IEEE Bushy Tree

IBM had started work on OS/2 version 2.0 probably around 1988, while Microsoft and IBM were working on OS/2 1.2. This coincided with Gordon Letwin's book, Inside OS/2 which had outlined the features for OS/2 written for 386 computers. The chief architect for OS/2 2.0 was Michael S. Kogan, who also co-wrote the book The Design of OS/2.

A beta version was released sometime in November 1991. Features were missing and unfinished, including seamless Windows 3.0 to OS/2 compatibility. It was able to run Windows application, but only as full screen sessions. The full release of OS/2 2.0 was very different from previous versions. The biggest difference being the Workplace Shell GUI. The new interface was object oriented treating all objects (such as drives, printers, program and so on) as objected. The objects could be manipulated (moved, copied, printed and so on). The Workplace Shell also made use of the the second mouse button.

OS/2 2.0 has been regarded as the first widely used 32-bit operating systems for PCs. It offered programmers a full programming model instead of 64k segmented programming. Due to time constraints and compatibility issues, OS/2 2.0 still had 16-bit parts to it. For example, the Graphics Engine wasn't made into a 32-bit version until OS/2 version 2.1. Device drivers and large parts of the kernel were 16-bit required in order to support older devices and applications. Major parts of the system, such as the Multiple Virtual DOS Machine, the memory manager were completely new an fully 32-bit. Also of note, version 2.0 was written in C, unlike previous versions which were written in assembly.

OS/2 version 2.0 was able to run in Virtual 8086 mode from the Intel 386 and later CPUs. It was also able to run windowed and fullscreen applications, all at the same time, and allow the users to create platform-specific sessions. Different versions of DOS (such as 4.0, 5.0, and even CP/M) were allowed to boot. Running Windows applications seamlessly from OS/2 2.0 was still a challenge as much as it was in earlier versions on OS/2. Running DOS applications, however, proved to be OS/2's real strength given it's excellent DOS support.

As with OS/2 1.x, OS/2 2.0 suffered from lack of applications. The newer 32-bit applications took a while to appear on the market, aside from the very few that were offered at the time (mostly from IBM). After the rift between Microsoft and IBM, IBM developed their own C compiler in order to program applications for the OS/2. The compiler was known as CSet/2, which was sold in one of it's three packages: C/C++ Tools, WorkFrame/2 and OS/2 Toolkit. This, along with IBM's debugger, IPMD proved to be powerful tools in OS/2 application development. Over time, other companies have introduced (some even more powerful) software development programming tools.

In short, OS/2 2.0 certainly showcased what a 386-based PC could do, even if it didn't take a lion's share of the market.[1]

In May 1993, IBM released OS/2 version 2.1. Visually, it didn't look any different than 2.0. One major difference was the inclusion of the Multimedia Presentation Manager/2. As was previously mentioned, a 32-bit Graphics Engine was also included, along with APM support (which was geared towards laptop computers). And, at long last, OS/2 2.1 offered a wider selection of printers and display drivers than with prior versions.

OS/2 for Windows done away with Win-OS/2, and would use the existing Windows 3.1 installation, although it wasn't actually required.

Applications for OS/2 2.1 grew rapidly as IBM successfully managed to convince many big developers to develop OS/2 versions of their products. These companies included Borland, Novell, Lotus and WordPerfect. The available compilers for OS/2 2.0 were about the same as they were for OS/2 2.0 with the exception of Watcom C/C++ version 10.

OS/2 2.11 SMP was released in July 1994 and it was marketed as one of the first symmetric multiprocessing enabled PC OSes. Because of the high cost and scare market of SMP hardware, coupled with the then dominance of the single processor PC, the SMP wasn't in high demand. OS/2 2.11 SMP was able to run different processes on different CPUs and threads within a single process as well. Even applications not designed for SMP can take advantage of the multithreading.

Visibly, versions 2.1 and 2.11 weren't all that interesting. Technically, they were substantially better and attracted users who were frustrated with Windows 3.1's shortcomings, but didn't want to go back to using DOS.[2]

OS/2 Warp 4.0 Branch
Preceded by
IBM OS/2 1.x
IBM OS/2 2.x Followed by
IBM OS/2 Warp 3.0
Windows XP Branch
Influenced by
IBM OS/2 2.x Influenced