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

Initially, PM was based on Windows GUI code, and often had developments performed in advance, like the support for proportional fonts ( which appeared in Windows only in 1990 ).

One of the divergences regarded the position of coordinate ( 0, 0 ), which was at the left top in Windows, but at left-bottom ( as in Cartesian coordinates ) in PM.

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.

Both companies were hoping that at some point users would migrate to OS / 2.

A somewhat similar situation occurred in the 1990s with customers sticking to " old " Windows, although MS would have preferred them to switch to NT.