Microsoft split up its Windows group earlier this year, putting some of the business into the unit that develops the Azure cloud and the rest into the group that works on Office and devices. It's all part of Microsoft's shift to focus on the cloud and artificial intelligence under Ballmer's successor, Satya Nadella.
Still, Windows is producing more and more revenue and a big chunk of profit, even as Nadella changes direction.
"I mean, this less importance on Windows thing I find a humorous thing by the press," Ballmer said in an interview on Monday at the WSJ Tech D.Live event in Laguna Beach, California.
Ballmer said he can't imagine the company would do anything to unwind it.
"If they were, I'd be selling," he said.
Windows revenue increased 5 percent to $19.5 billion in the latest fiscal year, which ended on June 30. That represents more than 17 percent of total revenue. Microsoft doesn't disclose operating income for Windows, but Ballmer said at the conference that the business accounts for $13 or $14 billion of operating profit. If true, that would represent about 40 percent of the total.