In the 1990s, IBM irked Microsoft by selling PCs loaded with its own operating system, OS/2, as an alternative to Windows, and with its SmartSuite productivity software, cutting into the market for Microsoft Office programs. IBM also backed Java, a programming language that doesn't need Windows to run.

Jackson noted that Microsoft retaliated by charging IBM more than other PC makers for copies of Windows.

There were other tactics, too. Months before Windows 95 came out, Microsoft let other PC companies pre-install the operating system on new computers that could go on sale right after the launch. But IBM got its license only 15 minutes before the event.