What Does Presentation Manager (PM) Mean?
Presentation Manager (PM) is the graphical user interface (GUI) that was jointly developed by Microsoft and IBM and introduced in the OS/2 operating system released in 1988. PM was co-developed by Microsoft and IBM and was a sort of hybrid between Microsoft's Windows and IBM's own mainframe graphical system (GDDM). It was even sometimes called Windows Presentation Manager due to its many similarities in operation with Windows graphical elements and that fact that they were developed in parallel.
Techopedia Explains Presentation Manager (PM)
Presentation Manager, OS/2's GUI, was message-based just like Windows, which allowed for loosely coupled applications, along with other graphical similarities. They even used many identical messages. PM was actually designed to be similar to Windows 2.0 and the application structure was almost identical to the Windows application structure, though compatibility with Windows was not an objective of PM. However, Microsoft used many of the lessons learned in developing Windows to PM development.
PM also had significant differences with Windows, and one of them was the coordinate system having opposite starting points. The 0,0 coordinate in Windows was located in the upper left corner of the screen, but PM's 0,0 was located in the lower left corner. Another difference was that PM had an abstraction layer for calling all drawing operations called Presentation Space (PS), while Windows directed all drawing calls to the Device Context (DC).
Eventually Microsoft and IBM parted ways and IBM acquired and continued to develop Presentation Manager. Microsoft then took what they had made to be Presentation Manager 3.0 and renamed it to Windows NT. OS/2 later became the base for the object-oriented interface called Workplace Shell.