc.) were written for the 16-bit 286. DOS compatibility was limited to about 500K. Version 1.3 (OS/2 Lite) required 2MB RAM instead of 4MB and included Adobe Type Manager. IBM's Extended Edition version included Communications Manager and Database Manager.

OS/2 32-bit Version 2.x - IBM
Introduced in April 1992, this 32-bit version for 386s from IBM multitasked DOS, Windows and OS/2 applications. Data could be shared between applications using the clipboard and between Windows and PM apps using the DDE protocol. Version 2.x provided each application with a 512MB virtual address space that allowed large tasks to be easily managed.

Version 2.1 supported Windows' Enhanced Mode and applications could take full advantage of Windows 3.1. It also provided support for more video standards and CD-ROM drives.

Communications and database management for OS/2 were provided by Communications Manager/2 (CM/2) and Database Manager/2 (DB2/2). CM/2 replaced Communications Manager, which was part of OS/2 2.0's Extended Services option.

OS/2 32-bit Version 3 - IBM
In late 1994, IBM introduced Version 3 of OS/2, renaming it OS/2 Warp. The first version ran in only 4MB of memory and included a variety of applications, including Internet access.

Windows NT - Microsoft
Originally to be named OS/2 Version 3.0, this 32-bit version from Microsoft was renamed "Windows NT" and introduced in 1993. See Windows NT.