At Apple's event to unveil its new iPads Tuesday, software lead Craig Federighi also said the next version of its Mac operating system, OS X Mavericks, will be free.

The new "pricing" model will be much like the iPhone, which gets free software updates. But this is the first time Apple's classic, flagship operating system has been free. For consumers, that means Windows is the last mainstream operating system with a price tag.

It also brings more into focus the difference between Microsoft and Apple. While making the announcement, Federighi specifically called out Windows for its $200 price tag for Windows 8. (There are a variety of prices, but still, the principle applies.) Instead of selling its operating system, Apple is giving it away as a way to help sell its hardware.

Meanwhile, Microsoft is trying to reorient itself into being a devices and services company that looks a lot like Apple, while still selling its Windows operating system. Windows still has the widest distribution on PCs, but that market is gradually being eaten up by smartphones and tablets — where the software, whether it's Android or iOS, comes free with the hardware.

Microsoft is the last company standing still selling its operating system that's constantly tried to find an answer to Apple, whether that's updating its operating system to work better on a tablet or building its own tablet. It's also been doing a lot of soul searching, completing a major reorganization and searching for a new CEO as it tries to decide what its future is — whether it's wrapping around Windows or selling its services online.

Obviously, companies can still buy enterprise software, such as server operating systems. But as a consumer, there is no mainstream operating system other than Windows that actually has a price tag. Android is free, Ubuntu is free, iOS is free, and now Mac OS X is free.

New devices like the Surface come with Windows 8 — and that might be the last version that Microsoft can charge for an update.