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Tracing the History of the Computer - OS/2


OS/2 is an operating system created by Microsoft and IBM, later developed by IBM exclusively. The name stands for "Operating System/2", because it was introduced as the preferred operating system for IBM's "Personal System/2 (PS/2)" line of second-generation Personal Computers. OS/2 is no longer marketed by IBM, and support for OS/2 will be discontinued December 31, 2006.

OS/2 was intended as a protected mode successor of MS-DOS and Microsoft Windows. Notably, basic system calls were modeled after MS-DOS calls; their names even started with "Dos" and it was possible create "Family Mode" applications: text mode applications that could work on both systems. Because of this heritage, OS/2 is not unlike Windows in many ways, but it also shares similarities with Unix and XENIX.


Enthusiastic beginnings

The development of OS/2 began when IBM and Microsoft signed the Joint Development Agreement in August 1985. However, it took two years for the first product to be delivered.

OS/2 1.0 was announced in April 1987 and released in December as a text mode-only OS. However, it featured a rich API for controlling the video display (VIO) and handling keyboard and mouse events in a sort of protected-mode BIOS. In addition, the video and keyboard APIs were also available to family mode programs running under MS-DOS. A task-switcher named Program Selector was available through the Ctrl-Esc hotkey combination, allowing the user to select among multitasked text-mode applications.

The promised GUI, Presentation Manager, was introduced with OS/2 1.1 in November 1988. With proportional fonts, it was a precursor of the later Windows 3.0 look.

Version 1.2 introduced the HPFS filesystem. HPFS provided a number of improvements over the older FAT filesystem, including long filenames and a form of Alternate Data Streams called Extended Attributes. In addition, extended attributes were also added to the FAT filesystem.

OS/2 and Windows-related books of the late 1980s acknowledged the existence of both systems and promoted OS/2 as the system for the future.


Breakup: the five year itch

The collaboration between IBM and Microsoft unravelled in 1990, between the releases of Windows 3.0 and OS/2 1.3. Initially, at least publicly, Microsoft continued to insist the future belonged to OS/2. However, during this time, Windows 3.0 became a tremendous success, selling millions of copies in its first year. Much of its success was due to the fact that Windows 3.0 (along with MS-DOS) was bundled with most new computers. OS/2, on the other hand, was only available as an expensive stand-alone software package. In addition, OS/2 lacked device drivers for many common devices such as printers, particularly non-IBM hardware. Windows, on the other hand, supported a much larger variety of hardware. The increasing popularity of Windows prompted Microsoft to shift its development focus from cooperating on OS/2 with IBM to building a franchise based on Windows. Several technical and practical reasons contrbuted to this breakup:

  • Differences in API: OS/2 was announced when Windows 1.0 was near completion, and the Windows API already defined. However, IBM requested that this API be significantly changed for OS/2. Therefore, issues surrounding application compatibility appeared immediately. OS/2 designers hoped for source code conversion tools, allowing complete migration of Windows application source code to OS/2 at some point. However, OS/2 1.x did not gain enough momentum to allow vendors to avoid developing for both OS/2 and Windows in parallel. IBM's involvement was much more successful in redefining Windows' visual appearance after the 1.0 release, giving it what is today perceived as the "Windows 3.1 look".
  • OS/2 targeted the 80286 Processor: IBM insisted on supporting the Intel 80286 processor, with its 16-bit segmented memory mode, due to commitments made to customers who had purchased a large number of 80286-based PS/2's because of IBM's promises surrounding OS/2. Until release 2.0 in April 1992, OS/2 ran in 16-bit protected mode and therefore could not benefit from the Intel 80386's much simpler 32-bit flat memory mode and virtual 8086 mode features. This was especially painful in providing support for DOS applications. While, in 1988, Windows/386 2.1 could run several preemptively-multitasked DOS applications, including EMS memory emulation, OS/2 1.3, released in 1991, was still limited to one 640KB "DOS box".

Given these issues, Microsoft felt it was necessary to work in parallel on a version of Windows which was more future-oriented and more portable. The hiring of Dave Cutler, former VMS architect, in 1988 created an immediate competition with the OS/2 team, as Dave did not think much of the OS/2 technology and wanted to construct a "VMS plus" rather than just a "DOS plus". His "NT OS/2" (which supposedly stood for New Technology), was a completely new architecture.

IBM grew concerned about the delays in development of OS/2 2.0 and the diversion of IBM funds earmarked for OS/2 development towards Windows. Initially, the companies agreed that IBM would take over maintenance of OS/2 1.0 and development of OS/2 2.0, while Microsoft would continue development of OS/2 3.0. In the end, Microsoft decided to recast NT OS/2 3.0 as Windows NT, leaving all future OS/2 development to IBM. From a business perspective, it was logical to concentrate on a consumer line of operating systems based on DOS and Windows, and to prepare a new high-end system in such a way as to keep good compatibility with existing Windows applications. While waiting for this new high-end system to develop, Microsoft would still receive licensing money from XENIX and OS/2 sales. Windows NT's OS/2 heritage can be seen in its initial support for the HPFS filesystem, text mode OS/2 1.x applications, and OS/2 LAN Manager network support.

32-bit era

OS/2 2.0, released in April 1992, was touted by IBM as "a better DOS than DOS and a better Windows than Windows". For the first time, OS/2 was able to run more than one DOS application at a time. This was so effective that it allowed OS/2 to actually run a slightly-modified copy of Windows 3.0, itself a DOS application, including Windows 3.0 applications. Also new in version 2.0 was the Workplace Shell, an object-oriented environment that ran on top of the older Presentation Manager GUI.

