Presentation Manager

Presentation Manager (PM) is the graphical user interface (GUI) that IBM and Microsoft introduced in version 1.1 of their operating system OS/2 in late 1988.

The OS/2 programming model was thought to be cleaner, since there was no need to explicitly export the window procedure, no WinMain, and no non-standard function prologs and epilogs.

One of the most-cited reasons for the IBM-Microsoft split was the divergence of the APIs between Presentation Manager and Windows, which was probably driven by IBM.

In practice it became impossible to recompile a GUI program to run on the other system; an automated source code conversion tool was promised at some point.

There is a significant integration of the GUI layer with the rest of the system, but it is still possible to run certain parts of OS/2 from a text-console or X window, and it is possible to boot OS/2 into a command-line environment without Presentation Manager (e.g. using TSHELL[4] ).

Both CXI and PM/X were submitted to the Open Software Foundation for consideration as OSF's new user interface standard for Unix, which eventually became Motif.

An important problem was that of the single input queue: a non-responsive application could block the processing of user-interface messages, thus freezing the graphical interface.