Most people are not aware that after the failure of the PS/2 attempt to control the PC market, IBM tried a third time using 7 patents it had for the PC AT (they didn't have any on the original PC or the XT). In the first half of the 1990s they went after the chipset makers (mostly in Japan at that time) and in the second half of the 1990s they went after the PC makers themselves all around the world. The would threaten to sue for all machines made up to that point unless they licensed not only the 7 AT patents (which would expire in 2001) but also a bunch of other unrelated patents that were much newer. As far as I know everybody signed the deal, which meant that IBM could make money without actually making any PCs themselves.