DOS compatibility

Because of the limitations of the Intel 80286 processor, OS/2 1.x could only run one DOS program at a time, and did this in a way that allowed the DOS program to have total control over the computer. A problem in DOS mode could crash the entire computer. In contrast, OS/2 2.0 could benefit from the virtual 8086 mode of the Intel 80386 processor in order to create a much safer virtual machine in which to run DOS programs. This included an extensive set of configuration options to optimize the performance and capabilities given to each DOS program. Like nearly all 32-bit operating environments, including Windows, OS/2 could not run protected-mode DOS programs using the older VCPI interface; it only supported programs written according to DPMI.

Windows 3.x compatibility

Compatibility with Windows 3.0 (and later Windows 3.1) was achieved by adapting Windows code to run inside a virtual 8086 process. Originally, a nearly complete version of Windows code was included with OS/2 itself: Windows 3.0 in OS/2 2.0, and Windows 3.1 in OS/2 2.1; however, IBM later developed versions of OS/2 that would use whatever Windows version the user had installed previously, patching it on the fly, and sparing the cost of an additional Windows license. It could either run full-screen, using its own set of video drivers, or "seamlessly", where Windows programs would appear directly on the OS/2 desktop. The process containing Windows was given fairly extensive access to hardware, especially video, and the result was that switching between a full-screen WinOS/2 session and the Workplace Shell could occasionally cause issues.

Multiple Windows applications ran in a single Windows process, just as they would under Windows on DOS. However, to achieve true isolation between Windows 3.x programs, OS/2 could run multiple copies of Windows in parallel. This approach required considerable system resources, especially memory. In addition, it was possible to use DDE between OS/2 and Windows applications, and OLE between Windows applictations only.

Native features

OS/2 2.0 provided a 32-bit API for native programs, though the OS itself was a mixture of 16-bit and 32-bit code. It also included a new GUI environment called the Workplace Shell. This was a fully object-oriented GUI that was a signficant departure from the previous GUI. Rather than merely providing an environment for program windows (such as the Program Manager), the Workplace Shell provided an environment in which a user could manage programs, files and devices by manipulating objects on the screen.

A significant factor in the spread and acceptance of OS/2 2.0 and later releases was Team OS/2, a grass-roots advocacy group formed in 1992.

The "Warp" years

OS/2 version 3.0, released in 1994, was labelled as "OS/2 Warp" to highlight the new performance benefits, and generally to freshen the product image. "Warp" had originally been the internal IBM name for the release: IBM had used Star Trek terms as internal names for past OS/2 releases, and this one seemed appropriate for external use as well. At the launch of OS/2 Warp in 1994, Patrick Stewart was to be the Master of Ceremonies; however Kate Mulgrew of the then-upcoming series Star Trek: Voyager was substituted at the last minute.

OS/2 Warp offered a host of benefits over OS/2 2.1, notably broader hardware support, greater multimedia capabilities, Internet-compatible networking, and it included a basic office application suite. OS/2 Warp Connect followed, which had full network support built-in.

In 1996, Warp 4 added Java and voice recognition software. IBM also released server editions of Warp 3 and Warp 4 which bundled IBM's LAN Server product directly into the operating system installation. Warp 4 was the last widely-distributed version of OS/2, and IBM soon announced the end of marketing the operating system to individual users.

Fading out

Overall, OS/2 failed to catch on in the mass market and is today little used outside certain niches where IBM traditionally had a stronghold. For example, many banks, especially Automated Teller Machines, run OS/2 with a customized user interface; French SNCF national railways used OS/2 1.x in thousands of ticket selling machines. Nevertheless, OS/2 still maintains a small and dedicated community of followers.

Although IBM began indicating shortly after the release of Warp 4 that OS/2 would eventually be withdrawn, the company has only recently published a definite end-of-support date (2006-12-31). Sales of OS/2 stopped on 2005-12-23. The latest IBM version is 4.52, which was released for both desktop and server systems in December 2001. A company called Serenity Systems has been reselling OS/2 since 2001, calling it eComStation.


The graphic system has a layer named Presentation Manager that manages windows, fonts, and icons. This is similar in functionality to a non-networked version of X11 or the Windows GDI. On top of this lies the Workplace Shell (WPS) introduced in OS/2 2.0. WPS is an object-oriented shell allowing the user to perform traditional computing tasks such as accessing files, printers, launching legacy programs, and advanced object oriented tasks using built-in and 3rd party application objects that extended the shell in an integrated fashion not available on any other mainstream operating system. WPS follows IBM's Common User Access user interface standards.

WPS represents objects such as disks, folders, files, program objects, and printers using the System Object Model (SOM), which allows code to be shared among applications, possibly written in different programming languages. A distributed version called DSOM allowed objects on different computers to communicate. DSOM is based on CORBA. SOM is similar to, and a direct competitor to, Microsoft's Component Object Model. SOM and DSOM are no longer being developed.

OS/2 also includes a radical advancement in application development with compound document technology called OpenDoc, which was developed with Apple. OpenDoc proved interesting as a technology, but was not widely used or accepted by users or developers. OpenDoc is also no longer being developed.

The multimedia capabilities of OS/2 are accessible through Media Control Interface commands. The last update (bundled with the IBM version of Netscape Navigator plugins) added support for MPEG files. Support for newer formats like PNG, progressive JPEG, DivX, OGG, MP3 comes from third parties. Sometimes it is integrated with the multimedia system, but in other offers it comes as standalone applications.



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