When Apple (NASDAQ:AAPL) made Mavericks a free OS upgrade, it put tremendous pressure on Microsoft (NASDAQ:MSFT), Fool contributor Tim Beyers says in the following video.

How so? Mr. Softy is now the lone seller of operating system software as a separate product. That won't change soon, either. Microsoft's Windows Division is the company's third-largest unit, having supplied some $18.6 billion in revenue in the last fiscal year.

Much of that comes from selling Windows licenses to PC makers who bundle the software with their machines. Some comes from users and businesses buying upgrade licenses. But now that Apple has followed Google's example and made OS software a free add-on to a machine, Tim says it could get a lot harder for Microsoft to keep that revenue stream flowing.

Should investors sell now and look for better opportunities? Will Apple's Mavericks move help it sell more Macs? Tim answers these questions and more in the video. Please watch now, then leave a comment to let us know what you think.

Fool contributor Tim Beyers owns shares of Apple and Google. The Motley Fool recommends Apple and Google. The Motley Fool owns shares of Apple, Google, and Microsoft. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.